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Synthesis behavior and magnetic properties of Mg-Ni co-doped Y-type hexaferrite prepared by sol-gel auto-combustion method
Materials Chemistry and Physics xxx (2016) 1e11
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Synthesis behavior and magnetic properties of Mg-Ni co-doped Y-type hexaferrite prepared by sol-gel auto-combustion method Y. Alizad Farzin a, *, O. Mirzaee b, A. Ghasemi c a
School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 14395-553, Tehran, Iran Department of Materials Science and Engineering, University of Semnan, Iran c Department of Materials Engineering, Malek Ashtar University of Technology, Iran b
h i g h l i g h t s Nano crystalline Y-type hexaferrites has been synthesized via sol-gel auto combustion method. Effect of Ni and Mg ions on synthesis behavior and magnetic properties of Co2Y hexaferrite was investigated. Thermal behavior of Mg ions caused reduction in synthesis temperature to 950 C. Average thickness of particles has been decreased by the increase of Mg and Ni ions. The coercivity strongly decreased with increasing of calcination temperature.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 October 2014 Received in revised form 13 April 2016 Accepted 25 April 2016 Available online xxx
Nano crystalline Y-type hexaferrites with chemical composition of Sr2Co2xMgx/2Nix/2Fe12O22 (x of 0 e0.6) were prepared by sol-gel auto-combustion technique at the temperature ranging from 900 to 1150 C. The prepared samples were characterized by differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), and vibrating sample magnetometer (VSM). The results demonstrated that single phase co-doped Y-type hexaferrites with space group of R3/m were prepared at 1000 C and crystallite size of the samples was calculated in the range of 45e63 nm. Also, below this temperature, some intermediate phases such as hematite, spinel ferrite, and SrO were observed. All of the synthesized hexaferrites showed homogeneous distribution and hexagonal plateletlike shapes which were suitable for microwave absorption. Hysteresis loop measurements revealed that the presence of hematite as a second phase caused a reduction in the saturation magnetization. Moreover, it was observed that, with increasing the calcination temperature to above 1000 C, saturation magnetization demonstrated no significant changes while coercivity reduced from 950 to 250 Oe, which was due to transition from single to multi domain structures. © 2016 Elsevier B.V. All rights reserved.
Keywords: Nanostructures Magnetic materials Electron microscopy Differential thermal analysis (DTA)
1. Introduction Hexaferrites have gained great popularity after their discovery by Philips in 1950s [1]. Stable structural and magnetic properties, low-cost manufacturing, cheap raw materials, and electro-
Abbreviations: DTA, Differential thermal analysis; FTIR, Fourier transform infrared spectroscopy; XRD, X-ray diffraction; FESEM, Field emission scanning electron microscopy; EDS, Energy dispersive spectrometer; VSM, Vibrating sample magnetometer. * Corresponding author. E-mail address: [email protected] (Y. Alizad Farzin).
magnetic absorption at hyper frequencies are the main reasons for the utilization of these materials instead of magnetic ferrites. Hexaferrites are divided into six categories according to their crystal structure and chemical formula as follows: M-type or BaFe12O19, W-type or BaMe2Fe16O27, X-type or Ba2Me2Fe28O46, Ytype or Ba2Me2Fe12O22, Z-type or Ba3Me2Fe24O41, and U-type or Ba2Me2Fe36O60, where Me is divalent ion from the first transition series. Hexaferrites can be produced by placing oxygen/(barium or strontium) in various stacking sequences of hexagonal from crystallographic point of view [2]. It has been shown that most of the hexagonal ferrites are hard magnetic materials. However, Y-type hexagonal ferrites exhibit a soft magnetic nature with easy planes
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of magnetization perpendicular to the c-axis at room temperature [3]. Development in the field of communication is currently resulted in moving the operational frequency of electronic devices to gigahertz frequencies [4], which causes a decrease in the demands of conventional soft magnetic materials due to intrinsic restrictions imposed by the occurrence of their natural ferromagnetic resonance at ultra-high frequencies. This technological progress has set off the potential of hexaferrites to replace spinel ferrites in the prospect applications above 1 GHz [2,5]. In recent years, numerous studies have attempted to substitute divalent and trivalent ions and their binary mixtures in order to alter structural and modify electrical and magnetic properties of Ytype hexaferrites. Accordingly, substitution of Me2þ and Fe3þ by other ions such as Al-Ga-In [6], Zn [7], Co-Cu [8], Mg [9], Mn-Tb [10], Pb [11], Sr [12], and Cr [13] has been studied. These dopant ions have been added to Y-type hexaferrites in order to obtain suitable saturation magnetization and coercivity. Clearly, by tailoring the chemical composition and microstructure of the Ytype hexaferrites, it is possible to improve the properties required for specific applications. Also, various preparation methods including solid state reaction [14], hydrothermal [15], solid state reaction [16], microemulsion method [17], co-precipitation [18], citrate precursor technique [19], thermal plasma [20], and sol-gel auto-combustion method [21] have been developed for achieving the desirable properties. An ideal method for preparing hexaferrites has advantages like facile operation, low cast, energy efficiency, short reaction time and temperature, narrow size distribution, and excellent chemical homogeneity. It is reported that solegel auto-combustion method is a suitable technique for the formation of pure hexagonal ferrites with homogeneous particle distribution. Also, it can properly use the heat released from the in-situ reactions between citric acid and nitrate metals to produce some intermediate phases at relatively low temperatures [21]. In this article, the synthesis of nano-crystalline Sr2Co2xMgx/ 2Nix/2Fe12O22 hexaferrite powders (x ¼ 0.0 to 0.6) was considered by a solegel auto-combustion method. During the present investigations, the co-doping of magnetic Ni2þ and nonmagnetic Mg2þcations was chosen to vary the magnetic properties. 2. Materials and methods 2.1. Producing hexaferrite powder Hexaferrite nano-particles with chemical composition of Sr2Co2xMgx/2Nix/2Fe12O22, where x lies between 0.0 and 0.6 with the steps of 0.15, were produced using sol-gel combustion method (citrate precursor method). Fe(NO3)3$9H2O, Co(Cl)2$6H2O, Sr(Cl)2$6H2O, Mg(Cl)2$6H2O, and Ni(Cl)2$6H2O were all used as raw materials. Metal nitrates and citric acid were dissolved in 400 ml of deionized water with 1:1 M ratios to form aqueous solutions with continuous magnetic stirring at 40 C for 4 h. Citric acid was used as a fuel because of having better complexing ability, low ignition temperature (i.e. 200e250 C), and controlled combustion reaction with nitrates. In addition, the chelating agent helped the metal ions to be distributed homogenously [22]. The blended solution was cooled down to room temperature and then concentrated ammonia mix was added to the solution under continuous magnetic stirring condition until the solution became neutral or slightly alkaline (pH 7e8). Stirring process was continued in the neutral environment at 60 C for several hours to stabilize the sol. In order to vaporize 80% distilled water solution, the sol was kept at 80 C for 48 h, where viscous gel, free of any precipitation, was extracted at the end of the process. The solution color at this stage was recorded golden yellow. As the temperature increased to 200 C, the gel
started to combust due to the presence of citric acid. During the combustion process, the gel expanded rapidly and made a loose and fluffy powder [23]. Dried gel was exposed to 400 C for 1 h so that the citric acid could be decomposed completely. The specimens were then calcined at 900 up to 1150 C for 3 h in air with the heating rate of 5 C/min to create Y-type hexaferrite. These specimens were cooled down in the furnace so that the cations fitted at their equilibrium positions. 2.2. Characterization Differential thermal analysis (DTA) behavior of dried gels were investigated using a Linseis thermal analyzer (model L81) from a room temperature up to 1200 C at a heating rate of 10 C/min. Formation of the hexaferrite particles was analyzed by XRD at the ambient temperature in the 2q range of 20 to 70 using Philips Xray diffractometer with CuKa radiation (k ¼ 1.5418 A) and all the reflection peaks were indexed using “X'Pert High Score” (Philips) software. The pellet made of KBr was analyzed to record infrared spectra within the range of 4000 to 400 cm1. This test was carried out using Spectrum 400 FTIR spectrometer (Perkin Elmer). Morphology of the particles was investigated by MIRA3 TESCAN high resolution field emission scanning electron microscopy (FESEM). Magnetic properties of the all samples were investigated by a vibrating sample magnetometer (VSM, model MDK-VSM, Iran) with the maximum applied field of 20 kOe at room temperature. 3. Results and discussion 3.1. Thermal analysis It was observed that the dried gel combusted in a selfpropagating process and completely converted into brownish loose and fluffy powder after burning out. Thermal analysis was carried out to evaluate the mechanism for the formation of hexaferrite phase and to observe the effect of Mg and Ni addition on thermal behavior of the synthesized sample. Fig. 1 shows the differential thermal analysis (DTA) related to nitrate-citrate gels within the temperature range of 25e1200 C, and its characteristics are listed in Table 1. As can be seen in Fig. 1, during the heating of̊ as-prepared samples, various stages such as dehydration of water, decomposition of residual organic groups, and phase formation of hexagonal ferrites were observed. Endothermic peak, within the temperature range of 80e120 C was due to the emerged moisture and emission of water chemical bonds from the specimen [14]. The largest sharp exothermic peak at about 415 C was observed due to the oxidation-reduction reaction between metal nitrate and citric acid ions [24,15]. During the combustion reaction, citric acid ions acted as reluctant and nitrate ions were the oxidizing agent. As a result, nitrate ions not only provided a suitable condition for in-situ oxidization to decompose organic components, but also created a situation for citric acid to act as a fuel. Decomposition of organic components resulted in the large amount of H2O, CO2, and NO2 gases [25]. Relatively broader exothermic peak with the maximum at 520 C might be due to the decomposition of retained unreacted citric acid or nitrates after self-combustion process, but also the decomposition of metal carbonates formed during the reaction [12,26]. The endothermic peak at 640 C might be attributed to starting the transformation of hydroxide to oxide and formation of spinel nickel ferrite (NiFe2O4) and strontium mono ferrite (SrFe2O4) [27]. The exothermic one at 690 C could be due to cobalt spinel (CoFe2O4) formation [15]. Moreover, the exothermic peak observed at 700e750 C range might be attributed to starting the transformation from spinel ferrites structure and strontium mono ferrite
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Fig. 1. DTA measurements for the dried gels with different Mg and Ni content (x).
Table 1 DTA results of dried gel in temperature range of 24e1200 C in heating range of 10 C/min in atmosphere environment. Peak position ( C)
Modality
Characteristic
Ref
80e120 415 520 640 690 700e750 750e950
Endothermic Exothermic Exothermic Endothermic Exothermic Exothermic Fluctuant
Emerged moisture Combustion in citrate-nitrate reaction Decomposition of retained citric acid or nitrates Transformation of hydroxide to oxide Formation of cobalt spinel Formation of M-type hexagonal ferrite Formation of Y-type hexagonal ferrite
[14] [15,24] [12,26] [27] [15] [28,29] [30]
into M-type hexaferrite [28,29]. Fluctuating peaks within the temperature range of 750e950 C might indicate solid-state reactions between different spinel ferrites and M-type hexaferrite to the formation of single phase Y-type hexaferrite [30]. It can be also observed that, in the specimen with x ¼ 0.6, there were no exothermic and endothermic peaks after 800 C which indicated the beginning of the formation of Y-type hexaferrite phase. It demonstrated that, with increasing Mg contents, the temperature of Co2Y hexaferrite formation was decreased. To the best of our knowledge, it may be related to the increasing heat released in self-
propagation reaction, which suppresses the formation of a-Fe2O3 phase and is advantageous in terms of obtaining pure Co2Y hexaferrite phase at a relatively lower temperature [31]. 3.2. FT-IR studies The room temperature infrared spectra of Y-type hexaferrites are shown in Fig. 2. Spectra of the investigated samples measured in the frequency range of 4000e400 cm1 could be used to observe chemical and structural changes and presence of different crystal
100
% Transmittance
90 100
80 X = 0.0 X = 0.15 X = 0.3 X = 0.45 X = 0.6
70 60
80 60
50 40 4000
40
3600
3200
2800
2400
2000
650 600 550 500 450 400
1600
1200
800
400
Wave Numbers (Cm-1) Fig. 2. Infrared spectroscopy results of the calcined samples at 1000 C.
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Table 2 FT-IR spectroscopic data of sol-gel derived oxalate after calcinated at 1000 C for 3 h in air. Peak position (cm1)
Intensity
Vibrational mode(s)
Ref
3435 1633 1439 592 464
Strong Weak Weak Strong Medium
Surface hydroxyl group (eOH) Surface hydroxyl group (eOH) NeO stretching vibration of NO3 Oxygen and metal cations of octahedral site Oxygen and metal cations on tetrahedral sites
[9,26] [9,26] [33] [34,35] [34,35]
phases in the materials during calcination process. The spectra were quite similar for all the compositions and values of the absorption bands are summarized in Table 2. The results showed good agreement with the data reported in the literature [32]. The broad absorption band in 3435 cm1 and 1633 cm1 was the results of stretching and bending bands of the surface hydroxyl group (eOH) of magnetic particles acquired from wet atmosphere during calcination [9,26]. For the samples with x ¼ 0.0 and 0.15, the very low intensity absorption band at 1439 cm1 could be attributed to the anti-symmetric stretching vibration of NO 3 , indicating that nitrate ions are present in the calcined samples [33]. As seen in Fig. 2, with an increase of Mg due to enhancing self-propagation reaction heat in x > 0.15, vibration bands of nitrate functional group disappeared due to the decomposition of nitride ions. Absorption spectra of calcined samples showed two distinct peaks in low frequency region which were identified as the metal-oxygen stretching vibrations of hexaferrite [3]. The highest peaks in the range of 554e592 cm1 were attributed to the intrinsic vibration of octahedral sites, whereas the lowest peak observed at 433 cm1 showed the characteristic interaction between oxygen and metal cations of tetrahedral sites [34,35]. It was expected to see differences in the intensity of the bands in various compositions because of the difference in the amount of divalent cations in octahedral and tetrahedral sites. These two bands are the characteristics bands of all ferrites. As reported earlier [36], these bands are the evidence of the formation of the metal ions-oxygen bands in the hexagonal. The difference in the cation mass, cation-oxygen distance, and bonding forces could be responsible for the difference in the wavelength of bands for the calcined samples [36,37].
Fig. 3. XRD patterns of the samples calcined at 900 C for 3 h.
3.3. Phase identification Based on the results of DTA studies, the crystallization process of the dried gel of Y-type hexaferrite in the temperature range of
Fig. 4. XRD patterns of the samples calcined at 950 C for 3 h.
Fig. 5. XRD patterns of substituted Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1000 C for 3 h.
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900e1150 C was emphatically investigated. The X-ray diffraction of calcined specimens at 900 C for 3 h is shown in Fig. 3. This figure reveals that the powders calcined at this temperature contained strontium hexaferrite (JCPDS Card no. 00-024-1207) as the major and minor phases of hematite (JCPDS Card no. 01-073-0603), magnetite (JCPDS Card no. 00-003-0863), SrO (JCPDS Card no. 00001-0886), and spinel ferrites (JCPDS Card no. 00-001-1121, 00003-0875 and 01-071-1232). Also, the single phase Co2Y could not be obtained directly from the simple oxides due to the complexity of crystal structure and is usually produced from some intermediate phases formed at lower temperatures [16]. During the fabrication of Y-type hexaferrite, in fact, a set of chemical reactions has been done, which can be described by the following equations [30]:
Fig. 6. XRD patterns of substituted Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1150 C for 3 h.
gel þ g-Fe2O3 (burned gel as a precursor)
(1)
g-Fe2O3 þ SrO / SrFe2O4 (spinel ferrite)
(2)
SrFe2O4 þ 5g-Fe2O3 / SrFe12O19 (M-type hexaferrite)
(3)
SrFe12O19 þ 6g-Fe2O3 þ 3SrO þ 4CoO / 2Sr2Co2Fe12O22 (Y-type hexaferrite) (4) Based on the above equations, the citrate-nitride gels presented
Fig. 7. FESEM micrographs of the samples calcined at 950 C: (a) x ¼ 0.0, (b) x ¼ 0.3, (c) x ¼ 0.6.
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self-propagation combustion behavior and none of them could be converted directly into the Y-type hexagonal crystal phase during combustion. When the samples were heated at 450 C, the gel was transformed into the intermediate phase g-Fe2O3, which had a cubic spinel structure with chemical formula Fe6O2þ 8 (similar to S block in M-type and Y-type hexaferrite) via dehydration and decomposition. g-Fe2O3 reacted easily with SrO to form SrFe2O4 and then further reacted with SrFe2O4 to form SrFe12O19 at lower temperature. With increasing the calcination temperature, SrFe12O19 reacted with g-Fe2O3, CoO, and SrO to form single-phase Sr2Co2Fe12O22. Indeed, Reaction (4) indicates that, with the improvement of calcination temperature, strontium hexaferrite, spinel ferrite, and SrO reacted together and were gradually transformed into Co2Y. In comparison with the standard Y-type hexaferrite (JCPDS Card no. 01-082-0472), it can be seen that, in the samples calcined at 950 C for x ¼ 0.0 and 0.3 (Fig. 4), the powders consisted of Y-type hexaferrites along with the presence of a small amount of secondary phases such as hematite, SrO, and CoFe2O4. Also, with increasing the Mg and Ni contents at x ¼ 0.6, the peaks corresponding to impurity phases apparently disappeared. It means that increasing Mg content decreased the phase formation temperature of Y-type hexaferrite. When calcination temperature was raised to 1000 C (Fig. 5), it can be seen that all of the diffraction patterns matched strongly with the standard patterns of JCPDS Card no. 01-082-0472 and no
unreacted components were present in the final product. Crystallite size of all the calcined samples was calculated using Scherrer's equation and found to be 45e63 nm. Even though the calcination temperature was reached up to 1100 C, no diffraction patterns change was observed. Similar results have been demonstrated in such works on Y-type hexaferrites [34,38]. Furthermore, at 1150 C (Fig. 6), single phase Co2Y starts to decompose into the previous intermediate phases again. 3.4. Morphology and grain size Microstructures of all the calcined specimens at different temperature were studied using field emission scanning electron microscopy (FESEM). Figs. 7e9 display the representative FESEM micrographs of Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite (where x ¼ 0.0, 0.3, and 0.6) calcined at temperatures between 950 and 1050 C for 3 h in the air atmosphere. As can be seen in Fig. 7 (a, b, and c), the amount of the intermediate phases such as spinel ferrites, SrO, and M-type hexaferrite identified by XRD analysis decreased as MgNi contents increased, while the major phase (Y-type hexaferrite) with hexagonal plate like morphology increased. After the substitution of divalent cations at x ¼ 0.6, the intermediate phases completely disappeared and only hexagonal-shaped Co2Y was obtained. The reduction of intermediate phases at higher x values can be attributed to the
Fig. 8. FESEM micrographs of the Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1000 C: (a) x ¼ 0.0, (b) x ¼ 0.3, (c) x ¼ 0.6.
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effect of dopants, particularly Mg2þ ions, on the heat of autocombustion reaction. This result was in good agreement with DTA data, in which after 800 C, with increasing Mg2þ contents, this curve became smooth and no endothermic and exothermic peaks
7
were observed at x ¼ 0.6, which can be interpreted as decreasing the formation temperature of Y-type hexaferrite. As shown in Fig. 8 (a, b, and c), when temperature increased to 1000 C, due to the reaction of retained M-type hexaferrite with other intermediate
Fig. 9. FESEM micrographs of the Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1050 C: (a) x ¼ 0.0, (b) x ¼ 0.3, (c) x ¼ 0.6.
Fig. 10. FESEM micrographs of the Sr2Co2xMgx/2Nix/2Fe12O22 (x ¼ 0.3) hexaferrite samples calcined at 1150 C.
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phases, the single phase of Y-type hexaferrite was obtained in all the samples [34]. It can be considered that the Y-type hexaferrites at 1000 C showed well defined hexagonal platelet like shapes with an almost uniform particle size distribution. Moreover, the thickness of the particle as calculated using Image J software was smaller for the ferrites substituted with higher values of Ni2þ and Mg2þ ions (40 nm) than those of pure hexaferrite (110 nm). Shape of the grains is very important for specific applications in different fields and it has been reported that the platelet-shaped hexaferrite can be used as microwave absorbing coatings [2]. Mean size of the particles increased with the increase of calcination temperature. As temperature increased to 1050 C (Fig. 9aec), thickness of the hexagonal flakes for x ¼ 0.0, 0.3, and 0.6 increased to about 257, 248, and 231 nm, respectively. Further, particle growth and neck formation were due to the promotion of diffusion mechanisms at higher temperatures. It could be also observed that, with the further increase of temperature to 1150 C (Fig. 10), some impurities were seen on the surface of hexagonal flakes, probably due to the decomposition of Co2Y particles into some previous intermediate phases like Fe3O4 and SrFe12O19 confirmed by EDS analysis (Fig. 11). In addition, it has been reported that, with increasing the calcination temperature, the tendency of the particles for joining together is enhanced and large particles (2.3 mm) with hexagonal pyramidal shape are generated [27,39]. 3.5. Magnetic properties The magnetic hysteresis loops for Y-type hexaferrites calcined at temperatures from 950 C to 1150 C are shown in Figs. 12 and 13. Magnetic properties such as coercivity (Hc), saturation magnetization (Ms), remanence (Mr), and squareness ratio (Mr/Ms) were measured at 20 kOe and summarized in Table 3. Width of the loops showed that all of the samples had small coercivity and were relatively soft hexaferrites. Fig. 12 demonstrates the hysteresis loops of the samples with x ¼ 0.3 calcined at 950 to 1150 C. Values of saturation magnetization (Ms), remanence (Mr), and coercivity for all the samples were found to be in the range of (30.00e56.12) emu/g, (10.62e22.98) emu/g, and (250e1140) Oe, respectively. They were very close to typical values reported for nanostructured Y-type hexaferrites [40]. It is clear that, with the increase in the calcination temperature from 950 to 1000 C, Ms and Mr were increased significantly (due to the removing of intermediate phases) and remained constant with further increase of temperature to 1100 C and then decreased at 1150 C. The latter reduction of the magnetization values can be the result of hexaferrite decomposition at higher temperatures as confirmed by XRD patterns. Also, values of coercivity decreased continuously from 1140 to 250 Oe with increasing the calcination temperature from 900 to 1150 C. It is well known that the size of particles has a significant effect on the coercivity of hexaferrite. This typical behavior is attributable to the transition from single to multi domain structures, which occurs with increasing grain size at higher temperatures [41]. Critical size of a single domain particle for Y-type hexaferrite is reported to about 1.18 mm [34,42,43]. When the particle size becomes bigger than the critical value, most of them would exist in a multi domain state. As shown in FESEM micrographs (Figs. 7e10), with an increase in the calcination temperature, the particle size also increased significantly. As the particles became larger than the single domain size, value of coercivity decreased noticeably to 250 Oe. Similar results have been also observed in the recent studies for strontium and barium hexaferrites [44,45]. On the basis of these results, it is obvious that, in our case, the coercivity of hexaferrites can be controlled greatly by calcinating temperature and thus by grain size. It is known that hexaferrites which have low coercivity are useful for security,
Fig. 11. EDS spectrum of the calcined samples at 1150 (b) SrFe12O19, (c) Fe3O4.
C:
(a) Sr2Co2xMgx/2Nix/
2Fe12O22,
switching, microwave devices, and especially high frequency applications [12]. Fig. 13 shows the hysteresis loops of the samples with x ¼ 0.0 and 0.6 calcined at 950 C, where the values of saturation magnetization were found to be 30 and 51 emu/g, respectively. Magnetic behavior of these samples can be described according to the effect of magnesium contents on the formation of Y-type hexaferrite from intermediate phases (as discussed in Section 3.3). The results showed that the saturation magnetization of undoped hexaferrite (x ¼ 0.0) a much less than the values reported in
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9
60 24
45
20 16 12
15 0 -15
)
Magnetization (emu/g)
30
(a) (b) (c) (d) (e)
)
-30 -45 400
-60 -20000 -16000 -12000
-8000
-4000
0
4000
8000
800
1200
12000
16000
20000
Applied Field (Oe) Fig. 12. Magnetic hysteresis loops of Sr2Co2xMgx/2Nix/2Fe12O22 (x ¼ 0.3) hexaferrite samples calcined at (a) 950 C, (b) 1000 C, (c) 1050 C, (d) 1100 C, (e) 1150 C.
60 24
45 18 12
)
Magnetization (emu/g)
30 15 0
(a) (b)
)
-15 -30 -45
1100 1200 1300
-60 -20000 -16000 -12000
-8000
-4000
0
4000
8000
12000
16000
20000
Applied Field (Oe) Fig. 13. Magnetic hysteresis loops of calcined samples at 950 C for (a) x ¼ 0.0 and (b) x ¼ 0.6.
recent studies (about 59 emu/g) [45]. As confirmed from XRD pattern of un-substituted specimen in Fig. 4a, it can be due to the dilution of the strontium hexaferrite by the secondary phase (hematite) which is a weak ferromagnetic material at room temperature with Ms~ 0.8 emu/g at 18 kOe [46e49]. Also, the effects of SrO can be neglected, as it is diamagnetic. In addition, Fig. 13b shows that the saturation magnetization increased to 51.25 emu/g with increasing Mg content (x ¼ 0.6). Again, it could be attributed to the influence of Mg addition on the formation of Y-type hexaferrite and removing the intermediate phases. Also, Fig. 13a demonstrates that the coercivity of undoped hexaferrite (x ¼ 0.0) was much less than the values reported for pure strontium hexaferrite (about 5000 Oe)
[45,32]. High coercivity of pure strontium hexaferrite was due to strong uniaxial anisotropy along the c-axis of M-type hexaferrite. But, doping of Co, Ni, and especially Mg in strontium hexaferrite led to a rapid decrease in coercivity. The result could be attributed to the reduction in the crystal anisotropy field due to the change of the easy-axis of magnetization from the c-axis to the basal plane [50]. 4. Conclusion 1 Nano-crystalline and single phase Mg-Ni doped Sr2Co2xMgx/ 2Nix/2Fe12O22 (Co2Y) hexaferrites (space group R3/m) with the average crystallite size in the range of 45e63 nm were
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Table 3 Effects of calcination temperature on saturation magnetization (Ms), remanence magnetization (Mr), squareness and coercivity (Hc) of Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite (x ¼ 0.3 and 0.6). Sample (x)
Temperature ( C)
Ms (emu/g)
Mr (emu/g)
Squareness
Hc (Oe)
0.3 0.6 0.3 0.3 0.3 0.3
950 950 1000 1050 1100 1150
30.00 51.25 56.12 56.00 55.53 50.06
13.30 22.01 22.98 22.46 19.11 10.62
0.44 0.43 0.41 0.40 0.34 0.21
1140 1230 950 900 634 250
successfully synthesized via the auto-combustion sol-gel technique followed by calcinations at temperatures between 950 and 1100 C. 2 The X-ray diffraction patterns revealed the formation of single phase Y-type hexaferrite at temperature of 950 C for the sample with x ¼ 0.6, while additional impurity phases such as a-Fe2O3 and SrO were observed in the samples with x ¼ 0.0 and 0.3. 3 From FESEM micrographs, it can be concluded that hexaferrite particles with well-defined platelet hexagonal shapes were synthesized and the thickness of the particles was decreased with increasing Mg2þ content. 4 Magnetization measurements demonstrated that the presence of SrO and weak ferromagnetic a-Fe2O3 beside Co2Y hexaferrite in the final product reduced the magnetization from 56 to 30 emu/g. The saturation magnetization values did not show any considerable changes, whereas coercivity was strongly decreased from 950 to 250 Oe by increasing the calcination temperatures. Based on above characteristics, it can be concluded that the synthesized hexaferrites can be promising candidates for very high frequency applications ranged from 900 MHz to 3 GHz. Acknowledgment The authors would like to thank the Iranian Nanotechnology Initiative Council (Grant no. 45519) for providing us with financial support in this project. References [1] G.H. Jonker, H.P.J. Wijn, P.B. Braum, Magnetic and microwave absorbing properties of m-type hexaferrites substituted by Ru-Co (BaFe122xRuxCoxO19), Philips Tech. Rev. 18 (1956) 145. [2] R.C. Pullar, Hexagonal ferrites: a review of the synthesis, properties and applications of hexaferrite ceramics, Prog. Mater. Sci. 57 (2012) 1191e1334. [3] G. Murtaza, R. Ahmad, T. Hussain, R. Ayub, I. Ali, M.A. Khan, M.N. Akhtar, Structural and magnetic properties of NdeMn substituted Y-type hexaferrites synthesized by microemulsion method, J. Alloy. Compd. 602 (2014) 122e129. [4] J. Kulikowski, Magnetostrictive properties of Cox(NiZn)1xFe2O4 ferrites in the case of small changes of iron content, J. Magn. Magn. Mater. 41 (1984) 56. [5] M. Irfana, M.U. Islam, I. Ali, M.A. Iqbal, N. Karamat, H.M. Khan, Effect of Y2O3 doping on the electrical transport properties of Sr2MnNiFe12O22 Y-type hexaferrite, Curr. Appl. Phys. 14 (2014) 112e117. [6] J.T. Lim, C.M. Kim, B.W. Lee, C.S. Kim, Investigation of magnetic properties of non-magnetic ion (Al, Ga, In) doped Ba2Mg0.5Co1.5Fe12O22, J. Appl. Phys. 111 (2012), 07A518. [7] A.M. Abo El Ata, S.M. Attia, Dielectric dispersion of Y-type hexaferrites at low frequencies, J. Magn. Magn. Mater. 257 (2003) 165e174. [8] Y. Bai, J. Zhou, Z. Gui, L. Li, Phase formation process, microstructure and magnetic properties of Y-type hexagonal ferrite prepared by citrate solegel auto-combustion method, Mater. Chem. Phys. 98 (2006) 66e70. [9] A. Elahi, M. Ahmad, I. Ali, M.U. Rana, Preparation and properties of solegel synthesized Mg-substituted Ni2Y hexaferrites, J. Ceram. Int. 39 (2013) 983e990. [10] I. Ali, M.U. Islam, M.N. Ashiq, M.A. Iqbal, H.M. Khan, N. Karamat, Effect of TbeMn substitution on DC and AC conductivity of Y-type hexagonal ferrite, J. Alloy. Compd. 579 (2013) 576e582. es, [11] G.F.M. Pires Júniora, H.O. Rodrigues, J.S. Almeida, E.O. Sancho, J.C. Go M.M. Costa, J.C. Denardin, A.S.B. Sombra, Study of the dielectric and magnetic properties of Co2Y, Y-type hexaferrite (Ba2Co2Fe12O22) added with PbO and Bi2O3in the RF frequency range, J. Alloy. Compd. 493 (2010) 326e334.
[12] M. Ahmad, Q. Ali, I. Ali, I. Ahmad, M.A. Khan, M.N. Akhtar, G. Murtaza, M.U. Rana, Effects of Sr-substitution on the structural and magnetic behavior of Ba-based Y-type hexagonal ferrites, J. Alloy. Compd. 580 (2013) 23e28. [13] M.J. Iqbal, F. Liaqat, Physical and electrical properties of nanosized Mn- and Cr-Doped strontium Y-Type hexagonal ferrites, J. Am. Ceram. Soc. 93 (2010) 474e480. [14] M.J. Iqbal, M.N. Ashiq, P.H. Gomez, J.M. Munoz, Influence of annealing temperature and doping rate on the magnetic properties of ZreMn substituted Srhexaferrite nanoparticles, J. Alloy. Compd. 500 (2010) 113e116. [15] M.M. Rashad, M. Rasly, H.M. El-Sayed, A.A. Sattar, I.A. Ibrahim, Controlling the composition and the magnetic properties of hexagonal Co2Z ferrite powders synthesized using two different methods, J. Appl. Phys. A 112 (2012) 963e973. [16] Y. Bai, J. Zhou, Z. Gui, L. Li, An investigation of the magnetic properties of Co2Y hexaferrite, J. Mater. Lett. 57 (2002) 807e811. [17] I. Ali, M.U. Islam, M.N. Ashiq, M.A. Iqbal, H.M. Khan, G. Murtaza, Role of grain boundaries in the conduction of EueNi substituted Y-type hexaferrites, J. Magn. Magn. Mater. 362 (2014) 115e121. [18] H.I. Hsiang, R.Q. Yao, Synthesis of 3BaO.2CoO.12Fe2O3 powder using chemical co-precipitation, J. Magn. Magn. Mater. 307 (2006) 273e278. [19] M. Rasly, M.M. Rashad, Structural and magnetic properties of SneZn doped BaCo2Z-type hexaferrite powders prepared by citrate precursor method, J. Magn. Magn. Mater. 338 (2013) 58e64. gard, K. Bobzin, G. Bolelli, A. Hujanen, P. Lintunen, D. Lisjak, S. Gyergyek, [20] M. Be €fer, T. Varis, Thermal spraying of L. Lusvarghi, M. Pasquale, K. Richardt, T. Schla Co,Ti-substituted Ba-hexaferrite coatings for electromagnetic wave absorption applications, Surf. Coat. Technol. 203 (2009) 3312e3319. [21] M. Ahmada, R. Grossinger, M. Kriegisch, F. Kubel, M.U. Rana, Characterization of Sr-substituted W-type hexagonal ferrites synthesized by solegel autocombustion method, J. Magn. Magn. Mater. 332 (2013) 137e145. [22] V.N. Dhage, M.L. Mane, A.P. Keche, C.T. Birajdar, K.M. Jadhav, Structural and magnetic behaviour of aluminium doped barium hexaferrite nano particles synthesized by solution combustion technique, Phys. B Condens. Matter 406 (2011) 789. [23] M.C. Dimri, A. Verma, S.C. Kashyap, D.C. Dube, O.P. Thakur, C. Prakash, Structural, dielectric and magnetic properties of NiCuZn ferrite grown by citrate precursor method, J. Mater. Sci. Eng. B 133 (2006) 42. [24] M.M. Rashad, M. Rasly, H.M. El-Sayed, A.A. Sattar, I.A. Ibrahim, Controlling the composition and the magnetic properties of hexagonal Co2Z ferrite powders synthesized using two different methods, Appl. Phys. A 112 (2013) 963e973. [25] A. Mali, A. Ataie, Influence of the metal nitrates to citric acid molar ratio on the combustion process and phase constitution of barium hexaferrite particles prepared by solegel combustion method, Ceram. Int. 30 (2004) 1979. €ssinger, M. Kriegisch, F. Kubel, M.U. Rana, Magnetic and [26] M. Ahmada, R. Gro microwave attenuation behavior of Al-substituted Co2W hexaferrites synthesized by sol-gel autocombustion process, Curr. Appl. Phys. 12 (2012) 1413e1420. [27] S. Tyagi, H.B. Baskey, R.C. Agarwala, V. Agarwala, Development of hard/soft ferrite nanocomposite for enhanced microwave absorption, J. Ceram. Int. 37 (2011) 2631e2641. [28] H.I. Hsiang, R.Q. Yao, Formation mechanism of 3BaO$2CoO$12Fe2O3 powder synthesized using chemical co-precipitation, J. Alloy. Compd. 453 (2008) 366e370. [29] H.I. Hsiang, R.Q. Yao, Hexagonal ferrite powder synthesis using chemical coprecipitation, Mater. Chem. Phys. 104 (2007) 1e4. [30] X.F. Yang, Q. Jin, Z.P. Chen, Q.L. Li, B. Liu, Fabrication and microwave absorbent properties of Cobate zinc substituted W-type BaCoZnFe16O27, J. Magn. Magn. Mater. 367 (2014) 64e68. [31] C.J. Li, B. Wang, J.N. Wang, Magnetic and microwave absorbing properties of electrospun Ba(1x)LaxFe12O19Nanofibers, J. Magn. Magn. Mater. 324 (2012) 1305e1311. [32] S.K. Chawla, R.K. Mudsainiyan, S.S. Meena, S.M. Yusuf, Solegel synthesis, structural and magnetic properties of nanoscale M-type barium hexaferrites BaCoxZrxFe(122x)O19, J. Magn. Magn. Mater. 350 (2014) 23e29. [33] A. Ghasemi, Development of uniaxial magnetocrystalline anisotropy in SrFe12x(DyGd)xO19 thin film synthesized by incorporation of high coercivity nanoparticles in solegel method, J. Magn. Magn. Mater. 361 (2014) 112e117. [34] C. Zhang, J. Shi, X. Yang, L. De, X. Wang, Effects of calcination temperature and solution pH value on the structural and magnetic properties of Ba2Co2Fe12O22 ferrite via EDTA-complexing process, J. Mater. Chem. Phys. 123 (2010)
Please cite this article in press as: Y. Alizad Farzin, et al., Synthesis behavior and magnetic properties of Mg-Ni co-doped Y-type hexaferrite prepared by sol-gel auto-combustion method, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.04.082
Y. Alizad Farzin et al. / Materials Chemistry and Physics xxx (2016) 1e11 551e556. [35] A. Aslama, M.U. Islama, I. Alia, M.S. Awanb, M. Irfana, A. Iftikhar, High frequency electrical transport properties of CoFe2O4 and Sr2NiMnFe12O22 composite ferrites, J. Ceram. Int. 40 (2014) 155e162. € ssinger, M. Kriegisch, F. Kubel, M.U. Rana, Effects of [36] M. Ahmada, I. Ali, R. Gro divalent ions substitution on the microstructure, magnetic and electromagnetic parameters of Co2W hexagonal ferrites synthesized by solegel method, J. Alloy. Compd. 579 (2013) 57e64. [37] M.J. Iqbal, B. Ain, Synthesis and study of physical properties of Zr4þeCo2þ codoped barium hexagonal ferrites, Mater. Sci. Eng. B 164 (2009) 6e11. [38] Y. Alizad Farzin, O. Mirzaee, A. Ghasemi, Influence of Mg and Ni substitution on structural, microstructural and magnetic properties of Sr2Co2xMgx/2Nix/ 2Fe12O22 (Co2Y) hexaferrite, J. Magn. Magn. Mater. 371 (2014) 14e19. [39] Z. Mosleh, P. Kameli, M. Ranjbar, H. Salamati, Effect of annealing temperature on structural and magnetic properties of BaFe12O19 hexaferrite nanoparticles, Ceram. Int. 40 (2014) 7279e7284. [40] J. Jalli, Y.K. Hong, S. Bae, J.J. Lee, G.S. Abo, J.H. Park, B.C. Choi, T. Mewes, S.G. Kim, S.H. Gee, I.T. Nam, T. Tanaka, Magnetic and microwave properties of ferromagnetic Zr-substituted Ba2Zn2Fe12O22 (Zn-Y) single crystals, J. Appl. Phys. 109 (2011), 07A509. € zeri, Z. Durmus, A. Baykal, E. Uysal, Preparation of high quality, single [41] H. So domain BaFe12O19 particles by the citrate solegel combustion route with an initial Fe/Ba molar ratio of 4, Mater. Sci. Eng. B 177 (2012) 949e955. [42] C. Sudakar, G.N. Subbanna, T.R.N. Kutty, Wet chemical synthesis of multicomponent hexaferrites by gel to crystallite conversion and their magnetic properties, J. Magn. Magn. Mater. 263 (2003) 253e268.
11
[43] Z.F. Zi, Y.P. Sun, X.B. Zhu, Z.R. Yang, J.M. dai, W.H. Song, Structural and magnetic properties of SrFe12O19 hexaferrite synthesized by a modified chemical coprecipitation method, J. Magn. Magn. Mater. 320 (2008) 2746e2751. [44] M. Ahmad, I. Ali, F. Aen, M.U. Islam, M.N. Ashiq, S. Atiq, W. Ahmad, M.U. Rana, Effect of sintering temperature on magnetic and electrical properties of nanosized Co2W hexaferrites, Ceram. Int. 38 (2012) 1267e1273. [45] H. Luo, B.K. Rai, S.R. Mishra, V.V. Nguyen, J.P. Liu, Physical and magnetic properties of highly aluminum doped strontium ferrite nanoparticles prepared by auto-combustion route, J. Magn. Magn. Mater. 324 (2012) 2602e2608. [46] H. Ashima, S. Sanghi, A. Agarwal, D. Reetu, Rietveld refinement, electrical properties and magnetic characteristics of CaeSr substituted barium hexaferrites, J. Alloy. Compd. 513 (2012) 436e444. [47] T. Tsutaoka, N. Koga, Magnetic phase transitions in substituted barium ferrites BaFe12x(Ti0.5Co0.5)xO19 (x ¼ 0e5), J. Magn. Magn. Mater. 325 (2013) 36e41. nchez-De Jesús, A.M. Bolarín-Miro , C.A. Corte s-Escobedo, R. Valenzuela, [48] F. Sa S. Ammar, Mechanosynthesis, crystal structure and magnetic characterization of M-type SrFe12O19, Ceram. Int. 40 (2014) 4033e4038. [49] M. Tadic, N. Citakovic, M. Panjan, B. Stanojevic, D. Markovic, D. Jovanovic, V. Spasojevic, Synthesis, morphology and microstructure of pomegranate-like hematite (a-Fe2O3) superstructure with high coercivity, J. Alloy. Compd. 543 (5) (2012) 118e124. [50] A. Sharbati, J. Molaverdi Khani, G.R. Amiri, Microwave absorption studies of nanocrystalline SrMnx/2(TiSn)x/4Fe12xO19 prepared by the citrate solegel method, Solid State Commun. 152 (2012) 199e203.
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Synthesis behavior and magnetic properties of Mg-Ni co-doped Y-type hexaferrite prepared by sol-gel auto-combustion method Y. Alizad Farzin a, *, O. Mirzaee b, A. Ghasemi c a
School of Metallurgy and Materials Engineering, College of Engineering, University of Tehran, P.O. Box 14395-553, Tehran, Iran Department of Materials Science and Engineering, University of Semnan, Iran c Department of Materials Engineering, Malek Ashtar University of Technology, Iran b
h i g h l i g h t s Nano crystalline Y-type hexaferrites has been synthesized via sol-gel auto combustion method. Effect of Ni and Mg ions on synthesis behavior and magnetic properties of Co2Y hexaferrite was investigated. Thermal behavior of Mg ions caused reduction in synthesis temperature to 950 C. Average thickness of particles has been decreased by the increase of Mg and Ni ions. The coercivity strongly decreased with increasing of calcination temperature.
a r t i c l e i n f o
a b s t r a c t
Article history: Received 17 October 2014 Received in revised form 13 April 2016 Accepted 25 April 2016 Available online xxx
Nano crystalline Y-type hexaferrites with chemical composition of Sr2Co2xMgx/2Nix/2Fe12O22 (x of 0 e0.6) were prepared by sol-gel auto-combustion technique at the temperature ranging from 900 to 1150 C. The prepared samples were characterized by differential thermal analysis (DTA), Fourier transform infrared spectroscopy (FTIR), X-ray diffraction (XRD), field emission scanning electron microscopy (FESEM), energy dispersive spectrometer (EDS), and vibrating sample magnetometer (VSM). The results demonstrated that single phase co-doped Y-type hexaferrites with space group of R3/m were prepared at 1000 C and crystallite size of the samples was calculated in the range of 45e63 nm. Also, below this temperature, some intermediate phases such as hematite, spinel ferrite, and SrO were observed. All of the synthesized hexaferrites showed homogeneous distribution and hexagonal plateletlike shapes which were suitable for microwave absorption. Hysteresis loop measurements revealed that the presence of hematite as a second phase caused a reduction in the saturation magnetization. Moreover, it was observed that, with increasing the calcination temperature to above 1000 C, saturation magnetization demonstrated no significant changes while coercivity reduced from 950 to 250 Oe, which was due to transition from single to multi domain structures. © 2016 Elsevier B.V. All rights reserved.
Keywords: Nanostructures Magnetic materials Electron microscopy Differential thermal analysis (DTA)
1. Introduction Hexaferrites have gained great popularity after their discovery by Philips in 1950s [1]. Stable structural and magnetic properties, low-cost manufacturing, cheap raw materials, and electro-
Abbreviations: DTA, Differential thermal analysis; FTIR, Fourier transform infrared spectroscopy; XRD, X-ray diffraction; FESEM, Field emission scanning electron microscopy; EDS, Energy dispersive spectrometer; VSM, Vibrating sample magnetometer. * Corresponding author. E-mail address: [email protected] (Y. Alizad Farzin).
magnetic absorption at hyper frequencies are the main reasons for the utilization of these materials instead of magnetic ferrites. Hexaferrites are divided into six categories according to their crystal structure and chemical formula as follows: M-type or BaFe12O19, W-type or BaMe2Fe16O27, X-type or Ba2Me2Fe28O46, Ytype or Ba2Me2Fe12O22, Z-type or Ba3Me2Fe24O41, and U-type or Ba2Me2Fe36O60, where Me is divalent ion from the first transition series. Hexaferrites can be produced by placing oxygen/(barium or strontium) in various stacking sequences of hexagonal from crystallographic point of view [2]. It has been shown that most of the hexagonal ferrites are hard magnetic materials. However, Y-type hexagonal ferrites exhibit a soft magnetic nature with easy planes
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of magnetization perpendicular to the c-axis at room temperature [3]. Development in the field of communication is currently resulted in moving the operational frequency of electronic devices to gigahertz frequencies [4], which causes a decrease in the demands of conventional soft magnetic materials due to intrinsic restrictions imposed by the occurrence of their natural ferromagnetic resonance at ultra-high frequencies. This technological progress has set off the potential of hexaferrites to replace spinel ferrites in the prospect applications above 1 GHz [2,5]. In recent years, numerous studies have attempted to substitute divalent and trivalent ions and their binary mixtures in order to alter structural and modify electrical and magnetic properties of Ytype hexaferrites. Accordingly, substitution of Me2þ and Fe3þ by other ions such as Al-Ga-In [6], Zn [7], Co-Cu [8], Mg [9], Mn-Tb [10], Pb [11], Sr [12], and Cr [13] has been studied. These dopant ions have been added to Y-type hexaferrites in order to obtain suitable saturation magnetization and coercivity. Clearly, by tailoring the chemical composition and microstructure of the Ytype hexaferrites, it is possible to improve the properties required for specific applications. Also, various preparation methods including solid state reaction [14], hydrothermal [15], solid state reaction [16], microemulsion method [17], co-precipitation [18], citrate precursor technique [19], thermal plasma [20], and sol-gel auto-combustion method [21] have been developed for achieving the desirable properties. An ideal method for preparing hexaferrites has advantages like facile operation, low cast, energy efficiency, short reaction time and temperature, narrow size distribution, and excellent chemical homogeneity. It is reported that solegel auto-combustion method is a suitable technique for the formation of pure hexagonal ferrites with homogeneous particle distribution. Also, it can properly use the heat released from the in-situ reactions between citric acid and nitrate metals to produce some intermediate phases at relatively low temperatures [21]. In this article, the synthesis of nano-crystalline Sr2Co2xMgx/ 2Nix/2Fe12O22 hexaferrite powders (x ¼ 0.0 to 0.6) was considered by a solegel auto-combustion method. During the present investigations, the co-doping of magnetic Ni2þ and nonmagnetic Mg2þcations was chosen to vary the magnetic properties. 2. Materials and methods 2.1. Producing hexaferrite powder Hexaferrite nano-particles with chemical composition of Sr2Co2xMgx/2Nix/2Fe12O22, where x lies between 0.0 and 0.6 with the steps of 0.15, were produced using sol-gel combustion method (citrate precursor method). Fe(NO3)3$9H2O, Co(Cl)2$6H2O, Sr(Cl)2$6H2O, Mg(Cl)2$6H2O, and Ni(Cl)2$6H2O were all used as raw materials. Metal nitrates and citric acid were dissolved in 400 ml of deionized water with 1:1 M ratios to form aqueous solutions with continuous magnetic stirring at 40 C for 4 h. Citric acid was used as a fuel because of having better complexing ability, low ignition temperature (i.e. 200e250 C), and controlled combustion reaction with nitrates. In addition, the chelating agent helped the metal ions to be distributed homogenously [22]. The blended solution was cooled down to room temperature and then concentrated ammonia mix was added to the solution under continuous magnetic stirring condition until the solution became neutral or slightly alkaline (pH 7e8). Stirring process was continued in the neutral environment at 60 C for several hours to stabilize the sol. In order to vaporize 80% distilled water solution, the sol was kept at 80 C for 48 h, where viscous gel, free of any precipitation, was extracted at the end of the process. The solution color at this stage was recorded golden yellow. As the temperature increased to 200 C, the gel
started to combust due to the presence of citric acid. During the combustion process, the gel expanded rapidly and made a loose and fluffy powder [23]. Dried gel was exposed to 400 C for 1 h so that the citric acid could be decomposed completely. The specimens were then calcined at 900 up to 1150 C for 3 h in air with the heating rate of 5 C/min to create Y-type hexaferrite. These specimens were cooled down in the furnace so that the cations fitted at their equilibrium positions. 2.2. Characterization Differential thermal analysis (DTA) behavior of dried gels were investigated using a Linseis thermal analyzer (model L81) from a room temperature up to 1200 C at a heating rate of 10 C/min. Formation of the hexaferrite particles was analyzed by XRD at the ambient temperature in the 2q range of 20 to 70 using Philips Xray diffractometer with CuKa radiation (k ¼ 1.5418 A) and all the reflection peaks were indexed using “X'Pert High Score” (Philips) software. The pellet made of KBr was analyzed to record infrared spectra within the range of 4000 to 400 cm1. This test was carried out using Spectrum 400 FTIR spectrometer (Perkin Elmer). Morphology of the particles was investigated by MIRA3 TESCAN high resolution field emission scanning electron microscopy (FESEM). Magnetic properties of the all samples were investigated by a vibrating sample magnetometer (VSM, model MDK-VSM, Iran) with the maximum applied field of 20 kOe at room temperature. 3. Results and discussion 3.1. Thermal analysis It was observed that the dried gel combusted in a selfpropagating process and completely converted into brownish loose and fluffy powder after burning out. Thermal analysis was carried out to evaluate the mechanism for the formation of hexaferrite phase and to observe the effect of Mg and Ni addition on thermal behavior of the synthesized sample. Fig. 1 shows the differential thermal analysis (DTA) related to nitrate-citrate gels within the temperature range of 25e1200 C, and its characteristics are listed in Table 1. As can be seen in Fig. 1, during the heating of̊ as-prepared samples, various stages such as dehydration of water, decomposition of residual organic groups, and phase formation of hexagonal ferrites were observed. Endothermic peak, within the temperature range of 80e120 C was due to the emerged moisture and emission of water chemical bonds from the specimen [14]. The largest sharp exothermic peak at about 415 C was observed due to the oxidation-reduction reaction between metal nitrate and citric acid ions [24,15]. During the combustion reaction, citric acid ions acted as reluctant and nitrate ions were the oxidizing agent. As a result, nitrate ions not only provided a suitable condition for in-situ oxidization to decompose organic components, but also created a situation for citric acid to act as a fuel. Decomposition of organic components resulted in the large amount of H2O, CO2, and NO2 gases [25]. Relatively broader exothermic peak with the maximum at 520 C might be due to the decomposition of retained unreacted citric acid or nitrates after self-combustion process, but also the decomposition of metal carbonates formed during the reaction [12,26]. The endothermic peak at 640 C might be attributed to starting the transformation of hydroxide to oxide and formation of spinel nickel ferrite (NiFe2O4) and strontium mono ferrite (SrFe2O4) [27]. The exothermic one at 690 C could be due to cobalt spinel (CoFe2O4) formation [15]. Moreover, the exothermic peak observed at 700e750 C range might be attributed to starting the transformation from spinel ferrites structure and strontium mono ferrite
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3
Fig. 1. DTA measurements for the dried gels with different Mg and Ni content (x).
Table 1 DTA results of dried gel in temperature range of 24e1200 C in heating range of 10 C/min in atmosphere environment. Peak position ( C)
Modality
Characteristic
Ref
80e120 415 520 640 690 700e750 750e950
Endothermic Exothermic Exothermic Endothermic Exothermic Exothermic Fluctuant
Emerged moisture Combustion in citrate-nitrate reaction Decomposition of retained citric acid or nitrates Transformation of hydroxide to oxide Formation of cobalt spinel Formation of M-type hexagonal ferrite Formation of Y-type hexagonal ferrite
[14] [15,24] [12,26] [27] [15] [28,29] [30]
into M-type hexaferrite [28,29]. Fluctuating peaks within the temperature range of 750e950 C might indicate solid-state reactions between different spinel ferrites and M-type hexaferrite to the formation of single phase Y-type hexaferrite [30]. It can be also observed that, in the specimen with x ¼ 0.6, there were no exothermic and endothermic peaks after 800 C which indicated the beginning of the formation of Y-type hexaferrite phase. It demonstrated that, with increasing Mg contents, the temperature of Co2Y hexaferrite formation was decreased. To the best of our knowledge, it may be related to the increasing heat released in self-
propagation reaction, which suppresses the formation of a-Fe2O3 phase and is advantageous in terms of obtaining pure Co2Y hexaferrite phase at a relatively lower temperature [31]. 3.2. FT-IR studies The room temperature infrared spectra of Y-type hexaferrites are shown in Fig. 2. Spectra of the investigated samples measured in the frequency range of 4000e400 cm1 could be used to observe chemical and structural changes and presence of different crystal
100
% Transmittance
90 100
80 X = 0.0 X = 0.15 X = 0.3 X = 0.45 X = 0.6
70 60
80 60
50 40 4000
40
3600
3200
2800
2400
2000
650 600 550 500 450 400
1600
1200
800
400
Wave Numbers (Cm-1) Fig. 2. Infrared spectroscopy results of the calcined samples at 1000 C.
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Table 2 FT-IR spectroscopic data of sol-gel derived oxalate after calcinated at 1000 C for 3 h in air. Peak position (cm1)
Intensity
Vibrational mode(s)
Ref
3435 1633 1439 592 464
Strong Weak Weak Strong Medium
Surface hydroxyl group (eOH) Surface hydroxyl group (eOH) NeO stretching vibration of NO3 Oxygen and metal cations of octahedral site Oxygen and metal cations on tetrahedral sites
[9,26] [9,26] [33] [34,35] [34,35]
phases in the materials during calcination process. The spectra were quite similar for all the compositions and values of the absorption bands are summarized in Table 2. The results showed good agreement with the data reported in the literature [32]. The broad absorption band in 3435 cm1 and 1633 cm1 was the results of stretching and bending bands of the surface hydroxyl group (eOH) of magnetic particles acquired from wet atmosphere during calcination [9,26]. For the samples with x ¼ 0.0 and 0.15, the very low intensity absorption band at 1439 cm1 could be attributed to the anti-symmetric stretching vibration of NO 3 , indicating that nitrate ions are present in the calcined samples [33]. As seen in Fig. 2, with an increase of Mg due to enhancing self-propagation reaction heat in x > 0.15, vibration bands of nitrate functional group disappeared due to the decomposition of nitride ions. Absorption spectra of calcined samples showed two distinct peaks in low frequency region which were identified as the metal-oxygen stretching vibrations of hexaferrite [3]. The highest peaks in the range of 554e592 cm1 were attributed to the intrinsic vibration of octahedral sites, whereas the lowest peak observed at 433 cm1 showed the characteristic interaction between oxygen and metal cations of tetrahedral sites [34,35]. It was expected to see differences in the intensity of the bands in various compositions because of the difference in the amount of divalent cations in octahedral and tetrahedral sites. These two bands are the characteristics bands of all ferrites. As reported earlier [36], these bands are the evidence of the formation of the metal ions-oxygen bands in the hexagonal. The difference in the cation mass, cation-oxygen distance, and bonding forces could be responsible for the difference in the wavelength of bands for the calcined samples [36,37].
Fig. 3. XRD patterns of the samples calcined at 900 C for 3 h.
3.3. Phase identification Based on the results of DTA studies, the crystallization process of the dried gel of Y-type hexaferrite in the temperature range of
Fig. 4. XRD patterns of the samples calcined at 950 C for 3 h.
Fig. 5. XRD patterns of substituted Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1000 C for 3 h.
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5
900e1150 C was emphatically investigated. The X-ray diffraction of calcined specimens at 900 C for 3 h is shown in Fig. 3. This figure reveals that the powders calcined at this temperature contained strontium hexaferrite (JCPDS Card no. 00-024-1207) as the major and minor phases of hematite (JCPDS Card no. 01-073-0603), magnetite (JCPDS Card no. 00-003-0863), SrO (JCPDS Card no. 00001-0886), and spinel ferrites (JCPDS Card no. 00-001-1121, 00003-0875 and 01-071-1232). Also, the single phase Co2Y could not be obtained directly from the simple oxides due to the complexity of crystal structure and is usually produced from some intermediate phases formed at lower temperatures [16]. During the fabrication of Y-type hexaferrite, in fact, a set of chemical reactions has been done, which can be described by the following equations [30]:
Fig. 6. XRD patterns of substituted Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1150 C for 3 h.
gel þ g-Fe2O3 (burned gel as a precursor)
(1)
g-Fe2O3 þ SrO / SrFe2O4 (spinel ferrite)
(2)
SrFe2O4 þ 5g-Fe2O3 / SrFe12O19 (M-type hexaferrite)
(3)
SrFe12O19 þ 6g-Fe2O3 þ 3SrO þ 4CoO / 2Sr2Co2Fe12O22 (Y-type hexaferrite) (4) Based on the above equations, the citrate-nitride gels presented
Fig. 7. FESEM micrographs of the samples calcined at 950 C: (a) x ¼ 0.0, (b) x ¼ 0.3, (c) x ¼ 0.6.
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self-propagation combustion behavior and none of them could be converted directly into the Y-type hexagonal crystal phase during combustion. When the samples were heated at 450 C, the gel was transformed into the intermediate phase g-Fe2O3, which had a cubic spinel structure with chemical formula Fe6O2þ 8 (similar to S block in M-type and Y-type hexaferrite) via dehydration and decomposition. g-Fe2O3 reacted easily with SrO to form SrFe2O4 and then further reacted with SrFe2O4 to form SrFe12O19 at lower temperature. With increasing the calcination temperature, SrFe12O19 reacted with g-Fe2O3, CoO, and SrO to form single-phase Sr2Co2Fe12O22. Indeed, Reaction (4) indicates that, with the improvement of calcination temperature, strontium hexaferrite, spinel ferrite, and SrO reacted together and were gradually transformed into Co2Y. In comparison with the standard Y-type hexaferrite (JCPDS Card no. 01-082-0472), it can be seen that, in the samples calcined at 950 C for x ¼ 0.0 and 0.3 (Fig. 4), the powders consisted of Y-type hexaferrites along with the presence of a small amount of secondary phases such as hematite, SrO, and CoFe2O4. Also, with increasing the Mg and Ni contents at x ¼ 0.6, the peaks corresponding to impurity phases apparently disappeared. It means that increasing Mg content decreased the phase formation temperature of Y-type hexaferrite. When calcination temperature was raised to 1000 C (Fig. 5), it can be seen that all of the diffraction patterns matched strongly with the standard patterns of JCPDS Card no. 01-082-0472 and no
unreacted components were present in the final product. Crystallite size of all the calcined samples was calculated using Scherrer's equation and found to be 45e63 nm. Even though the calcination temperature was reached up to 1100 C, no diffraction patterns change was observed. Similar results have been demonstrated in such works on Y-type hexaferrites [34,38]. Furthermore, at 1150 C (Fig. 6), single phase Co2Y starts to decompose into the previous intermediate phases again. 3.4. Morphology and grain size Microstructures of all the calcined specimens at different temperature were studied using field emission scanning electron microscopy (FESEM). Figs. 7e9 display the representative FESEM micrographs of Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite (where x ¼ 0.0, 0.3, and 0.6) calcined at temperatures between 950 and 1050 C for 3 h in the air atmosphere. As can be seen in Fig. 7 (a, b, and c), the amount of the intermediate phases such as spinel ferrites, SrO, and M-type hexaferrite identified by XRD analysis decreased as MgNi contents increased, while the major phase (Y-type hexaferrite) with hexagonal plate like morphology increased. After the substitution of divalent cations at x ¼ 0.6, the intermediate phases completely disappeared and only hexagonal-shaped Co2Y was obtained. The reduction of intermediate phases at higher x values can be attributed to the
Fig. 8. FESEM micrographs of the Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1000 C: (a) x ¼ 0.0, (b) x ¼ 0.3, (c) x ¼ 0.6.
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effect of dopants, particularly Mg2þ ions, on the heat of autocombustion reaction. This result was in good agreement with DTA data, in which after 800 C, with increasing Mg2þ contents, this curve became smooth and no endothermic and exothermic peaks
7
were observed at x ¼ 0.6, which can be interpreted as decreasing the formation temperature of Y-type hexaferrite. As shown in Fig. 8 (a, b, and c), when temperature increased to 1000 C, due to the reaction of retained M-type hexaferrite with other intermediate
Fig. 9. FESEM micrographs of the Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite samples calcined at 1050 C: (a) x ¼ 0.0, (b) x ¼ 0.3, (c) x ¼ 0.6.
Fig. 10. FESEM micrographs of the Sr2Co2xMgx/2Nix/2Fe12O22 (x ¼ 0.3) hexaferrite samples calcined at 1150 C.
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phases, the single phase of Y-type hexaferrite was obtained in all the samples [34]. It can be considered that the Y-type hexaferrites at 1000 C showed well defined hexagonal platelet like shapes with an almost uniform particle size distribution. Moreover, the thickness of the particle as calculated using Image J software was smaller for the ferrites substituted with higher values of Ni2þ and Mg2þ ions (40 nm) than those of pure hexaferrite (110 nm). Shape of the grains is very important for specific applications in different fields and it has been reported that the platelet-shaped hexaferrite can be used as microwave absorbing coatings [2]. Mean size of the particles increased with the increase of calcination temperature. As temperature increased to 1050 C (Fig. 9aec), thickness of the hexagonal flakes for x ¼ 0.0, 0.3, and 0.6 increased to about 257, 248, and 231 nm, respectively. Further, particle growth and neck formation were due to the promotion of diffusion mechanisms at higher temperatures. It could be also observed that, with the further increase of temperature to 1150 C (Fig. 10), some impurities were seen on the surface of hexagonal flakes, probably due to the decomposition of Co2Y particles into some previous intermediate phases like Fe3O4 and SrFe12O19 confirmed by EDS analysis (Fig. 11). In addition, it has been reported that, with increasing the calcination temperature, the tendency of the particles for joining together is enhanced and large particles (2.3 mm) with hexagonal pyramidal shape are generated [27,39]. 3.5. Magnetic properties The magnetic hysteresis loops for Y-type hexaferrites calcined at temperatures from 950 C to 1150 C are shown in Figs. 12 and 13. Magnetic properties such as coercivity (Hc), saturation magnetization (Ms), remanence (Mr), and squareness ratio (Mr/Ms) were measured at 20 kOe and summarized in Table 3. Width of the loops showed that all of the samples had small coercivity and were relatively soft hexaferrites. Fig. 12 demonstrates the hysteresis loops of the samples with x ¼ 0.3 calcined at 950 to 1150 C. Values of saturation magnetization (Ms), remanence (Mr), and coercivity for all the samples were found to be in the range of (30.00e56.12) emu/g, (10.62e22.98) emu/g, and (250e1140) Oe, respectively. They were very close to typical values reported for nanostructured Y-type hexaferrites [40]. It is clear that, with the increase in the calcination temperature from 950 to 1000 C, Ms and Mr were increased significantly (due to the removing of intermediate phases) and remained constant with further increase of temperature to 1100 C and then decreased at 1150 C. The latter reduction of the magnetization values can be the result of hexaferrite decomposition at higher temperatures as confirmed by XRD patterns. Also, values of coercivity decreased continuously from 1140 to 250 Oe with increasing the calcination temperature from 900 to 1150 C. It is well known that the size of particles has a significant effect on the coercivity of hexaferrite. This typical behavior is attributable to the transition from single to multi domain structures, which occurs with increasing grain size at higher temperatures [41]. Critical size of a single domain particle for Y-type hexaferrite is reported to about 1.18 mm [34,42,43]. When the particle size becomes bigger than the critical value, most of them would exist in a multi domain state. As shown in FESEM micrographs (Figs. 7e10), with an increase in the calcination temperature, the particle size also increased significantly. As the particles became larger than the single domain size, value of coercivity decreased noticeably to 250 Oe. Similar results have been also observed in the recent studies for strontium and barium hexaferrites [44,45]. On the basis of these results, it is obvious that, in our case, the coercivity of hexaferrites can be controlled greatly by calcinating temperature and thus by grain size. It is known that hexaferrites which have low coercivity are useful for security,
Fig. 11. EDS spectrum of the calcined samples at 1150 (b) SrFe12O19, (c) Fe3O4.
C:
(a) Sr2Co2xMgx/2Nix/
2Fe12O22,
switching, microwave devices, and especially high frequency applications [12]. Fig. 13 shows the hysteresis loops of the samples with x ¼ 0.0 and 0.6 calcined at 950 C, where the values of saturation magnetization were found to be 30 and 51 emu/g, respectively. Magnetic behavior of these samples can be described according to the effect of magnesium contents on the formation of Y-type hexaferrite from intermediate phases (as discussed in Section 3.3). The results showed that the saturation magnetization of undoped hexaferrite (x ¼ 0.0) a much less than the values reported in
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9
60 24
45
20 16 12
15 0 -15
)
Magnetization (emu/g)
30
(a) (b) (c) (d) (e)
)
-30 -45 400
-60 -20000 -16000 -12000
-8000
-4000
0
4000
8000
800
1200
12000
16000
20000
Applied Field (Oe) Fig. 12. Magnetic hysteresis loops of Sr2Co2xMgx/2Nix/2Fe12O22 (x ¼ 0.3) hexaferrite samples calcined at (a) 950 C, (b) 1000 C, (c) 1050 C, (d) 1100 C, (e) 1150 C.
60 24
45 18 12
)
Magnetization (emu/g)
30 15 0
(a) (b)
)
-15 -30 -45
1100 1200 1300
-60 -20000 -16000 -12000
-8000
-4000
0
4000
8000
12000
16000
20000
Applied Field (Oe) Fig. 13. Magnetic hysteresis loops of calcined samples at 950 C for (a) x ¼ 0.0 and (b) x ¼ 0.6.
recent studies (about 59 emu/g) [45]. As confirmed from XRD pattern of un-substituted specimen in Fig. 4a, it can be due to the dilution of the strontium hexaferrite by the secondary phase (hematite) which is a weak ferromagnetic material at room temperature with Ms~ 0.8 emu/g at 18 kOe [46e49]. Also, the effects of SrO can be neglected, as it is diamagnetic. In addition, Fig. 13b shows that the saturation magnetization increased to 51.25 emu/g with increasing Mg content (x ¼ 0.6). Again, it could be attributed to the influence of Mg addition on the formation of Y-type hexaferrite and removing the intermediate phases. Also, Fig. 13a demonstrates that the coercivity of undoped hexaferrite (x ¼ 0.0) was much less than the values reported for pure strontium hexaferrite (about 5000 Oe)
[45,32]. High coercivity of pure strontium hexaferrite was due to strong uniaxial anisotropy along the c-axis of M-type hexaferrite. But, doping of Co, Ni, and especially Mg in strontium hexaferrite led to a rapid decrease in coercivity. The result could be attributed to the reduction in the crystal anisotropy field due to the change of the easy-axis of magnetization from the c-axis to the basal plane [50]. 4. Conclusion 1 Nano-crystalline and single phase Mg-Ni doped Sr2Co2xMgx/ 2Nix/2Fe12O22 (Co2Y) hexaferrites (space group R3/m) with the average crystallite size in the range of 45e63 nm were
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Table 3 Effects of calcination temperature on saturation magnetization (Ms), remanence magnetization (Mr), squareness and coercivity (Hc) of Sr2Co2xMgx/2Nix/2Fe12O22 hexaferrite (x ¼ 0.3 and 0.6). Sample (x)
Temperature ( C)
Ms (emu/g)
Mr (emu/g)
Squareness
Hc (Oe)
0.3 0.6 0.3 0.3 0.3 0.3
950 950 1000 1050 1100 1150
30.00 51.25 56.12 56.00 55.53 50.06
13.30 22.01 22.98 22.46 19.11 10.62
0.44 0.43 0.41 0.40 0.34 0.21
1140 1230 950 900 634 250
successfully synthesized via the auto-combustion sol-gel technique followed by calcinations at temperatures between 950 and 1100 C. 2 The X-ray diffraction patterns revealed the formation of single phase Y-type hexaferrite at temperature of 950 C for the sample with x ¼ 0.6, while additional impurity phases such as a-Fe2O3 and SrO were observed in the samples with x ¼ 0.0 and 0.3. 3 From FESEM micrographs, it can be concluded that hexaferrite particles with well-defined platelet hexagonal shapes were synthesized and the thickness of the particles was decreased with increasing Mg2þ content. 4 Magnetization measurements demonstrated that the presence of SrO and weak ferromagnetic a-Fe2O3 beside Co2Y hexaferrite in the final product reduced the magnetization from 56 to 30 emu/g. The saturation magnetization values did not show any considerable changes, whereas coercivity was strongly decreased from 950 to 250 Oe by increasing the calcination temperatures. Based on above characteristics, it can be concluded that the synthesized hexaferrites can be promising candidates for very high frequency applications ranged from 900 MHz to 3 GHz. Acknowledgment The authors would like to thank the Iranian Nanotechnology Initiative Council (Grant no. 45519) for providing us with financial support in this project. References [1] G.H. Jonker, H.P.J. Wijn, P.B. Braum, Magnetic and microwave absorbing properties of m-type hexaferrites substituted by Ru-Co (BaFe122xRuxCoxO19), Philips Tech. Rev. 18 (1956) 145. [2] R.C. Pullar, Hexagonal ferrites: a review of the synthesis, properties and applications of hexaferrite ceramics, Prog. Mater. Sci. 57 (2012) 1191e1334. [3] G. Murtaza, R. Ahmad, T. Hussain, R. Ayub, I. Ali, M.A. Khan, M.N. Akhtar, Structural and magnetic properties of NdeMn substituted Y-type hexaferrites synthesized by microemulsion method, J. Alloy. Compd. 602 (2014) 122e129. [4] J. Kulikowski, Magnetostrictive properties of Cox(NiZn)1xFe2O4 ferrites in the case of small changes of iron content, J. Magn. Magn. Mater. 41 (1984) 56. [5] M. Irfana, M.U. Islam, I. Ali, M.A. Iqbal, N. Karamat, H.M. Khan, Effect of Y2O3 doping on the electrical transport properties of Sr2MnNiFe12O22 Y-type hexaferrite, Curr. Appl. Phys. 14 (2014) 112e117. [6] J.T. Lim, C.M. Kim, B.W. Lee, C.S. Kim, Investigation of magnetic properties of non-magnetic ion (Al, Ga, In) doped Ba2Mg0.5Co1.5Fe12O22, J. Appl. Phys. 111 (2012), 07A518. [7] A.M. Abo El Ata, S.M. Attia, Dielectric dispersion of Y-type hexaferrites at low frequencies, J. Magn. Magn. Mater. 257 (2003) 165e174. [8] Y. Bai, J. Zhou, Z. Gui, L. Li, Phase formation process, microstructure and magnetic properties of Y-type hexagonal ferrite prepared by citrate solegel auto-combustion method, Mater. Chem. Phys. 98 (2006) 66e70. [9] A. Elahi, M. Ahmad, I. Ali, M.U. Rana, Preparation and properties of solegel synthesized Mg-substituted Ni2Y hexaferrites, J. Ceram. Int. 39 (2013) 983e990. [10] I. Ali, M.U. Islam, M.N. Ashiq, M.A. Iqbal, H.M. Khan, N. Karamat, Effect of TbeMn substitution on DC and AC conductivity of Y-type hexagonal ferrite, J. Alloy. Compd. 579 (2013) 576e582. es, [11] G.F.M. Pires Júniora, H.O. Rodrigues, J.S. Almeida, E.O. Sancho, J.C. Go M.M. Costa, J.C. Denardin, A.S.B. Sombra, Study of the dielectric and magnetic properties of Co2Y, Y-type hexaferrite (Ba2Co2Fe12O22) added with PbO and Bi2O3in the RF frequency range, J. Alloy. Compd. 493 (2010) 326e334.
[12] M. Ahmad, Q. Ali, I. Ali, I. Ahmad, M.A. Khan, M.N. Akhtar, G. Murtaza, M.U. Rana, Effects of Sr-substitution on the structural and magnetic behavior of Ba-based Y-type hexagonal ferrites, J. Alloy. Compd. 580 (2013) 23e28. [13] M.J. Iqbal, F. Liaqat, Physical and electrical properties of nanosized Mn- and Cr-Doped strontium Y-Type hexagonal ferrites, J. Am. Ceram. Soc. 93 (2010) 474e480. [14] M.J. Iqbal, M.N. Ashiq, P.H. Gomez, J.M. Munoz, Influence of annealing temperature and doping rate on the magnetic properties of ZreMn substituted Srhexaferrite nanoparticles, J. Alloy. Compd. 500 (2010) 113e116. [15] M.M. Rashad, M. Rasly, H.M. El-Sayed, A.A. Sattar, I.A. Ibrahim, Controlling the composition and the magnetic properties of hexagonal Co2Z ferrite powders synthesized using two different methods, J. Appl. Phys. A 112 (2012) 963e973. [16] Y. Bai, J. Zhou, Z. Gui, L. Li, An investigation of the magnetic properties of Co2Y hexaferrite, J. Mater. Lett. 57 (2002) 807e811. [17] I. Ali, M.U. Islam, M.N. Ashiq, M.A. Iqbal, H.M. Khan, G. Murtaza, Role of grain boundaries in the conduction of EueNi substituted Y-type hexaferrites, J. Magn. Magn. Mater. 362 (2014) 115e121. [18] H.I. Hsiang, R.Q. Yao, Synthesis of 3BaO.2CoO.12Fe2O3 powder using chemical co-precipitation, J. Magn. Magn. Mater. 307 (2006) 273e278. [19] M. Rasly, M.M. Rashad, Structural and magnetic properties of SneZn doped BaCo2Z-type hexaferrite powders prepared by citrate precursor method, J. Magn. Magn. Mater. 338 (2013) 58e64. gard, K. Bobzin, G. Bolelli, A. Hujanen, P. Lintunen, D. Lisjak, S. Gyergyek, [20] M. Be €fer, T. Varis, Thermal spraying of L. Lusvarghi, M. Pasquale, K. Richardt, T. Schla Co,Ti-substituted Ba-hexaferrite coatings for electromagnetic wave absorption applications, Surf. Coat. Technol. 203 (2009) 3312e3319. [21] M. Ahmada, R. Grossinger, M. Kriegisch, F. Kubel, M.U. Rana, Characterization of Sr-substituted W-type hexagonal ferrites synthesized by solegel autocombustion method, J. Magn. Magn. Mater. 332 (2013) 137e145. [22] V.N. Dhage, M.L. Mane, A.P. Keche, C.T. Birajdar, K.M. Jadhav, Structural and magnetic behaviour of aluminium doped barium hexaferrite nano particles synthesized by solution combustion technique, Phys. B Condens. Matter 406 (2011) 789. [23] M.C. Dimri, A. Verma, S.C. Kashyap, D.C. Dube, O.P. Thakur, C. Prakash, Structural, dielectric and magnetic properties of NiCuZn ferrite grown by citrate precursor method, J. Mater. Sci. Eng. B 133 (2006) 42. [24] M.M. Rashad, M. Rasly, H.M. El-Sayed, A.A. Sattar, I.A. Ibrahim, Controlling the composition and the magnetic properties of hexagonal Co2Z ferrite powders synthesized using two different methods, Appl. Phys. A 112 (2013) 963e973. [25] A. Mali, A. Ataie, Influence of the metal nitrates to citric acid molar ratio on the combustion process and phase constitution of barium hexaferrite particles prepared by solegel combustion method, Ceram. Int. 30 (2004) 1979. €ssinger, M. Kriegisch, F. Kubel, M.U. Rana, Magnetic and [26] M. Ahmada, R. Gro microwave attenuation behavior of Al-substituted Co2W hexaferrites synthesized by sol-gel autocombustion process, Curr. Appl. Phys. 12 (2012) 1413e1420. [27] S. Tyagi, H.B. Baskey, R.C. Agarwala, V. Agarwala, Development of hard/soft ferrite nanocomposite for enhanced microwave absorption, J. Ceram. Int. 37 (2011) 2631e2641. [28] H.I. Hsiang, R.Q. Yao, Formation mechanism of 3BaO$2CoO$12Fe2O3 powder synthesized using chemical co-precipitation, J. Alloy. Compd. 453 (2008) 366e370. [29] H.I. Hsiang, R.Q. Yao, Hexagonal ferrite powder synthesis using chemical coprecipitation, Mater. Chem. Phys. 104 (2007) 1e4. [30] X.F. Yang, Q. Jin, Z.P. Chen, Q.L. Li, B. Liu, Fabrication and microwave absorbent properties of Cobate zinc substituted W-type BaCoZnFe16O27, J. Magn. Magn. Mater. 367 (2014) 64e68. [31] C.J. Li, B. Wang, J.N. Wang, Magnetic and microwave absorbing properties of electrospun Ba(1x)LaxFe12O19Nanofibers, J. Magn. Magn. Mater. 324 (2012) 1305e1311. [32] S.K. Chawla, R.K. Mudsainiyan, S.S. Meena, S.M. Yusuf, Solegel synthesis, structural and magnetic properties of nanoscale M-type barium hexaferrites BaCoxZrxFe(122x)O19, J. Magn. Magn. Mater. 350 (2014) 23e29. [33] A. Ghasemi, Development of uniaxial magnetocrystalline anisotropy in SrFe12x(DyGd)xO19 thin film synthesized by incorporation of high coercivity nanoparticles in solegel method, J. Magn. Magn. Mater. 361 (2014) 112e117. [34] C. Zhang, J. Shi, X. Yang, L. De, X. Wang, Effects of calcination temperature and solution pH value on the structural and magnetic properties of Ba2Co2Fe12O22 ferrite via EDTA-complexing process, J. Mater. Chem. Phys. 123 (2010)
Please cite this article in press as: Y. Alizad Farzin, et al., Synthesis behavior and magnetic properties of Mg-Ni co-doped Y-type hexaferrite prepared by sol-gel auto-combustion method, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.04.082
Y. Alizad Farzin et al. / Materials Chemistry and Physics xxx (2016) 1e11 551e556. [35] A. Aslama, M.U. Islama, I. Alia, M.S. Awanb, M. Irfana, A. Iftikhar, High frequency electrical transport properties of CoFe2O4 and Sr2NiMnFe12O22 composite ferrites, J. Ceram. Int. 40 (2014) 155e162. € ssinger, M. Kriegisch, F. Kubel, M.U. Rana, Effects of [36] M. Ahmada, I. Ali, R. Gro divalent ions substitution on the microstructure, magnetic and electromagnetic parameters of Co2W hexagonal ferrites synthesized by solegel method, J. Alloy. Compd. 579 (2013) 57e64. [37] M.J. Iqbal, B. Ain, Synthesis and study of physical properties of Zr4þeCo2þ codoped barium hexagonal ferrites, Mater. Sci. Eng. B 164 (2009) 6e11. [38] Y. Alizad Farzin, O. Mirzaee, A. Ghasemi, Influence of Mg and Ni substitution on structural, microstructural and magnetic properties of Sr2Co2xMgx/2Nix/ 2Fe12O22 (Co2Y) hexaferrite, J. Magn. Magn. Mater. 371 (2014) 14e19. [39] Z. Mosleh, P. Kameli, M. Ranjbar, H. Salamati, Effect of annealing temperature on structural and magnetic properties of BaFe12O19 hexaferrite nanoparticles, Ceram. Int. 40 (2014) 7279e7284. [40] J. Jalli, Y.K. Hong, S. Bae, J.J. Lee, G.S. Abo, J.H. Park, B.C. Choi, T. Mewes, S.G. Kim, S.H. Gee, I.T. Nam, T. Tanaka, Magnetic and microwave properties of ferromagnetic Zr-substituted Ba2Zn2Fe12O22 (Zn-Y) single crystals, J. Appl. Phys. 109 (2011), 07A509. € zeri, Z. Durmus, A. Baykal, E. Uysal, Preparation of high quality, single [41] H. So domain BaFe12O19 particles by the citrate solegel combustion route with an initial Fe/Ba molar ratio of 4, Mater. Sci. Eng. B 177 (2012) 949e955. [42] C. Sudakar, G.N. Subbanna, T.R.N. Kutty, Wet chemical synthesis of multicomponent hexaferrites by gel to crystallite conversion and their magnetic properties, J. Magn. Magn. Mater. 263 (2003) 253e268.
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[43] Z.F. Zi, Y.P. Sun, X.B. Zhu, Z.R. Yang, J.M. dai, W.H. Song, Structural and magnetic properties of SrFe12O19 hexaferrite synthesized by a modified chemical coprecipitation method, J. Magn. Magn. Mater. 320 (2008) 2746e2751. [44] M. Ahmad, I. Ali, F. Aen, M.U. Islam, M.N. Ashiq, S. Atiq, W. Ahmad, M.U. Rana, Effect of sintering temperature on magnetic and electrical properties of nanosized Co2W hexaferrites, Ceram. Int. 38 (2012) 1267e1273. [45] H. Luo, B.K. Rai, S.R. Mishra, V.V. Nguyen, J.P. Liu, Physical and magnetic properties of highly aluminum doped strontium ferrite nanoparticles prepared by auto-combustion route, J. Magn. Magn. Mater. 324 (2012) 2602e2608. [46] H. Ashima, S. Sanghi, A. Agarwal, D. Reetu, Rietveld refinement, electrical properties and magnetic characteristics of CaeSr substituted barium hexaferrites, J. Alloy. Compd. 513 (2012) 436e444. [47] T. Tsutaoka, N. Koga, Magnetic phase transitions in substituted barium ferrites BaFe12x(Ti0.5Co0.5)xO19 (x ¼ 0e5), J. Magn. Magn. Mater. 325 (2013) 36e41. nchez-De Jesús, A.M. Bolarín-Miro , C.A. Corte s-Escobedo, R. Valenzuela, [48] F. Sa S. Ammar, Mechanosynthesis, crystal structure and magnetic characterization of M-type SrFe12O19, Ceram. Int. 40 (2014) 4033e4038. [49] M. Tadic, N. Citakovic, M. Panjan, B. Stanojevic, D. Markovic, D. Jovanovic, V. Spasojevic, Synthesis, morphology and microstructure of pomegranate-like hematite (a-Fe2O3) superstructure with high coercivity, J. Alloy. Compd. 543 (5) (2012) 118e124. [50] A. Sharbati, J. Molaverdi Khani, G.R. Amiri, Microwave absorption studies of nanocrystalline SrMnx/2(TiSn)x/4Fe12xO19 prepared by the citrate solegel method, Solid State Commun. 152 (2012) 199e203.
Please cite this article in press as: Y. Alizad Farzin, et al., Synthesis behavior and magnetic properties of Mg-Ni co-doped Y-type hexaferrite prepared by sol-gel auto-combustion method, Materials Chemistry and Physics (2016), http://dx.doi.org/10.1016/j.matchemphys.2016.04.082