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Structural and magnetic studies of Ti4+substituted M-type BaFe12O19 hexa-nanoferrites
Materials Science in Semiconductor Processing 40 (2015) 374–382
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Structural and magnetic studies of Ti4 þ substituted M-type BaFe12O19 hexa-nanoferrites M.A. Amer a,n, T.M. Meaz a, S.S. Attalah b, A.I. Ghoneim a a b
Physics Department, Faculty of Science, Tanta University, 31527 Tanta, Egypt Reactor and Neutron Physics Department, Nuclear Research Center, Cairo, Egypt
art ic l e i nf o
a b s t r a c t
Article history: Received 19 April 2015 Received in revised form 5 July 2015 Accepted 6 July 2015
M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles, 0 r x r1, were prepared by the chemical co-precipitation method. XRD, TEM, FT-IR, TGA, DTA and VSM techniques were used to characterize the samples. This study proved the formation of single-phase M-type hexagonal nanoferrites. The average particle and crystallite (R) sizes, lattice parameter c, experimental and theoretical densities, strain (ε), saturation magnetization (Ms), magnetic moment showed decrease against x, whereas the lattice constant a, porosity (P) and specific surface area showed increase. The force constants and trend of band positions and Debye temperature were x dependent, whereas the coercivity, remanent magnetization, squareness and anisotropy constant did not. The net weight loss of the samples led in the range of 0.00418–0.01834% weight where the maximum weight loss occurred before heating at 500 °C. P and R showed strong effect on Ms and ε. & 2015 Elsevier Ltd. All rights reserved.
Keywords: BaTixFe12 (4/3)xO19 nanoparticles Structural and magnetic properties Thermal analysis
1. Introduction Recently, advanced researches have greatly devoted to develop new nanomaterials for applications in the fields of shielding technology, recording material due to their large magneto-crystalline anisotropy, relatively high saturation magnetization, nontoxicity, excellent chemical stability and good corrosion resistivity [1,2]. The fine particle size, high specific surface area, high and hard magnetization and chemical homogeneity of nanoparticles are required for important technological applications. In addition, hexagonal nanoferrites are candidate materials as a radar absorbing material due to their high permeability, magnetization and other good dielectric properties. Furthermore, hexagonal ferrites are hard-magnetic magnets with high saturation magnetization and maximum coercivity which make them highly recommended for such applications. M-type hexagonal nanoferrites have been investigated intensively due to their fine particle size, high specific surface area and good chemical and thermal stability. Their magnetoplumbite structure of general formula MFe12O19 (M ¼ Ba, Sr) is an appropriate candidate for several applications such as permanent magnet and recording media [2]. Many researchers prepared M-type hexagonal nanoferrites with different substituted ions using different preparation n
Corresponding author. Fax: þ20 403350804. E-mail addresses: [email protected], [email protected] (M.A. Amer). http://dx.doi.org/10.1016/j.mssp.2015.07.007 1369-8001/& 2015 Elsevier Ltd. All rights reserved.
methods and characterized the obtained samples by different techniques [3–6]. The crystallite and grain sizes, structural and lattice parameters, saturation magnetization, coercivity, magneton number, microstrain and dislocation density of the nanoferrites were affected by the preparation conditions, thermal treatments and substitution process. The obtained results were discussed depending on accumulated data and comparing with the bulk materials. This investigation is devoted to synthesize M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles by the chemical co-precipitation method. The samples were characterized using X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermo gravimetric and differential thermal analysis and vibrating sample magnetometry.
2. Experimental 2.1. Sample preparation M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles, x¼ 0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1 were prepared by the chemical co-precipitation method according to the equation [7]; Ba(NO3)2 þxTi(C12H28O4)þ (12–(4)/(3)x)Fe(NO3)3 9H2Oþ (38 4x) NaOH-BaTixFe12 (4/3)xO19 þ(38 4x)NaNO3 þ4x(CH3)2CHOHþ (127 16x)H2O
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Fig. 5. Variation of the specific surface area S and strain ε against x.
Fig. 1. XRD patterns of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites.
Fig. 2. Dependence of the lattice constants a and c on Ti4 þ ion content x.
Fig. 6. Dependence of strain ε on the crystallite size R and porosity P.
Fig. 3. Variation of the crystallite size R against x.
Fig. 4. Variation of the density D, theoretical density Dx, and porosity P with x.
Stoichiometric proportion amounts of the high purity Ba(NO3)2, Ti(C12H28O4) and Fe(NO3)3 9H2O were dissolved in distilled water and kept in about 10 °C for one hour (h). The reactants were mixed
and constantly stirred using a magnetic stirrer for 10 min. The NaOH solution was added drop wise where the pH of mixed solution was constantly monitored as pH E13. Then the solution was heated and maintained at 90 °C for 2 h under continuous stirring till the precipitation occurred. The precipitates were thoroughly washed with distilled water until the washings become free from sodium chloride. The precipitates were dried for a few days at room temperature. Then the samples were thoroughly ground in an agate mortar to obtain fine powder. Thereafter, the samples were annealed for 20 h at 1200 °C and then slowly cooled to room temperature. The samples were ground to fine powder and annealed again at 1200 °C for 20 h and then slowly cooled to room temperature. Finally, the nanoparticle samples were ground to fine powder. 2.2. Measurements The nanoparticle samples were characterized by X-ray diffraction using GNR APD 2000 Pro X-ray diffractometer step scan type and CuKα1 radiation at wavelength λ ¼1.540598 Å. The lattice
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Fig. 7. TEM images for the BaTixFe12 4/3xO19 nanoferrites.
Table 1 The average particle size (Z) of BaTixFe12 4/3xO19 nanoferrites; error¼ 7 0.2. x Z (nm)
0.0 61.3
0.125 60.5
0.25 56.6
0.375 52
0.5 50
0.75 42.4
1 46.3
constants a and c were calculated using the relations [8]:
1 4 ⎛ h2 + hk + k 2 ⎞ l2 ⎟+ 2 = ⎜ 2 2 3⎝ dhkl a ⎠ c ⎡ ⎛ A1B − AB1 ⎢4 a=⎢ ⎜ 3 ⎜⎝ B/d12 − B1/d2 ⎣
(
⎡ A B − AB ⎤1/2 1 ⎥ c=⎢ 12 ⎣ A1/d − A/d12 ⎦
)
1/2 ⎞⎤ ⎟⎥ ⎟⎥ ⎠⎦
Fig. 8. IR absorption spectra of the M-type hexagonal BaTixFe12 (4/3)xO19 nanoferrites.
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Table 2 IR absorption band positions νn, n¼ 1, 2,… and T, and force constants F1 and F2, error¼ 7 0.02. x 0 0.125 0.25 0.375 0.5 0.75 1
ν1 (cm 1)
ν2 (cm 1)
ν3 (cm 1)
ν4 (cm 1)
νA (cm 1)
νB (cm 1)
F1n105 (dyne/cm)
F2n105 (dyne/cm)
582.50 584.42 584.58 580.56 584.43 582.49 586.35
435.90 433.97 437.83 435.95 439.76 437.78 435.98
335.60 333.68 335.63 335.65 335.69 337.57 337.40
231.50 237.20 237.21 237.22 237.23 237.24 237.25
885.30 896.87 871.80 869.85 889.16 883.38 877.59
1022.25 1016.50 1006.82 1001.03 1004.89 1010.67 1020.32
2.49 2.5 2.5 2.47 2.5 2.48 2.52
1.39 1.38 1.4 1.39 1.42 1.4 1.4
Fig. 9. Dependence of Debye temperature �D and threshold frequency νth on x.
where d is the interplaner distance, A¼ h2 þhþ k2; B ¼l2 and A1 = h12 + h1k1 + k12 ; B1=l12 . The crystallite size R was determined using the prominent diffraction peak (107) and Scherrer’s formula [8]:
R=
0.9λ β1/2 cos θ
where K ¼0.9 and β1/2 is the full width at half maximum of the peak (107). The porosity (P) of the samples was calculated using the equation [9]:
P=1−
D Dx
The obtained values of lattice constant a lie in the range of 5.8782–5.902 Å and c in the range of 23.1061–23.1636 Å where c/ aE 3.921 which agree with the published data [3,12]. The values of a and c are plotted against x as seen in Fig. 2. It is seen that c decreases with x, whereas a increases which can attribute to the substitution of the larger ionic radius Fe3 þ ions (0.64 Å) by Ti4 þ ions (0.61 Å) [3,12]. The determined crystallite size R values lie in the range of 41.4– 59.1 nm as illustrated in Fig. 3. It is illustrated that R decreases with x which may ascribe to the substitution process and improving the crystallization process [13,14]. Variation of the sample experimental density D, theoretical density (X-ray density) Dx and porosity P against x is displayed in Fig. 4. It is displayed that Dx and D decrease with x, whereas P increases. The decrease of Dx and D is attributed to the substitution of larger atomic weight Fe3 þ ions (55.85) by Ti4 þ ions (47.9). The increase in P with x may point to increase in oxygen vacancies which play a predominant role in densification and packing of the samples and may assign to that D decreases more than Dx [9,15]. The specific surface area (S) and strain (ε) were calculated using the equations [12,13]:
β1/2 cos θ = S=
0.9λ + 4ε sin θ R
6000 RDx
where D and Dx are the experimental and theoretical (X-ray) densities, respectively. The average nanoparticle size was determined by using JEOL JEM–100 SX transmission electron microscope. Infrared absorption spectra of the samples were recorded in the range of 200– 2000 cm 1 using a Bruker Tensor 27 FT-IR spectrometer. Simultaneous thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) of the nanoferrite samples were carried out in N2-atmosphere using an Perkin-Elmer STA 6000 thermal analysis system at heating rate of 15 °C/min. Hysteresis loops of the samples were recorded at room temperature using the vibrating sample magnetometer (LDJ) Electronic Inc. Troy, MI and a maximum applied field up to 25,000 Gauss.
The graph of β1/2 cos θ against 4sin θ shows a straight line whose slope gives the value of ε. Fig. 5 illustrates variation of S and ε with x. It is illustrated that S increases with x, whereas ε decreases. The increase of S is attributed to decrease in R and D. When the nanoparticle has smaller crystallite size that means it has a larger specific surface area [12]. The decrease of ε may be assigned to decreasing R where the negative strain values prove compressive strain [12–14,16]. The decrease of strain indicates the mechanical properties of samples such as the stability of nanostructure, adhesion between and/or within the nanoparticles and grain hardness. The decrease of ε enhances the decreases of R and increase of S where they prove the decrease of lattice volume [12– 14,16]. The dependence of ε on R and P is clear in Fig. 6 which indicates that ε increases against R and decreases against P.
3. Results and discussion
3.2. Transmission electron microscope (TEM) images
3.1. X-ray diffraction (XRD) analysis
TEM images of BaTixFe12 4/3xO19 nanoferrites are depicted in Fig. 7. It is depicted that the nanoparticles are agglomerated to each other where the nanoparticles for x Z0.75 are something granular. The agglomeration occurs and increases at higher annealing temperature which causes increase of the interaction between magnetic particles [17,18]. The obtained average values of nanoparticle size (Z) are listed in Table 1. Table 1 presents that the Z values are a little higher compared
Fig. 1 shows the XRD patterns of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites, x¼ 0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1. It is shown that the reflection planes (110), (107), (114), (203), (205), (217), (2011) and (220) appear in all the spectra which proves that the samples have a single-phase M-type hexagonal structure [10,11], as compared with JCPDS data (Card nos. 00-027-1029, 00-007-0276 and 01-079-1411).
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Fig. 10. TGA curves for M-type hexagonal BaTixFe12 4/3xO19 nano-ferrites.
with those of R. That because X-rays can only detect the crystallite parts inside the nanoparticle, whereas TEM gives complete picture of the nanoparticle and can measure the individual nanoparticle size. It is presented that Z has the same behavior of R and decreases with x. This decrease may ascribe to the substitution process and improving the crystallization process. 3.3. FT-IR infrared (IR) absorption spectra IR absorption spectra of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites recorded in the range 200–2000 cm 1 are seen in Fig. 8. Seven absorption bands; ν1, ν2, ν3, ν4, νA, νB and νT are observed in IR spectra and assigned to the M-type barium ferrite [16]. The observed band positions are presented in Table 2. Table 2 presents that the characteristic bands of M-type hexaferrites ν1, ν2 and ν3 are observed in all IR spectra; ν1 in the range of 580.6–586.35 cm 1, ν2 in the range of 433.97–439.76 cm 1 and ν3 in the range of 333.7–337.6 cm 1. The band ν1 is assigned to intrinsic stretching vibrations of the tetrahedral A-site metal ionoxygen bonding corresponding to the highest restoring force and ν2 to intrinsic vibrations of the octahedral B-site complexes with
lower wave number which are bond-bending vibrations [14,19,20]. The band ν3 depends on the mass of the divalent tetrahedral cation and is assigned to the divalent octahedral metal ion-oxygen ion complexes [16]. The values of ν1 are higher compared to ν2, which indicate that the normal mode of vibration of the A-sites is higher than that of the B-sites. This is attributed to shorter bond length of the A-site clusters than that of the B-site clusters [14]. The band ν4 is observed in the range of 231.5–237.3 cm 1 and depends on the mass of the tetrahedral divalent cation. It is assigned to some type of vibrations involving a displacement of the tetrahedral cation [14,16]. The bands νA and νB appear in the spectra at around 880 and 1010 cm 1, respectively. These bands are assigned to the intrinsic vibrations of the A-site group. The band νA can assign to increase in the concentration of divalent metallic ions Fe2 þ and/or Ba2 þ among the A-sites. The band νB represents the tetravalent metaloxygen vibrations and may assign to the existence of the complexes Ti4 þ –O2 and/or Fe4 þ –O2 among the A-sites [14]. Small splitting of the characteristic peaks are observed and assigned to the vibrations of the divalent metal ion-oxygen complexes among the A- and B-sites and/or the formation of
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Fig. 11. DTA curves for BaTixFe12 4/3xO19 M-type hexagonal nano-ferrites.
tetrahedral and octahedral clusters at these sites [16]. A triple band νT appears at around 1550 cm 1 may ascribe to the residual humidity in the samples [14]. Debye temperature ΘD was calculated using the following relation [21]:
ΘD =
ℏCνav = 1.438νav k
νAV =
ν1 + ν2 + ν3 3
where νav is the average value of wave numbers, ħ¼h/2π, h is Plank’s constant, k is Boltzmann’s constant, C ¼3 1010 cm/s; C is the velocity of light, where the value of ℏC/k for the ferrite materials taken as 1.438 [14,21–23]. Fig. 9 shows variation of ΘD versus Ti4 þ ion content x. It is shown that the trend of ΘD values increases against x. The variation of ΘD may be due to the variation of the wave number of IR bands [21,23]. This variation can be understood using the specific heat theory which explains that the conduction electrons can absorb part of the heat causing a decrease in ΘD . Consequently, the increasing trend of ΘD proves
decrease of the conduction electrons (i.e. n-type) and increase of the contribution holes (i.e. p-type) as x increases [21–23]. The threshold frequency νTh of the transition electrons can be determined by the maximum point of IR spectrum. The relation between νTh and x is shown in Fig. 9. It is shown that the trend of νTh deceases against x which proves decrease of conduction electrons (n-type) in the samples and enhances the variation of ΘD. It is known that the force constant Fc is proportional to the Fe3 þ –O2 band frequency at the tetrahedral A- and octahedral B-sites. Therefore, the force constant Fc can be calculated by using the relation [14,24–27];
Fc = 4π 2c 2ν 2m where m is the reduced mass of Fe and O ions, m ¼2.061 10 23 g. The force constants F1 and F2 of the A- and B-sites, respectively, are presented in Table 2. It is presented that F2 increases nonmonotonically with x to a maximum value at x¼ 0.5 and decreases thereafter, whereas the trend of F1 increases. This confirms the dependence of F1 and F2 on Ti4 þ ion content x and vibration frequency at these sites. Variation of F1 and F2 with x
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Fig. 12. RT magnetic hysteresis loops of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites. Table 3 The magnetic parameters; Hc is the coercivity, Mr the remanent magnetization, Mr/ Ms the squareness, nB the magnetic moment and K the anisotropy constant, error¼ 7 0.03. x 0 0.125 0.25 0.375 0.5 0.75 1 Fig. 13. Variation of saturation magnetization Ms and coercivity Hc with Ti4 þ ion content x.
may result from the formation of nano-clusters, increase of porosity and substitution process [14]. 3.4. Thermal analysis Thermo-gravimetric analysis (TGA) of M-type hexagonal
Hc (Gauss)
Mr (emu/g)
Mr/Ms
nB (μB)
K (erg/Gauss)
677.49 456.07 663.69 777.88 484.74 900.71 840.2
22.02 15.6 22.24 19.63 15.94 18.46 20.8
0.39 0.27 0.4 0.39 0.32 0.41 0.46
11.38 11.34 10.1 9.84 9.7 8.86 8.79
40362.17 27153.74 38424.19 40408.44 24906.04 42535.09 39578.67
BaTixFe12 4/3xO19 nanoferrites, x ¼0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1, were carried out in the range from room temperature (RT) up to 1000 °C. Fig. 10 displays the taken TGA curves which indicate three distinct steps of weight loss. (1) The first step, when the temperature was increased from RT up to 360 °C. The TGA curve show an increase in the sample weight between 0.0008% and 0.0042% weight at E50 °C. This weight gain proves existence of oxygen vacancies in the nanoferrite samples [12], where they can absorb oxygen atoms from the atmosphere to reach their
M.A. Amer et al. / Materials Science in Semiconductor Processing 40 (2015) 374–382
Fig. 14. The effect of porosity P and crystallite size R on the saturation magnetization Ms.
maximum weight. Thereafter, the curves show a gradual decrease of weight with increasing temperature. The gradual weight loss before 100 °C is attributed to the volatilization of the residual humidity in the samples [28], which is confirmed by small endothermic transformation between room temperature and 100 °C by DTA curves as shown in Fig. 11 [29]. The combustion curves show another small endothermic transformation between 210 and 360 °C which is ascribed to the evaporation of other residual humidity [20,30,31]. (2) The second step of weight loss is seen in the TGA curves (Fig. 10) in the range of 450–510 °C. This peak is correlated to the thermal decomposition of the BaTixFe12 4/3xO19 nano-ferrites into oxides which is confirmed by existence of a broad exothermic peak as seen in the DTA curves (Fig. 11) at 430–520 °C [29,30]. This suggests that the nucleation of the BaTixFe12 4/3xO19 nano-ferrites may occur at different temperatures [29,30]. (3) The third weight loss can be seen in TGA and DTA curves (Figs. 10 and 11) which show broad exothermic peak up to 600 °C. This may result from the formation and improvement of crystallization process of the BaTixFe12 4/3xO19 M-type nano-ferrite phase [1,20,32–34]. The TGA curves proved that the net weight loss of the samples heated from RT up to 1000 °C lies in the range of 0.00418– 0.01834% weight, where the maximum weight loss occurs before heating at 500 °C [6]. There is no noticeable weight loss by heating above 1000 °C, which most likely due to the onset of BaTixFe12 4/ 3xO19 nano-ferrites phase [34].
381
randomly but its trend show an increase. It is known that Ms originates from the spin rotation, domain walls movement and A– B magnetic super-exchange interactions. The super-exchange interactions depend on the distribution of magnetic Fe3 þ ions among the crystal sublattices [10]. The decrease of Ms may assign to the substitution of diamagnetic Ti4 þ ions for Fe3 þ ions which causes a decrease of A–B super-exchange interactions, i.e. the magnetic Fe3A þ –O2–Fe3B þ bond number. The substitution of the diamagnetic Ti4 þ ion instead of the magnetic Fe3 þ ion (5.9 μB) causes increase in the coercivity Hc (Table 3) and reduction in saturation magnetization Ms. Thus, the remanent magnetization (Mr) decrease may be due to the weakening of the super-exchange magnetic interaction of Fe3 þ –O–Fe3 þ bonds in the ferrimagnetic barium ferrite [10,16]. The obtained Mr values are given in Table 3. Variation of Mr with x shows a decreasing trend which may be due to the substitution process and that the individual grains act as a magnetic material and produce magnetization [14]. The increase of Hc is attributed to the increase in anisotropy field, since the coercivity is proportional to the magnetic anisotropy field. The measured Hc values are listed in Table 3. Furthermore, the enhancement of coercivity is due to small grain sizes [6,14]. The obtained values of the anisotropy constant (K) are listed in Table 3. The surface effects of fine nanoparticles are dominant, therefore the surface spins also affect the magnetization and anisotropy energy [14]. The increase in Hc and decrease in Ms with x enhance the variation of the anisotropy constant K, as well as the effect of spin canting [14]. Also, high concentrations of the non-magnetic Ti4 þ ions cause weakening of the inter-sublattice interactions where weaker coupling causes the decrease of the anisotropy energy and consequently K [14]. The anisotropy constant (K) covers all sources of the anisotropy energy, as magneto-crystalline, shape and surface anisotropies [14]. The magnetic moment (nB) per formula unit in Bohr magneton (μB) could be calculated using the following relation [14,16]:
nB =
M × MS 5585
where M is the molecular weight of each particular composition and Ms is the saturation magnetization. The obtained values of magnetic moment are presented in Table 3. It is presented that nB decreases with x, which may assign to the decrease in Ms [35]. As the crystallite size R decreases and the spin canting angle increases, Ms and nB decrease, as well as the reduced strength of A–B super-exchange magnetic interactions [14,16]. The squareness, i.e. the ratio of the remanent magnetization (Mr) to Ms (Mr/Ms), is an important characteristic parameter for applications for ferro/ferri-magnetic materials. The calculated values of Mr/Ms are listed in Table 3. It is clear that the trend of Mr/Ms values slowly increases against x which may attribute to variation of K, Hc and Ms [14]. Basically, Ms is affected by the porosity P and crystallite size R [14]. Fig. 14(a) shows the relation between Ms and P. It is displayed that Ms decreases as P increases which confirms the dependence of Ms on P [14]. The dependence of Ms on R is seen in Fig. 14(b). It is seen that Ms increases with R and this is reasonable at which the spin canting angle decreases with increasing R [14,16].
3.5. Magnetic hysteresis loops 4. Conclusion RT magnetic hysteresis loops of M-type hexagonal BaTixFe12 4/ 3xO19 nanoferrites are depicted in Fig. 12. It is depicted that the curves have a wide hysteretic behavior (high coercivity Hc) which is characteristic of hard magnetic materials [1,4–6,25]. Fig. 13 displays the variation of deduced saturation magnetization (Ms) against x. It is displayed that Ms decreases against x, whereas the recorded values of coercivity Hc (Table 3) changes
M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles, 0.0 rx r1, were prepared by co-precipitation route and annealing at 1200 °C for 20 h. The results revealed that all samples have single M-type hexagonal phase structure (magnetoplumbite structure). The average particle size ranged 42.35–61.30 nm and is a little higher than the crystallite size R where they showed decrease with Ti4 þ
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content x. Seven absorption bands ν1, ν2, ν3, ν4, νA, νB and νT were observed in the IR spectra and assigned to their corresponding sites and bonds. They pointed to the existence of the ions Fe2 þ and Fe4 þ in the crystal sublattices. The lattice constants, density, porosity (P), strain (ε), specific surface area, crystallite size (R), IR absorption band positions, threshold frequency, Debye temperature, saturation magnetization (Ms), remanent magnetization, coercivity, squareness and magnetic moment were affected by Ti4 þ ion concentration x. VSM curves displayed wide hysteretic behaviors with higher coercivity which is characteristic of the typical hard magnetic materials, and this is a very desirable characteristic for recording media. Ms and ε proved dependence on P and R. The net weight loss of the samples heated from room temperature up to 1000 °C led in the range of 0.00418–0.01834% weight, where the maximum weight loss occurred before heating temperature 500 °C. Heating the samples above 1000 °C did not show a noticeable weight loss, which most likely may due to the onset of BaTixFe12 4/3xO19 nano-ferrites phase.
Acknowledgment The authors are grateful to the council of Tanta University for supporting the current research project under the code number 01-13-05.
References [1] S.P. Gairola, V. Verma, A. Singh, L.P. Purohit, R.K. Kotnala, Solid State Commun. 150 (2010) 147. [2] A. Goldman, Modern Ferrite Technology, Marcel Dekker Inc., New York, 1993. [3] Y. Liu, M.G.B. Drew, Y. Liu, J. Magn. Magn. Mater. 323 (2011) 945. [4] S.M. El-Sayed, T.M. Meaz, M.A. Amer, H.A. ElShersaby, Physica B 426 (2013) 137. [5] J. Dho, E.K. Lee, J.Y. Park, N.H. Hur, J. Magn. Magn. Mater. 285 (2005) 164. [6] S. Ounnunkad, P. Winotai, J. Magn. Magn. Mater. 301 (2006) 292. [7] M.A. Amer, T.M. Meaz, S.S. Attalah, A.I. Ghoneim, J. Magn. Magn. Mater. 363 (2014) 60. [8] B.D. Cullity, Elements of X-ray Differaction, second edition,. Addison-wesley puplishing company, Inc., USA, 1978.
[9] S.A. Safaan, A.M. Abo El Ata, M.S. El Messeery, J. Magn. Magn. Mater. 302 (2006) 362. [10] Y. Liu, M.G.B. Drew, J. p. Wang, M. Zhang, Y. Liu, J. Magn. Magn. Mater. 322 (2010) 366. [11] C. Wang, X. Qi, L. Li, Ji Zhou, X. Wang, Z. Yue, Mater. Sci. Eng. B 99 (2003) 270. [12] G. Dixit, J.P. Singh, R.C. Srivastava, H.M. Agrawal, J. Magn. Magn. Mater. 324 (2012) 479. [13] P.P. Hankare, R.P. Patil, U.B. Sankpal, S.D. Jadhav, I.S. Mulla, K.M. Jadhav, B. K. Chougule, J. Magn. Magn. Mater. 321 (2009) 3270. [14] M.A. Amer, T.M. Meaz, A.G. Mostafa, H.F. El-Ghazally, Mater. Sci. Semicond. Process. 32 (2015) 68. [15] E.C. Subfarao, J. Am. Ceram. Soc. 43 (1960) 119. [16] D.H. Bobade, S.M. Rathod, M.L. Mane, Physica B 407 (2012) 3700. [17] E. Ranjith Kumar, R. Jayaprakash, Sanjay Kumar, J. Magn. Magn. Mater. 351 (2014) 70. [18] Ping Hu, Hai-bo Yang, De-an Pan, Hua Wang, Jian-jun Tian, Shen-gen Zhang, Xin-feng Wang, Alex A. Volinsky, J. Magn. Magn. Mater. 322 (2010) 173. [19] M. Ahmad, I. Ali, R. Grossinger, M. Kriegisch, F. Kubel, M.U. Rana, J. Alloy. Compd. 579 (2013) 57. [20] M. Ahmad, R. Grössinger, M. Kriegisch, F. Kubel, M.U. Rana, J. Magn. Magn. Mater. 332 (2013) 137. [21] S.M. Patange, S.E. Shirsath, K.S. Lohar, S.G. Algude, S.R. Kamble, N. Kulkarni, D. R. Mane, K.M. Jadhav, J. Magn. Magn. Mater. 325 (2013) 107. [22] S.M. Patange, Sagar E. Shirsath, S.P. Jadhav, V.S. Hogade, S.R. Kamble, K. M. Jadhav, J. Mol. Struct. 1038 (2013) 40. [23] S.A. Mazen, S.F. Mansour, E. Dhahri, H.M. Zaki, T.A. Elmosalami, J. Alloy. Compd. 470 (2009) 294. [24] M.A. Amer, T.M. Meaz, A.G. Mostafa, M. El-Kastawy, A.I. Ghoneim, Ceram. Int. 40 (2014) 241. [25] G.B. Teh, S. Nagalingam, D.A. Jefferson, Mater. Chem. Phys. 101 (2007) 158. [26] P.P. Hankare, V.T. Vader, N.M. Patil, S.D. Jadhav, U.B. Sankpal, M.R. Kadam, B. K. Chougule, N.S. Gajbhiye, Mater. Chem. Phys. 113 (2009) 233. [27] M. Sivakumar, A. Towata, K. Yasui, T. Tuziuti, T. Kozuka, Y. Iida, M.M. Maiorov, E. Blums, D. Bhattacharya, N. Sivakumar, M. Ashok, Ultrason. Sonochem. 19 (2012) 652. [28] R. Gimenes, M.R. Baldissera, M.R.A. da Silva, C.A. DA Silveira, D.A.W. Soares, L. A. Perazolli, M.R. da Silva, M.A. Zaghete, Ceram. Int. 38 (2012) 741. [29] R.A. Khan, S. Mir, A.M. Khan, B. Ismail, Abdur Rahman Khan, Ceram. Int. 40 (2014) 11205. [30] F. Song, X. Shen, M. Liu, Jun Xiang, Solid State Sci. 12 (2010) 1603. [31] J. Bursik, Ivo Drbohlav, Z. Frait, K. Knizek, R. Kuzel, K. Kouril, J. Solid State Chem. 184 (2011) 3085. [32] I. Ali, M.U. Islam, M.S. Awan, M. Ahmad, M.N. Ashiq, S. Naseem, J. Alloy. Compd. 550 (2013) 564. [33] M.A. Gabal, R.S. Al-luhaibi, Y.M. Al Angari, J. Hazard. Mater. 246–247 (2013) 227. [34] S. Kracunovska, J. Töpfer, J. Magn. Magn. Mater. 320 (2008) 1370. [35] V. Kumar, A. Rana, M.S. Yadav, R.P. Pant, J. Magn. Magn. Mater. 320 (2008) 1729.
Contents lists available at ScienceDirect
Materials Science in Semiconductor Processing journal homepage: www.elsevier.com/locate/matsci
Structural and magnetic studies of Ti4 þ substituted M-type BaFe12O19 hexa-nanoferrites M.A. Amer a,n, T.M. Meaz a, S.S. Attalah b, A.I. Ghoneim a a b
Physics Department, Faculty of Science, Tanta University, 31527 Tanta, Egypt Reactor and Neutron Physics Department, Nuclear Research Center, Cairo, Egypt
art ic l e i nf o
a b s t r a c t
Article history: Received 19 April 2015 Received in revised form 5 July 2015 Accepted 6 July 2015
M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles, 0 r x r1, were prepared by the chemical co-precipitation method. XRD, TEM, FT-IR, TGA, DTA and VSM techniques were used to characterize the samples. This study proved the formation of single-phase M-type hexagonal nanoferrites. The average particle and crystallite (R) sizes, lattice parameter c, experimental and theoretical densities, strain (ε), saturation magnetization (Ms), magnetic moment showed decrease against x, whereas the lattice constant a, porosity (P) and specific surface area showed increase. The force constants and trend of band positions and Debye temperature were x dependent, whereas the coercivity, remanent magnetization, squareness and anisotropy constant did not. The net weight loss of the samples led in the range of 0.00418–0.01834% weight where the maximum weight loss occurred before heating at 500 °C. P and R showed strong effect on Ms and ε. & 2015 Elsevier Ltd. All rights reserved.
Keywords: BaTixFe12 (4/3)xO19 nanoparticles Structural and magnetic properties Thermal analysis
1. Introduction Recently, advanced researches have greatly devoted to develop new nanomaterials for applications in the fields of shielding technology, recording material due to their large magneto-crystalline anisotropy, relatively high saturation magnetization, nontoxicity, excellent chemical stability and good corrosion resistivity [1,2]. The fine particle size, high specific surface area, high and hard magnetization and chemical homogeneity of nanoparticles are required for important technological applications. In addition, hexagonal nanoferrites are candidate materials as a radar absorbing material due to their high permeability, magnetization and other good dielectric properties. Furthermore, hexagonal ferrites are hard-magnetic magnets with high saturation magnetization and maximum coercivity which make them highly recommended for such applications. M-type hexagonal nanoferrites have been investigated intensively due to their fine particle size, high specific surface area and good chemical and thermal stability. Their magnetoplumbite structure of general formula MFe12O19 (M ¼ Ba, Sr) is an appropriate candidate for several applications such as permanent magnet and recording media [2]. Many researchers prepared M-type hexagonal nanoferrites with different substituted ions using different preparation n
Corresponding author. Fax: þ20 403350804. E-mail addresses: [email protected], [email protected] (M.A. Amer). http://dx.doi.org/10.1016/j.mssp.2015.07.007 1369-8001/& 2015 Elsevier Ltd. All rights reserved.
methods and characterized the obtained samples by different techniques [3–6]. The crystallite and grain sizes, structural and lattice parameters, saturation magnetization, coercivity, magneton number, microstrain and dislocation density of the nanoferrites were affected by the preparation conditions, thermal treatments and substitution process. The obtained results were discussed depending on accumulated data and comparing with the bulk materials. This investigation is devoted to synthesize M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles by the chemical co-precipitation method. The samples were characterized using X-ray diffraction, transmission electron microscopy, Fourier transform infrared spectroscopy, thermo gravimetric and differential thermal analysis and vibrating sample magnetometry.
2. Experimental 2.1. Sample preparation M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles, x¼ 0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1 were prepared by the chemical co-precipitation method according to the equation [7]; Ba(NO3)2 þxTi(C12H28O4)þ (12–(4)/(3)x)Fe(NO3)3 9H2Oþ (38 4x) NaOH-BaTixFe12 (4/3)xO19 þ(38 4x)NaNO3 þ4x(CH3)2CHOHþ (127 16x)H2O
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375
Fig. 5. Variation of the specific surface area S and strain ε against x.
Fig. 1. XRD patterns of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites.
Fig. 2. Dependence of the lattice constants a and c on Ti4 þ ion content x.
Fig. 6. Dependence of strain ε on the crystallite size R and porosity P.
Fig. 3. Variation of the crystallite size R against x.
Fig. 4. Variation of the density D, theoretical density Dx, and porosity P with x.
Stoichiometric proportion amounts of the high purity Ba(NO3)2, Ti(C12H28O4) and Fe(NO3)3 9H2O were dissolved in distilled water and kept in about 10 °C for one hour (h). The reactants were mixed
and constantly stirred using a magnetic stirrer for 10 min. The NaOH solution was added drop wise where the pH of mixed solution was constantly monitored as pH E13. Then the solution was heated and maintained at 90 °C for 2 h under continuous stirring till the precipitation occurred. The precipitates were thoroughly washed with distilled water until the washings become free from sodium chloride. The precipitates were dried for a few days at room temperature. Then the samples were thoroughly ground in an agate mortar to obtain fine powder. Thereafter, the samples were annealed for 20 h at 1200 °C and then slowly cooled to room temperature. The samples were ground to fine powder and annealed again at 1200 °C for 20 h and then slowly cooled to room temperature. Finally, the nanoparticle samples were ground to fine powder. 2.2. Measurements The nanoparticle samples were characterized by X-ray diffraction using GNR APD 2000 Pro X-ray diffractometer step scan type and CuKα1 radiation at wavelength λ ¼1.540598 Å. The lattice
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Fig. 7. TEM images for the BaTixFe12 4/3xO19 nanoferrites.
Table 1 The average particle size (Z) of BaTixFe12 4/3xO19 nanoferrites; error¼ 7 0.2. x Z (nm)
0.0 61.3
0.125 60.5
0.25 56.6
0.375 52
0.5 50
0.75 42.4
1 46.3
constants a and c were calculated using the relations [8]:
1 4 ⎛ h2 + hk + k 2 ⎞ l2 ⎟+ 2 = ⎜ 2 2 3⎝ dhkl a ⎠ c ⎡ ⎛ A1B − AB1 ⎢4 a=⎢ ⎜ 3 ⎜⎝ B/d12 − B1/d2 ⎣
(
⎡ A B − AB ⎤1/2 1 ⎥ c=⎢ 12 ⎣ A1/d − A/d12 ⎦
)
1/2 ⎞⎤ ⎟⎥ ⎟⎥ ⎠⎦
Fig. 8. IR absorption spectra of the M-type hexagonal BaTixFe12 (4/3)xO19 nanoferrites.
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377
Table 2 IR absorption band positions νn, n¼ 1, 2,… and T, and force constants F1 and F2, error¼ 7 0.02. x 0 0.125 0.25 0.375 0.5 0.75 1
ν1 (cm 1)
ν2 (cm 1)
ν3 (cm 1)
ν4 (cm 1)
νA (cm 1)
νB (cm 1)
F1n105 (dyne/cm)
F2n105 (dyne/cm)
582.50 584.42 584.58 580.56 584.43 582.49 586.35
435.90 433.97 437.83 435.95 439.76 437.78 435.98
335.60 333.68 335.63 335.65 335.69 337.57 337.40
231.50 237.20 237.21 237.22 237.23 237.24 237.25
885.30 896.87 871.80 869.85 889.16 883.38 877.59
1022.25 1016.50 1006.82 1001.03 1004.89 1010.67 1020.32
2.49 2.5 2.5 2.47 2.5 2.48 2.52
1.39 1.38 1.4 1.39 1.42 1.4 1.4
Fig. 9. Dependence of Debye temperature �D and threshold frequency νth on x.
where d is the interplaner distance, A¼ h2 þhþ k2; B ¼l2 and A1 = h12 + h1k1 + k12 ; B1=l12 . The crystallite size R was determined using the prominent diffraction peak (107) and Scherrer’s formula [8]:
R=
0.9λ β1/2 cos θ
where K ¼0.9 and β1/2 is the full width at half maximum of the peak (107). The porosity (P) of the samples was calculated using the equation [9]:
P=1−
D Dx
The obtained values of lattice constant a lie in the range of 5.8782–5.902 Å and c in the range of 23.1061–23.1636 Å where c/ aE 3.921 which agree with the published data [3,12]. The values of a and c are plotted against x as seen in Fig. 2. It is seen that c decreases with x, whereas a increases which can attribute to the substitution of the larger ionic radius Fe3 þ ions (0.64 Å) by Ti4 þ ions (0.61 Å) [3,12]. The determined crystallite size R values lie in the range of 41.4– 59.1 nm as illustrated in Fig. 3. It is illustrated that R decreases with x which may ascribe to the substitution process and improving the crystallization process [13,14]. Variation of the sample experimental density D, theoretical density (X-ray density) Dx and porosity P against x is displayed in Fig. 4. It is displayed that Dx and D decrease with x, whereas P increases. The decrease of Dx and D is attributed to the substitution of larger atomic weight Fe3 þ ions (55.85) by Ti4 þ ions (47.9). The increase in P with x may point to increase in oxygen vacancies which play a predominant role in densification and packing of the samples and may assign to that D decreases more than Dx [9,15]. The specific surface area (S) and strain (ε) were calculated using the equations [12,13]:
β1/2 cos θ = S=
0.9λ + 4ε sin θ R
6000 RDx
where D and Dx are the experimental and theoretical (X-ray) densities, respectively. The average nanoparticle size was determined by using JEOL JEM–100 SX transmission electron microscope. Infrared absorption spectra of the samples were recorded in the range of 200– 2000 cm 1 using a Bruker Tensor 27 FT-IR spectrometer. Simultaneous thermo gravimetric analysis (TGA) and differential thermal analysis (DTA) of the nanoferrite samples were carried out in N2-atmosphere using an Perkin-Elmer STA 6000 thermal analysis system at heating rate of 15 °C/min. Hysteresis loops of the samples were recorded at room temperature using the vibrating sample magnetometer (LDJ) Electronic Inc. Troy, MI and a maximum applied field up to 25,000 Gauss.
The graph of β1/2 cos θ against 4sin θ shows a straight line whose slope gives the value of ε. Fig. 5 illustrates variation of S and ε with x. It is illustrated that S increases with x, whereas ε decreases. The increase of S is attributed to decrease in R and D. When the nanoparticle has smaller crystallite size that means it has a larger specific surface area [12]. The decrease of ε may be assigned to decreasing R where the negative strain values prove compressive strain [12–14,16]. The decrease of strain indicates the mechanical properties of samples such as the stability of nanostructure, adhesion between and/or within the nanoparticles and grain hardness. The decrease of ε enhances the decreases of R and increase of S where they prove the decrease of lattice volume [12– 14,16]. The dependence of ε on R and P is clear in Fig. 6 which indicates that ε increases against R and decreases against P.
3. Results and discussion
3.2. Transmission electron microscope (TEM) images
3.1. X-ray diffraction (XRD) analysis
TEM images of BaTixFe12 4/3xO19 nanoferrites are depicted in Fig. 7. It is depicted that the nanoparticles are agglomerated to each other where the nanoparticles for x Z0.75 are something granular. The agglomeration occurs and increases at higher annealing temperature which causes increase of the interaction between magnetic particles [17,18]. The obtained average values of nanoparticle size (Z) are listed in Table 1. Table 1 presents that the Z values are a little higher compared
Fig. 1 shows the XRD patterns of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites, x¼ 0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1. It is shown that the reflection planes (110), (107), (114), (203), (205), (217), (2011) and (220) appear in all the spectra which proves that the samples have a single-phase M-type hexagonal structure [10,11], as compared with JCPDS data (Card nos. 00-027-1029, 00-007-0276 and 01-079-1411).
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Fig. 10. TGA curves for M-type hexagonal BaTixFe12 4/3xO19 nano-ferrites.
with those of R. That because X-rays can only detect the crystallite parts inside the nanoparticle, whereas TEM gives complete picture of the nanoparticle and can measure the individual nanoparticle size. It is presented that Z has the same behavior of R and decreases with x. This decrease may ascribe to the substitution process and improving the crystallization process. 3.3. FT-IR infrared (IR) absorption spectra IR absorption spectra of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites recorded in the range 200–2000 cm 1 are seen in Fig. 8. Seven absorption bands; ν1, ν2, ν3, ν4, νA, νB and νT are observed in IR spectra and assigned to the M-type barium ferrite [16]. The observed band positions are presented in Table 2. Table 2 presents that the characteristic bands of M-type hexaferrites ν1, ν2 and ν3 are observed in all IR spectra; ν1 in the range of 580.6–586.35 cm 1, ν2 in the range of 433.97–439.76 cm 1 and ν3 in the range of 333.7–337.6 cm 1. The band ν1 is assigned to intrinsic stretching vibrations of the tetrahedral A-site metal ionoxygen bonding corresponding to the highest restoring force and ν2 to intrinsic vibrations of the octahedral B-site complexes with
lower wave number which are bond-bending vibrations [14,19,20]. The band ν3 depends on the mass of the divalent tetrahedral cation and is assigned to the divalent octahedral metal ion-oxygen ion complexes [16]. The values of ν1 are higher compared to ν2, which indicate that the normal mode of vibration of the A-sites is higher than that of the B-sites. This is attributed to shorter bond length of the A-site clusters than that of the B-site clusters [14]. The band ν4 is observed in the range of 231.5–237.3 cm 1 and depends on the mass of the tetrahedral divalent cation. It is assigned to some type of vibrations involving a displacement of the tetrahedral cation [14,16]. The bands νA and νB appear in the spectra at around 880 and 1010 cm 1, respectively. These bands are assigned to the intrinsic vibrations of the A-site group. The band νA can assign to increase in the concentration of divalent metallic ions Fe2 þ and/or Ba2 þ among the A-sites. The band νB represents the tetravalent metaloxygen vibrations and may assign to the existence of the complexes Ti4 þ –O2 and/or Fe4 þ –O2 among the A-sites [14]. Small splitting of the characteristic peaks are observed and assigned to the vibrations of the divalent metal ion-oxygen complexes among the A- and B-sites and/or the formation of
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379
Fig. 11. DTA curves for BaTixFe12 4/3xO19 M-type hexagonal nano-ferrites.
tetrahedral and octahedral clusters at these sites [16]. A triple band νT appears at around 1550 cm 1 may ascribe to the residual humidity in the samples [14]. Debye temperature ΘD was calculated using the following relation [21]:
ΘD =
ℏCνav = 1.438νav k
νAV =
ν1 + ν2 + ν3 3
where νav is the average value of wave numbers, ħ¼h/2π, h is Plank’s constant, k is Boltzmann’s constant, C ¼3 1010 cm/s; C is the velocity of light, where the value of ℏC/k for the ferrite materials taken as 1.438 [14,21–23]. Fig. 9 shows variation of ΘD versus Ti4 þ ion content x. It is shown that the trend of ΘD values increases against x. The variation of ΘD may be due to the variation of the wave number of IR bands [21,23]. This variation can be understood using the specific heat theory which explains that the conduction electrons can absorb part of the heat causing a decrease in ΘD . Consequently, the increasing trend of ΘD proves
decrease of the conduction electrons (i.e. n-type) and increase of the contribution holes (i.e. p-type) as x increases [21–23]. The threshold frequency νTh of the transition electrons can be determined by the maximum point of IR spectrum. The relation between νTh and x is shown in Fig. 9. It is shown that the trend of νTh deceases against x which proves decrease of conduction electrons (n-type) in the samples and enhances the variation of ΘD. It is known that the force constant Fc is proportional to the Fe3 þ –O2 band frequency at the tetrahedral A- and octahedral B-sites. Therefore, the force constant Fc can be calculated by using the relation [14,24–27];
Fc = 4π 2c 2ν 2m where m is the reduced mass of Fe and O ions, m ¼2.061 10 23 g. The force constants F1 and F2 of the A- and B-sites, respectively, are presented in Table 2. It is presented that F2 increases nonmonotonically with x to a maximum value at x¼ 0.5 and decreases thereafter, whereas the trend of F1 increases. This confirms the dependence of F1 and F2 on Ti4 þ ion content x and vibration frequency at these sites. Variation of F1 and F2 with x
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Fig. 12. RT magnetic hysteresis loops of M-type hexagonal BaTixFe12 4/3xO19 nanoferrites. Table 3 The magnetic parameters; Hc is the coercivity, Mr the remanent magnetization, Mr/ Ms the squareness, nB the magnetic moment and K the anisotropy constant, error¼ 7 0.03. x 0 0.125 0.25 0.375 0.5 0.75 1 Fig. 13. Variation of saturation magnetization Ms and coercivity Hc with Ti4 þ ion content x.
may result from the formation of nano-clusters, increase of porosity and substitution process [14]. 3.4. Thermal analysis Thermo-gravimetric analysis (TGA) of M-type hexagonal
Hc (Gauss)
Mr (emu/g)
Mr/Ms
nB (μB)
K (erg/Gauss)
677.49 456.07 663.69 777.88 484.74 900.71 840.2
22.02 15.6 22.24 19.63 15.94 18.46 20.8
0.39 0.27 0.4 0.39 0.32 0.41 0.46
11.38 11.34 10.1 9.84 9.7 8.86 8.79
40362.17 27153.74 38424.19 40408.44 24906.04 42535.09 39578.67
BaTixFe12 4/3xO19 nanoferrites, x ¼0, 0.125, 0.25, 0.375, 0.5, 0.75 and 1, were carried out in the range from room temperature (RT) up to 1000 °C. Fig. 10 displays the taken TGA curves which indicate three distinct steps of weight loss. (1) The first step, when the temperature was increased from RT up to 360 °C. The TGA curve show an increase in the sample weight between 0.0008% and 0.0042% weight at E50 °C. This weight gain proves existence of oxygen vacancies in the nanoferrite samples [12], where they can absorb oxygen atoms from the atmosphere to reach their
M.A. Amer et al. / Materials Science in Semiconductor Processing 40 (2015) 374–382
Fig. 14. The effect of porosity P and crystallite size R on the saturation magnetization Ms.
maximum weight. Thereafter, the curves show a gradual decrease of weight with increasing temperature. The gradual weight loss before 100 °C is attributed to the volatilization of the residual humidity in the samples [28], which is confirmed by small endothermic transformation between room temperature and 100 °C by DTA curves as shown in Fig. 11 [29]. The combustion curves show another small endothermic transformation between 210 and 360 °C which is ascribed to the evaporation of other residual humidity [20,30,31]. (2) The second step of weight loss is seen in the TGA curves (Fig. 10) in the range of 450–510 °C. This peak is correlated to the thermal decomposition of the BaTixFe12 4/3xO19 nano-ferrites into oxides which is confirmed by existence of a broad exothermic peak as seen in the DTA curves (Fig. 11) at 430–520 °C [29,30]. This suggests that the nucleation of the BaTixFe12 4/3xO19 nano-ferrites may occur at different temperatures [29,30]. (3) The third weight loss can be seen in TGA and DTA curves (Figs. 10 and 11) which show broad exothermic peak up to 600 °C. This may result from the formation and improvement of crystallization process of the BaTixFe12 4/3xO19 M-type nano-ferrite phase [1,20,32–34]. The TGA curves proved that the net weight loss of the samples heated from RT up to 1000 °C lies in the range of 0.00418– 0.01834% weight, where the maximum weight loss occurs before heating at 500 °C [6]. There is no noticeable weight loss by heating above 1000 °C, which most likely due to the onset of BaTixFe12 4/ 3xO19 nano-ferrites phase [34].
381
randomly but its trend show an increase. It is known that Ms originates from the spin rotation, domain walls movement and A– B magnetic super-exchange interactions. The super-exchange interactions depend on the distribution of magnetic Fe3 þ ions among the crystal sublattices [10]. The decrease of Ms may assign to the substitution of diamagnetic Ti4 þ ions for Fe3 þ ions which causes a decrease of A–B super-exchange interactions, i.e. the magnetic Fe3A þ –O2–Fe3B þ bond number. The substitution of the diamagnetic Ti4 þ ion instead of the magnetic Fe3 þ ion (5.9 μB) causes increase in the coercivity Hc (Table 3) and reduction in saturation magnetization Ms. Thus, the remanent magnetization (Mr) decrease may be due to the weakening of the super-exchange magnetic interaction of Fe3 þ –O–Fe3 þ bonds in the ferrimagnetic barium ferrite [10,16]. The obtained Mr values are given in Table 3. Variation of Mr with x shows a decreasing trend which may be due to the substitution process and that the individual grains act as a magnetic material and produce magnetization [14]. The increase of Hc is attributed to the increase in anisotropy field, since the coercivity is proportional to the magnetic anisotropy field. The measured Hc values are listed in Table 3. Furthermore, the enhancement of coercivity is due to small grain sizes [6,14]. The obtained values of the anisotropy constant (K) are listed in Table 3. The surface effects of fine nanoparticles are dominant, therefore the surface spins also affect the magnetization and anisotropy energy [14]. The increase in Hc and decrease in Ms with x enhance the variation of the anisotropy constant K, as well as the effect of spin canting [14]. Also, high concentrations of the non-magnetic Ti4 þ ions cause weakening of the inter-sublattice interactions where weaker coupling causes the decrease of the anisotropy energy and consequently K [14]. The anisotropy constant (K) covers all sources of the anisotropy energy, as magneto-crystalline, shape and surface anisotropies [14]. The magnetic moment (nB) per formula unit in Bohr magneton (μB) could be calculated using the following relation [14,16]:
nB =
M × MS 5585
where M is the molecular weight of each particular composition and Ms is the saturation magnetization. The obtained values of magnetic moment are presented in Table 3. It is presented that nB decreases with x, which may assign to the decrease in Ms [35]. As the crystallite size R decreases and the spin canting angle increases, Ms and nB decrease, as well as the reduced strength of A–B super-exchange magnetic interactions [14,16]. The squareness, i.e. the ratio of the remanent magnetization (Mr) to Ms (Mr/Ms), is an important characteristic parameter for applications for ferro/ferri-magnetic materials. The calculated values of Mr/Ms are listed in Table 3. It is clear that the trend of Mr/Ms values slowly increases against x which may attribute to variation of K, Hc and Ms [14]. Basically, Ms is affected by the porosity P and crystallite size R [14]. Fig. 14(a) shows the relation between Ms and P. It is displayed that Ms decreases as P increases which confirms the dependence of Ms on P [14]. The dependence of Ms on R is seen in Fig. 14(b). It is seen that Ms increases with R and this is reasonable at which the spin canting angle decreases with increasing R [14,16].
3.5. Magnetic hysteresis loops 4. Conclusion RT magnetic hysteresis loops of M-type hexagonal BaTixFe12 4/ 3xO19 nanoferrites are depicted in Fig. 12. It is depicted that the curves have a wide hysteretic behavior (high coercivity Hc) which is characteristic of hard magnetic materials [1,4–6,25]. Fig. 13 displays the variation of deduced saturation magnetization (Ms) against x. It is displayed that Ms decreases against x, whereas the recorded values of coercivity Hc (Table 3) changes
M-type hexagonal BaTixFe12 (4/3)xO19 nanoparticles, 0.0 rx r1, were prepared by co-precipitation route and annealing at 1200 °C for 20 h. The results revealed that all samples have single M-type hexagonal phase structure (magnetoplumbite structure). The average particle size ranged 42.35–61.30 nm and is a little higher than the crystallite size R where they showed decrease with Ti4 þ
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content x. Seven absorption bands ν1, ν2, ν3, ν4, νA, νB and νT were observed in the IR spectra and assigned to their corresponding sites and bonds. They pointed to the existence of the ions Fe2 þ and Fe4 þ in the crystal sublattices. The lattice constants, density, porosity (P), strain (ε), specific surface area, crystallite size (R), IR absorption band positions, threshold frequency, Debye temperature, saturation magnetization (Ms), remanent magnetization, coercivity, squareness and magnetic moment were affected by Ti4 þ ion concentration x. VSM curves displayed wide hysteretic behaviors with higher coercivity which is characteristic of the typical hard magnetic materials, and this is a very desirable characteristic for recording media. Ms and ε proved dependence on P and R. The net weight loss of the samples heated from room temperature up to 1000 °C led in the range of 0.00418–0.01834% weight, where the maximum weight loss occurred before heating temperature 500 °C. Heating the samples above 1000 °C did not show a noticeable weight loss, which most likely may due to the onset of BaTixFe12 4/3xO19 nano-ferrites phase.
Acknowledgment The authors are grateful to the council of Tanta University for supporting the current research project under the code number 01-13-05.
References [1] S.P. Gairola, V. Verma, A. Singh, L.P. Purohit, R.K. Kotnala, Solid State Commun. 150 (2010) 147. [2] A. Goldman, Modern Ferrite Technology, Marcel Dekker Inc., New York, 1993. [3] Y. Liu, M.G.B. Drew, Y. Liu, J. Magn. Magn. Mater. 323 (2011) 945. [4] S.M. El-Sayed, T.M. Meaz, M.A. Amer, H.A. ElShersaby, Physica B 426 (2013) 137. [5] J. Dho, E.K. Lee, J.Y. Park, N.H. Hur, J. Magn. Magn. Mater. 285 (2005) 164. [6] S. Ounnunkad, P. Winotai, J. Magn. Magn. Mater. 301 (2006) 292. [7] M.A. Amer, T.M. Meaz, S.S. Attalah, A.I. Ghoneim, J. Magn. Magn. Mater. 363 (2014) 60. [8] B.D. Cullity, Elements of X-ray Differaction, second edition,. Addison-wesley puplishing company, Inc., USA, 1978.
[9] S.A. Safaan, A.M. Abo El Ata, M.S. El Messeery, J. Magn. Magn. Mater. 302 (2006) 362. [10] Y. Liu, M.G.B. Drew, J. p. Wang, M. Zhang, Y. Liu, J. Magn. Magn. Mater. 322 (2010) 366. [11] C. Wang, X. Qi, L. Li, Ji Zhou, X. Wang, Z. Yue, Mater. Sci. Eng. B 99 (2003) 270. [12] G. Dixit, J.P. Singh, R.C. Srivastava, H.M. Agrawal, J. Magn. Magn. Mater. 324 (2012) 479. [13] P.P. Hankare, R.P. Patil, U.B. Sankpal, S.D. Jadhav, I.S. Mulla, K.M. Jadhav, B. K. Chougule, J. Magn. Magn. Mater. 321 (2009) 3270. [14] M.A. Amer, T.M. Meaz, A.G. Mostafa, H.F. El-Ghazally, Mater. Sci. Semicond. Process. 32 (2015) 68. [15] E.C. Subfarao, J. Am. Ceram. Soc. 43 (1960) 119. [16] D.H. Bobade, S.M. Rathod, M.L. Mane, Physica B 407 (2012) 3700. [17] E. Ranjith Kumar, R. Jayaprakash, Sanjay Kumar, J. Magn. Magn. Mater. 351 (2014) 70. [18] Ping Hu, Hai-bo Yang, De-an Pan, Hua Wang, Jian-jun Tian, Shen-gen Zhang, Xin-feng Wang, Alex A. Volinsky, J. Magn. Magn. Mater. 322 (2010) 173. [19] M. Ahmad, I. Ali, R. Grossinger, M. Kriegisch, F. Kubel, M.U. Rana, J. Alloy. Compd. 579 (2013) 57. [20] M. Ahmad, R. Grössinger, M. Kriegisch, F. Kubel, M.U. Rana, J. Magn. Magn. Mater. 332 (2013) 137. [21] S.M. Patange, S.E. Shirsath, K.S. Lohar, S.G. Algude, S.R. Kamble, N. Kulkarni, D. R. Mane, K.M. Jadhav, J. Magn. Magn. Mater. 325 (2013) 107. [22] S.M. Patange, Sagar E. Shirsath, S.P. Jadhav, V.S. Hogade, S.R. Kamble, K. M. Jadhav, J. Mol. Struct. 1038 (2013) 40. [23] S.A. Mazen, S.F. Mansour, E. Dhahri, H.M. Zaki, T.A. Elmosalami, J. Alloy. Compd. 470 (2009) 294. [24] M.A. Amer, T.M. Meaz, A.G. Mostafa, M. El-Kastawy, A.I. Ghoneim, Ceram. Int. 40 (2014) 241. [25] G.B. Teh, S. Nagalingam, D.A. Jefferson, Mater. Chem. Phys. 101 (2007) 158. [26] P.P. Hankare, V.T. Vader, N.M. Patil, S.D. Jadhav, U.B. Sankpal, M.R. Kadam, B. K. Chougule, N.S. Gajbhiye, Mater. Chem. Phys. 113 (2009) 233. [27] M. Sivakumar, A. Towata, K. Yasui, T. Tuziuti, T. Kozuka, Y. Iida, M.M. Maiorov, E. Blums, D. Bhattacharya, N. Sivakumar, M. Ashok, Ultrason. Sonochem. 19 (2012) 652. [28] R. Gimenes, M.R. Baldissera, M.R.A. da Silva, C.A. DA Silveira, D.A.W. Soares, L. A. Perazolli, M.R. da Silva, M.A. Zaghete, Ceram. Int. 38 (2012) 741. [29] R.A. Khan, S. Mir, A.M. Khan, B. Ismail, Abdur Rahman Khan, Ceram. Int. 40 (2014) 11205. [30] F. Song, X. Shen, M. Liu, Jun Xiang, Solid State Sci. 12 (2010) 1603. [31] J. Bursik, Ivo Drbohlav, Z. Frait, K. Knizek, R. Kuzel, K. Kouril, J. Solid State Chem. 184 (2011) 3085. [32] I. Ali, M.U. Islam, M.S. Awan, M. Ahmad, M.N. Ashiq, S. Naseem, J. Alloy. Compd. 550 (2013) 564. [33] M.A. Gabal, R.S. Al-luhaibi, Y.M. Al Angari, J. Hazard. Mater. 246–247 (2013) 227. [34] S. Kracunovska, J. Töpfer, J. Magn. Magn. Mater. 320 (2008) 1370. [35] V. Kumar, A. Rana, M.S. Yadav, R.P. Pant, J. Magn. Magn. Mater. 320 (2008) 1729.