- Email: [email protected]
Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route
Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route Javed Rehman a, Muhammad Azhar Khan a,n, Altaf Hussain a, F. Iqbal a, Imran Shakir b, Ghulam Murtaza c, Majid Niaz Akhtar d, Gulfam Nasar e, Muhammad Farooq Warsi e,n a
Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan Deanship of Scientific Research, College of Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia Centre for Advanced Studies in Physics, Government College University, Lahore 54000, Pakistan d Department of Physics, COMSATS Institute of Information Technology, Lahore 54000, Pakistan e Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan b c
art ic l e i nf o
a b s t r a c t
Article history: Received 3 February 2016 Received in revised form 27 February 2016 Accepted 28 February 2016
Terbium (Tb) doped X-type hexagonal nano-ferrites Sr2NiCoTbxFe28 xO46 (x ¼0.00, 0.05, 0.1, 0.15, 0.2) were synthesized via micro-emulsion route. Single phase X-type hexagonal structure was confirmed by X-ray diffraction (XRD) analysis. The crystallite size of the samples was found in the range of 15–25 nm. The bulk density and X-ray density were enhanced while porosity was reduced with the increased Tb3 þ contents. The development of hexagonal phase was investigated by thermogravimetric analysis. The fourier-transform infrared (FTIR) spectra revealed the formation of spectral bands (metal-oxygen stretching vibration) which confirmed the hexagonal ferrites. The dielectric constant has high value at low frequency and decreased with increased frequency. The dielectric loss is appreciably decreased by the Tb3 þ incorporation and resonance phenomenon occurred beyond 1.7 109 Hz. The saturation magnetization (76–54 emu/g) and remanance (27–21 emu/g) decreased while coercivity increased (610– 747 Oe) by Tb3 þ -incorporation in Sr2NiCoTbxFe28 xO46 ferrite. The values of squareness ratio (0.35–0.39) indicated that Tb-doped samples are single domain while un-doped material is multi domains. These synthesized nano-sized hexagonal ferrites have potential applications in high frequency and recording media devices. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Dielectric properties Nano-ferrites XRD FTIR Saturation magnetization Coercivity
1. Introduction Hexagonal ferrites were discovered at Philips laboratory in 1952. H. P. J. Wijn and J. Smit discussed the properties of hexagonal ferrites in their book entitled “Ferrites”. The structure of hexagonal ferrite is much more complex as compared to spinel and other ferrites. Their structure can be described with unique c-axis of hexagonal structure. In hexagonal ferrites, direction of magnetization cannot be altered easily to another axis [1]. Hexagonal ferrites are categorized into six categories on the basis of their crystal structure and chemical formula. These classes are M-type, U-type, W-type, X-type, Y-type, and Z-type. M-type hexagonal ferrites have been used as permanent magnets, high density magnetic recording media and millimeter wave devices. The n
Corresponding authors. E-mail addresses: [email protected] (M.A. Khan), [email protected] (M.F. Warsi).
structure of W-type (BaFe18O27) hexagonal ferrite is similar to M-type, there are two S blocks below and above R block in W-type hexagonal ferrite instead of one as in M-type hexagonal ferrite [2]. The magnetic, electrical and dielectric parameters of W-type ferrites can be optimized by judicial choice of other metal cations [3]. W-type hexagonal ferrites exhibit the inherent soft magnetic behavior. This soft magnetic character is due to high sintering temperature during their formation, which yields the large grain sized material. Due to the soft magnetic character, W-type hexagonal ferrites are used as micro wave absorbers [4]. X-type hexagonal ferrites were formed at very high temperature (1350 °C) [5,6]. X-type ferrites have larger Curie temperature (Tc) and roomtemperature saturation magnetization (MS) as compared to M-type and W-type hexagonal ferrites. X-type hexagonal ferrites (Sr2M2Fe28 xO46) are more stable as compared to W-type ferrites. These properties of X-type hexagonal ferrites make them useful for advanced technological applications [7]. The X-type hexagonal ferrites have potential applications for fabricating the microwave devices which are required to operate at GHz frequency range [8].
http://dx.doi.org/10.1016/j.ceramint.2016.02.171 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Leccabue et al. [9] studied the La3 þ -doped Ba-X hexagonal ferrites. They found that the saturation magnetization increased and the Curie temperature was decreased with the doping of La3 þ cations. Sadiq et al. [6] recently worked on neodymium (Nd) and cobalt (Co) co-doped SrNi-X hexagonal ferrites. The magnetic and microwave absorption properties were found to improve with the doping of Nd–Co contents. Samarium (Sm) and manganese (Mn) co-doped SrNi-X hexagonal ferrites were also investigated by the same research group [10]. These ferrites were found suitable in the fabrication of microwave devices. They also reported the gadolinium (Gd) and cadmium (Cd) co-doped SrNi-X hexagonal ferrites [11]. The magnetic properties of these ferrites were enhanced with the doping of Gd-Cd contents and were found applicable in super high frequency devices. The effect of cesium (Ce) and zinc (Zn) codoping on SrNi-X hexagonal ferrites properties has also been reported in the literature. The magnetic and electrical properties were optimized with the doping of Ce–Zn contents [12]. The aim of the present research work is to synthesize the Sr2NiCoTbxFe28 xO46 (x¼ 0, 0.05, 0.10, 0.15 and 0.20) X-type hexagonal ferrites by wet chemical route (micro-emulsion technique) with smaller crystallite size ( r50 nm) and to unfold the impact of Tb3 þ (a rare earth metal cation) on the structural, spectral, dielectric and magnetic behavior of these ferrites.
2. Experimental details Micro-emulsion method was used to prepare the X-type hexagonal ferrites Sr2NiCoTbxFe28 xO46 (x ¼0, 0.05, 0.10, 0.15 and 0.20). Aqueous solutions of following metal salts were prepared in deionised water. Sr(No3)2, NiCl2, (CH3 COO)2 Co 4H2O, TbCl3 and. Required volumes of these freshly prepared aqueous solutions were mixed and then stirred at 60 °C. The pH of all the reaction mixtures was initially ∼3. Using freshly prepared aqueous (5 M) ammonia solution, the pH was raised from acidic medium to basic medium. The pH was maintained at ∼11 for all the reaction mixtures. After that the resultant mixtures were stirred for 5 h continuously at room temperature. To reduce the pH, all the precipitates were washed by deionized water several times. The precipitates were then dried in different beakers in oven at ∼100 °C. The dried precipitates were grinded with the help of mortar and pestle. The mortar and pestle was washed and dried after each composition to avoid any contamination. Using controlled muffle furnace Vulcan A-550, the dried grinded samples were annealed. The annealing temperature was maintained at 1300 °C. The annealing time was 7 h continuously. All the five annealed samples were packed in air tight glass vials and stored for further characterization.
Fig. 1. TGA, DTA and DSC curves for Sr2NiCoTb0.1Fe27.9O46 X-type ferrite.
peaks are at temperature 70 °C, 172 °C and 262 °C due to the crystallization and decomposition of the sample [15]. The two endothermic peaks are detected at 600 °C (due to the formation of hexagonal phase) [16] and at 1035 °C (due to the development of X-type hexagonal structure) [17]. DSC curve give one exothermic and one endothermic peak at a temperature of 260 °C and 1250 °C respectively. The exothermic peak appeared due to the removal of organic compounds, dehydration of water molecules, decomposition of hydroxides and nitrates [18]. The endothermic peak is due to the formation of X-type hexagonal structure [19]. 3.2. Structural properties The structural properties of Tb3 þ -doped X-type hexagonal ferrites (Sr2NiCoTbxFe28 xO46) were investigated by XRD patterns of all compositions that were annealed for 7 h at 1300 °C. (Fig. 2). The single hexagonal phase of the prepared sample was matched with ICSD # 024574. This confirmed that the samples have X-type hexagonal structure [20]. The cell volume was calculated by the formula:
V = a2c sin 120°
(1)
The unit cell volume varies with composition and this behavior is shown in the Fig. 3. It first increases and then decreased. The X-ray density was calculated by the formula:
Dx = 3 M /NV
(2)
It is shown in the Table 1 that X-ray density increased with Tb-
x = 0.20
3. Results and discussion
Thermal properties of Sr2NiCoTbxFe28 xO46 nano-ferrites were investigated by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). TGA, DSC and DTA curves are shown in Fig. 1. TGA curve is divided into three parts. The first weight loss is 4% occurred at a temperature up to 75 °C. The 2nd weight loss is 16%. The 2nd weight loss happens at a temperature 325 °C due to the evaporation of water molecules trapped among the pores of particles [13]. The final weight loss is 17% at temperature ∼1100 °C. The peak observed at a temperature 1100 °C is due to the formation of hexagonal phase [14]. DTA curve shows three exothermic and two endothermic peaks at different temperatures. The exothermic
x = 0.15
Intensity (a.u)
3.1. Thermal properties
x = 0.10
x = 0.05
1112 1016 110 10
20
30
0129 0219 2113 40
033
1229
50
60
0330
x = 0.00 70
80
2 theta (degrees) Fig. 2. XRD patterns of Sr2NiCoTbxFe28 xO46 (x ¼0, 0.05, 0.10, 0.15 and 0.20) X-type ferrites.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Fig. 3. The variation of cell volume with composition for Sr2NiCoTbxFe28 xO46 X-type ferrites.
contents [15]. The bulk density was determined by the relation:
D = m/Πr 2h
(3)
It is also shown in the Table 1, that the bulk density increased with increased Tb3 þ contents [21]. The porosity was determined given by the following relation:
P = 1 – D / Dx
Fig. 4. Variation of crystalline size with composition for Sr2NiCoTbxFe28 xO46 X-type ferrites.
(4)
It is clear from the Table 1 that porosity first decreased and then increased. The decreasing effect is caused by the micro strains. These micro strains yield the compressive stress in the lattice and therefore porosity decreases. The increasing effect is due the combining of the small vacancies to form large vacancies [6]. The crystallite size was calculated by the relation:
S = kλ / β Cos θ
(5)
In Eq. (5) ʎ is the wave length, k is constant and is equal to 0.94,
β is the full width at half maxima. The crystallite size was found in
the range 15–25 nm. The effect of Tb-contents on variation of crystallite size is depicted in Fig. 4. This variation is due the various sites of the unit cell [22]. The increase in the crystalline size is due the fact that terbium (Tb) goes to the octahedral site rather than tetrahedral site, however as we increased the Tb3 þ -contents, the crystallite size was decreased. This decrease in crystallite size is due to the compressive stress by Tb3 þ -ions [6].
Fig. 5. FTIR spectra for Sr2NiCoTbxFe28 xO46 (x¼ 0.1, 0.15, 0.2) X-type hexagonal ferrites.
3.4. Dielectric properties
3.3. Spectral properties FTIR spectra of three selected compositions (x ¼0.1, 0.15, 0.20) of Sr2NiCoTbxFe28 xO46 ferrites are shown in the Fig. 5. FTIR spectroscopy explained the chemical and structural changes of the material during combustion and annealing process [23]. The sharp peaks are present at 668 cm 1, 1339 cm 1 and 1362 cm 1. The band at 668 cm 1 arises due to the metal-oxygen stretching vibration of hexagonal ferrites [24] and the bands at 1339 cm 1 and 1362 cm 1 are attributed to presence of trapped nitrates [25].
The materials with high dielectric constant (ɛ‘) are important in the manufacturing of high value capacitors. The relative speed of an electromagnetic signal which move in the material is measured by dielectric constant [26]. The dielectric parameters for all samples were measured at room temperature in the range of 1 MHz to 3 GHz. The effect of Tb3 þ contents and frequency on dielectric constant is shown in Fig. 6. The Fig. 6 shows that ɛ‘ decreased as frequency was increased. The resonance peaks in the Figure
Table 1 Lattice parameters, cell volume, X-ry density, bulk density, crystallite size and porosity of Sr2NiCoTbxFe28 xO46 (x¼ 0.00, 0.05, 0.1, 0.15, 0.2) hexagonal ferrites. Parameters
X ¼ 0.0
X ¼ 0.05
X ¼ 0.10
X ¼ 0.15
X ¼0.20
Lattice constant a (Å) Lattice constant c (Å) c/a ratio Unit cell volume V (Å3) X-ray density Dx (g/cm3) Bulk density D (g/cm3) Porosity P Crystalline size S (nm)
5.283 83.720 15.847 2022.757 6.384 3.236 0.494 22.66
5.286 83.724 15.839 2025.919 6.386 3.240 0.493 24.78
5.287 83.726 15.836 2026.734 6.397 3.334 0.479 25.568
5.285 83.725 15.842 2025.177 6.414 3.338 0.480 18.488
5.282 83.726 15.851 2022.902 6.434 3.332 0.483 15.098
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
Fig. 8. Variation of Tangent loss with frequency of Sr2NiCoTbxFe28 xO46 X-type ferrites. Fig. 6. The variation of dielectric constant vs frequency of Sr2NiCoTbxFe28 xO46 X-type ferrites.
appeared due to the fact that when jumping frequency of electrons between Fe3 þ and Fe2 þ ions becomes equal to the frequency of the applied ac field [27]. Dielectric constant (ɛ‘) was determined by the formula:
tangent loss decreases by increasing frequency. At octahedral sites the hoping of electrons between Fe2 þ and Fe3 þ ions creates conduction mechanism [30]. The measure of the amount of passage of electrical current in a material is called electrical conductivity. Ac conductivity was determined by the formula:
ε′ = Cd/Aεo
σac =σ1 (T )+σ 2 (ω, T )
(6)
(9)
In Eq. (6), A is the cross-sectional area of the pellet, C is the capacitance of pellet, εo is the permittivity of free space and d is thickness of the pellet. Dielectric loss factor is given by the equation:
In Eq. (9) the first part s1 (T) is DC conductivity and the second part s2(ω,T) is frequency and temperature dependent. This part indicates the dielectric relaxation caused by bound or localized charge carriers [31]. This term can also be written as:
ϵ ′′ = ϵ′/ tan (δ )
σ 2 (ω, T ) = B (T ) ωn (T )
(7)
The dielectric loss factor (ε'') curves for all compositions of Sr2NiCoTbxFe28 xO46 nano-ferrites are shown in Fig. 7. The Fig. 7 shows that by increasing frequency the value of dielectric loss factor also found to decrease. The peaks in the Fig. 7 arises due the intrinsic electric dipole polarization and interfacial polarization [28]. Tangent loss is the ratio between loss or resistive current and charging current in the sample and is given by the equation [29]:
tan δ = ϵ″/ϵ′
(8)
The value of tangent loss is affected by several factors, such as structural homogeneity, sintering temperature and chemical composition of the materials [15]. Maxwell–Wagner theory explains that there is inverse relation between tangent loss and dielectric constant (ɛ‘) with frequency [26]. The Fig. 8 shows that
Fig. 7. Variation of dielectric loss factor with frequency of Sr2NiCoTbxFe28 xO46 X-type ferrites.
(10)
Ac conductivity of the prepared nano-ferrites could be calculated by the relation:
σac = ω ∈o ϵ″ = ω ∈o ϵ′ tan δ = 2πf ∈o ϵ′ tan δ
(11)
This equation shows that by increasing frequency the ac conductivity increases [32]. The Fig. 9 shows that ac conductivity was increased with the increased frequency. The heterogeneous model of polycrystalline structure states that polycrystalline materials are composed of conducting grains. These grains are detached by highly resistive layers (grain boundaries). At lower frequency, the resistance between the grains is large and thus ac conductivity has low value, however at higher frequency, the ac conductivity
Fig. 9. Log (ω) vs log (sac) for Sr2NiCoTbxFe28 xO46 (x¼ 0.0, 0.5, 0.10, 0.15, 0.20) X-type hexagonal ferrites.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
5
Fig. 10. Real part of electric modulus (M’) vs Frequency of Sr2NiCoTbxFe28 xO46 (x¼ 0.0, 0.5, 0.10, 0.15, 0.20) X-type hexagonal ferrites.
Fig. 12. M-H loop of Sr2NiCoTbxFe28 xO46 (x ¼ 0.00, 0.05, 0.1, 0.15, 0.2) hexagonal ferrites.
increases due to reduced resistive layers among grains. [26]. The variation of real part of electric modulus (M’) with frequency is shown in Fig. 10. At low frequency region the value of M’ is low. The value of M’ increases by increasing frequency and finally at higher frequency M’ reaches a maximum constant value for all samples [33]. The variation of imaginary part of electric modulus (M”) with frequency for all compositions of X-type hexagonal ferrites (Sr2NiCoTbxFe28 xO46) is shown in Fig. 11. The peaks in the Figure describe the conductivity relaxation. This pattern explain charge transport processes like conduction relaxation and electrical transport as a function of frequency [34]. Imaginary part of electric modulus expresses the loss of energy [35]. Cole-Cole plots are used to separate the grain and grain boundary contributions [36]. These plots unfold information about large volume of grain boundaries [37]. The density of the grain boundaries increases when Tb is added to the samples and thus the resistance of the grain boundaries also increases [38].
Table 2 Estimated saturation magnetization Ms, remanace magnetization Mr and squareness ratio of Tb doped SrNiCo-X hexagonal ferrites.
3.5. Magnetic properties Fig. 12 shows the M–H loops of Sr2NiCoTbxFe28 xO46 (x¼0.00, 0.05, 0.1, 0.15, 0.2) hexagonal nano-ferrites. The decrease in saturation magnetization (Ms) and remanance magnetization (Mr) in the range 76–54 emu/g and 27–21 emu/g respectively was found
Sub-lattice
Coordination
Block
Number of ions
Spin
6c1v 3av1 18hVI 6cvI 6cIV 3bv1
Tetrahedral Octahedral Octahedral Octahedral Tetrahedral Octahedral
S S S–T T T T
2 1 6 2 2 1
Down Up Up Down Down Up
with the increased Tb3 þ -contents. The coercivity was found to increase from 610 to 747 Oe with the increase of Tb3 þ -contents. The variations in magnetic properties may be due to the cationic distribution in different sites of S and T blocks [39]. The six different sites 6c1v, 3av1, 18hVI, 6cvI, 6cIV, 3bv1 are listed in Table 2 [2]. The variation in Ms and Mr can be explained on the basis of super exchange interaction between tetrahedral 6c1v and octahedral 3av1 sites of the S-blocks [24,40]. The replacing of iron ions with rare earth metal ions in Sr2NiCoTbxFe28 xO46 hexagonal ferrites resulted in diluting the magnetic interactions. As the iron is replaced by Tb3 þ cations, the super exchange interaction between 3av1 and 6c1v sites is reduced. This is due to the different magnetic moment of iron ions and rare earth metal (Tb3 þ ) cations (magnetic moment of iron 5μB and magnetic moment of rare earth metal 0) [40]. Therefore, the net magnetic moment of the Tbdoped SrCoNi-X type ferrites was reduced (Table 3). The coercivity (Hc) was increased with the increased Tb-contents. The values of Hc were found in the range 610–747. The enhanced coercivity is explained on the basis of c/a ratio. The c/a ratio of the prepared nano-ferrites lies in the range 15.851-15.836. This factor reduced the demagnetization factor that resulted the Table 3 Ms, Mr, Hc and squarness ratio of Sr2NiCoTbxFe28 xO46 (x ¼0.00, 0.05, 0.1, 0.15, 0.2) hexagonal ferrites.
̋
Fig. 11. Variation of imaginary part of electric modulus (M) with frequency of Sr2NiCoTbxFe28 xO46 (x¼ 0.0, 0.5, 0.10, 0.15, 0.20) X-type hexagonal ferrites.
S.no
Ms (emu/g)
Mr (emu/g)
Hc (Oe)
Squarness ratio
1 2 3 4 5
76.244 70.708 65.172 62.404 54.100
27.400 25.910 24.440 23.705 21.500
610.17 644.385 678.600 695.708 747.03
0.359 0.366 0.375 0.380 0.397
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
6
optimization of coercivity [40,41]. The coercivity (Hc) and saturation magnetization (Ms) are related with each other by the following relation:
Hc =K1 /μo Ms
(12)
The values of coercivity Hc is greater than half of the ramanance magnetization Mr i.e (Hc 4Mr/2). The materials which have greater coercivity than half of the remanance magnetization Mr can be used for high frequency applications [40,42]. The squarness ratio was calculated from Ms and Mr values and found in the range of 0.359–0.397. All compositions exhibited the squarness values smaller than the typical value 1 for single domain isolated ferromagnetic particle [40]. The values of squarness ratio decreased with increase of doping (Tb) concentration which shows that the particles may reside as single domain. The pure SrCoNi-X ferrites have a small value of squarness ratio that shows that particles are completely randomly oriented and exist in multi domains [40].
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
4. Conclusions TGA curve revealed that the maximum weight loss occurred at 325 °C. The hexagonal phase was developed at 1100 °C. XRD patterns reveal that the prepared nano-ferrites have hexagonal structure. The crystalline size was increased from 22 nm to 25 nm when doping concentration of Tb was increased for x ¼0.00 to x ¼0.10 and then decreased to 15 nm as Tb-concentration was increased from x¼ 0.15 to 0.20. The FTIR spectra of nano-ferrites in the range 1362–668 cm 1 also confirmed the hexagonal phase of the prepared samples. The value of dielectric constant was 12.5 at low at frequency and abruptly decreased to 6.5 at high frequency. The incorporation of terbium lowers the saturation magnetization and remanance from 76 to 54 emu/g and 27 to 21 emu/g respectively. The coercivity was increased from 610 to 747 Oe with the increased Tb-concentration. The variations in magnetic properties may be attributed to the redistribution of cations on different sites of S and T blocks. The synthesized X-type nano-ferrites are useful in the fabrication of high frequency devices and recording media applications.
Acknowledgment One of the authors (I. Shakir) is highly thankful to the Deanship of Scientific Research, King Saud University, Riyadh for Prolific Research Group Project no. PRG-1436-25.
[17]
[18]
[19]
[20] [21]
[22]
[23]
[24]
[25] [26]
[27]
[28] [29]
[30]
References [31] [1] R.C. Pullar, Hexagonal ferrites: a review of the synthesis, properties and applications of hexaferrite ceramics, Prog. Mater. Sci. 57 (2012) 1191–1334. [2] G. Albanese, Recent advances in hexagonal ferrites by the use of nuclear spectroscopic methods, Le Journal De Physique Colloques 38 (1977), C1-85C81-C94. [3] F. Aen, S.B. Niazi, M. Islam, M. Ahmad, M. Rana, Effect of holmium on the magnetic and electrical properties of barium based W-type hexagonal ferrites, Ceram. Int. 37 (2011) 1725–1729. [4] G.M. Rai, M. Rana, Dielectric and magnetic behavior of BaCd2 xSrxFe16O27 w-type hexagonal ferrites, J. Alloy. Compd. 509 (2011) 4793–4796. [5] G. Ben-Xi, L. Huai-Xian, D. You-Wei, Magnetic properties and Mössbauer spectra of X type hexagonal ferrites, J. Magn. Magn. Mater. 31 (1983) 803–804. [6] I. Sadiq, I. Khan, E.V. Rebrov, M.N. Ashiq, S. Naseem, M. Rana, Structural, infrared, magnetic and microwave absorption properties of rare earth doped X-type hexagonal nanoferrites, J. Alloy. Compd. 570 (2013) 7–13. [7] B. Gu, Magnetic properties of X‐type Ba2Me2Fe28O46 (Me¼ Fe, Co, and Mn) hexagonal ferrites, J. Appl. Phys. 71 (1992) 5103–5106. [8] Z. Haijun, L. Zhichao, Y. Xi, Z. Liangying, W. Mingzhong, Dielectric and
[32] [33]
[34]
[35] [36]
[37]
magnetic properties of ZnCo-substituted X hexaferrites prepared by citrate sol–gel process, Mater. Res. Bull. 38 (2003) 363–372. F. Leccabue, R. Panizzieri, S. Garcia, N. Suarez, J. Sanchez, O. Ares, X.R. Hua, Magnetic and mössbauer study of rare-earth-substituted M-, W-and X-type hexagonal ferrites, J. Mater. Sci. 25 (1990) 2765–2770. I. Sadiq, I. Khan, E.V. Rebrov, M. Naeem Ashiq, S. Naseem, I. Shakir, M.U. Rana, Influence of Sm–Mn substitution on structural, dielectric and electrical properties of X-type hexagonal nanoferrites, J. Chem. Soc. Pak. 37 (2015) 33–38. I. Sadiq, S. Naseem, M. Rana, M.N. Ashiq, I. Ali, Temperature dependent magnetic and microwave absorption properties of doubly substituted nanosized material, J. Magn. Magn. Mater. 385 (2015) 236–242. I. Sadiq, I. Ali, E. Rebrov, S. Naseem, M.N. Ashiq, M. Rana, Nanosized Ce–Zn substituted microwave absorber material for X-band applications, J. Magn. Magn. Mater. 370 (2014) 25–31. S.Y. An, I.-B. Shim, C.S. Kim, Mössbauer and magnetic properties of Co–Ti substituted barium hexaferrite nanoparticles, J. Appl. Phys. 91 (2002) 8465–8467. K.K. Mallick, P. Shepherd, R.J. Green, Dielectric properties of M-type barium hexaferrite prepared by co-precipitation, J. Eur. Ceram. Soc. 27 (2007) 2045–2052. I. Sadiq, I. Ali, E.V. Rebrov, S. Naseem, M.N. Ashiq, M. Rana, Influence of Nd–Co substitution on structural, electrical, and dielectric properties of X-type hexagonal nanoferrites, J. Mater. Eng. Perform. 23 (2014) 622–627. H.-I. Hsiang, R.-Q. Yao, Hexagonal ferrite powder synthesis using chemical coprecipitation, Mater. Chem. Phys. 104 (2007) 1–4. T. Strukturne, N.I.M.L. Prahov, Structural, thermal and magnetic properties of barium-ferrite powders substituted with Mn, Cu or Co and X (X ¼ Sr and Ni) prepared by the sol–gel method, Mater. Technol. 46 (2012) 305–310. Z. Haijun, L. Zhichao, M. Chenliang, Y. Xi, Z. Liangying, W. Mingzhong, Preparation and microwave properties of Co-and Ti-doped barium ferrite by citrate sol–gel process, Mater. Chem. Phys. 80 (2003) 129–134. S. Kulkarni, J. Shrotri, C. Deshpande, S. Date, Synthesis of chemically coprecipitated hexagonal strontium-ferrite and its characterization, J. Mater. Sci. 24 (1989) 3739–3744. M. Azim, S. Atiq, S. Naseem, Structural and electrical characterization of lanthanum doped strontium hexaferrites, Sci. Int. 24 (2012) 341. M. Ahmed, N. Okasha, R. Kershi, Dramatic effect of rare earth ion on the electrical and magnetic properties of W-type barium hexaferrites, Phys. B: Condens. Matter 405 (2010) 3223–3233. P.A. Kumar, J. Shrotri, S. Kulkarni, C. Deshpande, S. Date, Low temperature synthesis of Ni0.8Zn0.2Fe2O4 powder and its characterization, Mater. Lett. 27 (1996) 293–296. R. Jotania, R. Khomane, C. Chauhan, S. Menon, B. Kulkarni, Synthesis and magnetic properties of barium–calcium hexaferrite particles prepared by sol– gel and microemulsion techniques, J. Magn. Magn. Mater. 320 (2008) 1095–1101. A. Elahi, M. Ahmad, I. Ali, M. Rana, Preparation and properties of sol–gel synthesized Mg-substituted Ni2Y hexagonal ferrites, Ceram. Int. 39 (2013) 983–990. C. Chen, J. Cheng, S. Yu, L. Che, Z. Meng, Hydrothermal synthesis of perovskite bismuth ferrite crystallites, J. Cryst. Growth 291 (2006) 135–139. Z. Anwar, M.A. Khan, I. Ali, M. Asghar, M. Sher, I. Shakir, M. Sarfraz, M.F. Warsi, Investigation of dielectric behavior of new Tb3 þ doped BiFeO3 nanocrystals synthesized via micro-emuslion route, J. Ovonic Res. 10 (2014) 265–273. R. Kambale, P. Shaikh, C. Bhosale, K. Rajpure, Y. Kolekar, Dielectric properties and complex impedance spectroscopy studies of mixed Ni–Co ferrites, Smart Mater. Struct. 18 (2009) 085014. Z. Haijun, Y. Xi, Z. Liangying, The preparation and microwave properties of Ba2ZnxCo2 xFe28O46 hexaferrites, J. Magn. Magn. Mater. 241 (2002) 441–446. Iqbal Muhammad Jave d, Ashiq Muhammad Naeem, Gomez Pablo Hernandez, Effect of doping of Zr–Zn binary mixtures on structural, electrical and magnetic properties of Sr-hexa ferrite nanoparticles, J. Alloy. Compd. 478 (2009) 736–740. A.A. El Ata, M. El Nimr, D. El Kony, A. Al-Hammadi, Dielectric and magnetic permeability behavior of BaCo2 x NixFe16O27 w-type hexaferrites, J. Magn. Magn. Mater. 204 (1999) 36–44. M. El Hiti, Dielectric behavior and ac electrical conductivity of Zn-substituted Ni Mg ferrites, J. Magn. Magn. Mater. 164 (1996) 187–196. A.A. El Ata, M. Ahmed, Dielectric and AC conductivity for BaCo2 xCuxFe16O27 ferrites, J. Magn. Magn. Mater. 208 (2000) 27–36. M.A. Iqbal, I. Ali, H.M. Khan, G. Mustafa, I. Ali, Study of electrical transport properties of Eu þ 3 substituted MnZn-ferrites synthesized by co-precipitation technique, Ceram. Int. 39 (2013) 1539–1545. M.N. Ashiq, M.J. Iqbal, I.H. Gul, Structural, magnetic and dielectric properties of Zr–Cd substituted strontium hexaferrite (SrFe12O19) nanoparticles, J. Alloy. Compd. 487 (2009) 341–345. I. Gul, A. Maqsood, Structural, magnetic and electrical properties of cobalt ferrites prepared by the sol–gel route, J. Alloy. Compd. 465 (2008) 227–231. M. Chourashiya, J. Patil, S. Pawar, L. Jadhav, Studies on structural, morphological and electrical properties of Ce1 xGdxO2 (x/2), Mater. Chem. Phys. 109 (2008) 39–44. H. Rodrigues, G.P. Junior, A. Sales, P. Silva, B. Costa, P. Alcantara, S. Moreira, A. Sombra, BiFeO3 ceramic matrix with Bi2O3 or PbO added: Mössbauer, Raman and dielectric spectroscopy studies, Phys. B: Condens. Matter 406 (2011) 2532–2539.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎ [38] R. Choudhary, D.K. Pradhan, C. Tirado, G. Bonilla, R. Katiyar, Impedance characteristics of Pb (Fe2/3W1/3) O3–BiFeO3 composites, Phys. Status Solidi (b) 244 (2007) 2254–2266. [39] M.A. Gabal, W. Bayoumy, Effect of composition on structural and magnetic properties of nanocrystalline Ni0.8 xZn0.2MgxFe2O4 ferrite, Polyhedron 29 (2010) 2569–2573. [40] I. Ali, M. Islam, M.N. Ashiq, M.A. Iqbal, M. Awan, S. Naseem, Role of Tb–Mn substitution on the magnetic properties of Y-type hexaferrites, J. Alloy. Compd.
7
599 (2014) 131–138. [41] X. Liu, W. Zhong, S. Yang, Z. Yu, B. Gu, Y. Du, Influences of La3 þ substitution on the structure and magnetic properties of M-type strontium ferrites, J. Magn. Magn. Mater. 238 (2002) 207–214. [42] Y. Li, R. Liu, Z. Zhang, C. Xiong, Synthesis and characterization of nanocrystalline BaFe9.6Co0.8Ti0.8M0.8O19 particles, Mater. Chem. Phys. 64 (2000) 256–259.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
Contents lists available at ScienceDirect
Ceramics International journal homepage: www.elsevier.com/locate/ceramint
Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route Javed Rehman a, Muhammad Azhar Khan a,n, Altaf Hussain a, F. Iqbal a, Imran Shakir b, Ghulam Murtaza c, Majid Niaz Akhtar d, Gulfam Nasar e, Muhammad Farooq Warsi e,n a
Department of Physics, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan Deanship of Scientific Research, College of Engineering, King Saud University, PO Box 800, Riyadh 11421, Saudi Arabia Centre for Advanced Studies in Physics, Government College University, Lahore 54000, Pakistan d Department of Physics, COMSATS Institute of Information Technology, Lahore 54000, Pakistan e Department of Chemistry, The Islamia University of Bahawalpur, Bahawalpur 63100, Pakistan b c
art ic l e i nf o
a b s t r a c t
Article history: Received 3 February 2016 Received in revised form 27 February 2016 Accepted 28 February 2016
Terbium (Tb) doped X-type hexagonal nano-ferrites Sr2NiCoTbxFe28 xO46 (x ¼0.00, 0.05, 0.1, 0.15, 0.2) were synthesized via micro-emulsion route. Single phase X-type hexagonal structure was confirmed by X-ray diffraction (XRD) analysis. The crystallite size of the samples was found in the range of 15–25 nm. The bulk density and X-ray density were enhanced while porosity was reduced with the increased Tb3 þ contents. The development of hexagonal phase was investigated by thermogravimetric analysis. The fourier-transform infrared (FTIR) spectra revealed the formation of spectral bands (metal-oxygen stretching vibration) which confirmed the hexagonal ferrites. The dielectric constant has high value at low frequency and decreased with increased frequency. The dielectric loss is appreciably decreased by the Tb3 þ incorporation and resonance phenomenon occurred beyond 1.7 109 Hz. The saturation magnetization (76–54 emu/g) and remanance (27–21 emu/g) decreased while coercivity increased (610– 747 Oe) by Tb3 þ -incorporation in Sr2NiCoTbxFe28 xO46 ferrite. The values of squareness ratio (0.35–0.39) indicated that Tb-doped samples are single domain while un-doped material is multi domains. These synthesized nano-sized hexagonal ferrites have potential applications in high frequency and recording media devices. & 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Keywords: Dielectric properties Nano-ferrites XRD FTIR Saturation magnetization Coercivity
1. Introduction Hexagonal ferrites were discovered at Philips laboratory in 1952. H. P. J. Wijn and J. Smit discussed the properties of hexagonal ferrites in their book entitled “Ferrites”. The structure of hexagonal ferrite is much more complex as compared to spinel and other ferrites. Their structure can be described with unique c-axis of hexagonal structure. In hexagonal ferrites, direction of magnetization cannot be altered easily to another axis [1]. Hexagonal ferrites are categorized into six categories on the basis of their crystal structure and chemical formula. These classes are M-type, U-type, W-type, X-type, Y-type, and Z-type. M-type hexagonal ferrites have been used as permanent magnets, high density magnetic recording media and millimeter wave devices. The n
Corresponding authors. E-mail addresses: [email protected] (M.A. Khan), [email protected] (M.F. Warsi).
structure of W-type (BaFe18O27) hexagonal ferrite is similar to M-type, there are two S blocks below and above R block in W-type hexagonal ferrite instead of one as in M-type hexagonal ferrite [2]. The magnetic, electrical and dielectric parameters of W-type ferrites can be optimized by judicial choice of other metal cations [3]. W-type hexagonal ferrites exhibit the inherent soft magnetic behavior. This soft magnetic character is due to high sintering temperature during their formation, which yields the large grain sized material. Due to the soft magnetic character, W-type hexagonal ferrites are used as micro wave absorbers [4]. X-type hexagonal ferrites were formed at very high temperature (1350 °C) [5,6]. X-type ferrites have larger Curie temperature (Tc) and roomtemperature saturation magnetization (MS) as compared to M-type and W-type hexagonal ferrites. X-type hexagonal ferrites (Sr2M2Fe28 xO46) are more stable as compared to W-type ferrites. These properties of X-type hexagonal ferrites make them useful for advanced technological applications [7]. The X-type hexagonal ferrites have potential applications for fabricating the microwave devices which are required to operate at GHz frequency range [8].
http://dx.doi.org/10.1016/j.ceramint.2016.02.171 0272-8842/& 2016 Elsevier Ltd and Techna Group S.r.l. All rights reserved.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
2
Leccabue et al. [9] studied the La3 þ -doped Ba-X hexagonal ferrites. They found that the saturation magnetization increased and the Curie temperature was decreased with the doping of La3 þ cations. Sadiq et al. [6] recently worked on neodymium (Nd) and cobalt (Co) co-doped SrNi-X hexagonal ferrites. The magnetic and microwave absorption properties were found to improve with the doping of Nd–Co contents. Samarium (Sm) and manganese (Mn) co-doped SrNi-X hexagonal ferrites were also investigated by the same research group [10]. These ferrites were found suitable in the fabrication of microwave devices. They also reported the gadolinium (Gd) and cadmium (Cd) co-doped SrNi-X hexagonal ferrites [11]. The magnetic properties of these ferrites were enhanced with the doping of Gd-Cd contents and were found applicable in super high frequency devices. The effect of cesium (Ce) and zinc (Zn) codoping on SrNi-X hexagonal ferrites properties has also been reported in the literature. The magnetic and electrical properties were optimized with the doping of Ce–Zn contents [12]. The aim of the present research work is to synthesize the Sr2NiCoTbxFe28 xO46 (x¼ 0, 0.05, 0.10, 0.15 and 0.20) X-type hexagonal ferrites by wet chemical route (micro-emulsion technique) with smaller crystallite size ( r50 nm) and to unfold the impact of Tb3 þ (a rare earth metal cation) on the structural, spectral, dielectric and magnetic behavior of these ferrites.
2. Experimental details Micro-emulsion method was used to prepare the X-type hexagonal ferrites Sr2NiCoTbxFe28 xO46 (x ¼0, 0.05, 0.10, 0.15 and 0.20). Aqueous solutions of following metal salts were prepared in deionised water. Sr(No3)2, NiCl2, (CH3 COO)2 Co 4H2O, TbCl3 and. Required volumes of these freshly prepared aqueous solutions were mixed and then stirred at 60 °C. The pH of all the reaction mixtures was initially ∼3. Using freshly prepared aqueous (5 M) ammonia solution, the pH was raised from acidic medium to basic medium. The pH was maintained at ∼11 for all the reaction mixtures. After that the resultant mixtures were stirred for 5 h continuously at room temperature. To reduce the pH, all the precipitates were washed by deionized water several times. The precipitates were then dried in different beakers in oven at ∼100 °C. The dried precipitates were grinded with the help of mortar and pestle. The mortar and pestle was washed and dried after each composition to avoid any contamination. Using controlled muffle furnace Vulcan A-550, the dried grinded samples were annealed. The annealing temperature was maintained at 1300 °C. The annealing time was 7 h continuously. All the five annealed samples were packed in air tight glass vials and stored for further characterization.
Fig. 1. TGA, DTA and DSC curves for Sr2NiCoTb0.1Fe27.9O46 X-type ferrite.
peaks are at temperature 70 °C, 172 °C and 262 °C due to the crystallization and decomposition of the sample [15]. The two endothermic peaks are detected at 600 °C (due to the formation of hexagonal phase) [16] and at 1035 °C (due to the development of X-type hexagonal structure) [17]. DSC curve give one exothermic and one endothermic peak at a temperature of 260 °C and 1250 °C respectively. The exothermic peak appeared due to the removal of organic compounds, dehydration of water molecules, decomposition of hydroxides and nitrates [18]. The endothermic peak is due to the formation of X-type hexagonal structure [19]. 3.2. Structural properties The structural properties of Tb3 þ -doped X-type hexagonal ferrites (Sr2NiCoTbxFe28 xO46) were investigated by XRD patterns of all compositions that were annealed for 7 h at 1300 °C. (Fig. 2). The single hexagonal phase of the prepared sample was matched with ICSD # 024574. This confirmed that the samples have X-type hexagonal structure [20]. The cell volume was calculated by the formula:
V = a2c sin 120°
(1)
The unit cell volume varies with composition and this behavior is shown in the Fig. 3. It first increases and then decreased. The X-ray density was calculated by the formula:
Dx = 3 M /NV
(2)
It is shown in the Table 1 that X-ray density increased with Tb-
x = 0.20
3. Results and discussion
Thermal properties of Sr2NiCoTbxFe28 xO46 nano-ferrites were investigated by thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC) and differential thermal analysis (DTA). TGA, DSC and DTA curves are shown in Fig. 1. TGA curve is divided into three parts. The first weight loss is 4% occurred at a temperature up to 75 °C. The 2nd weight loss is 16%. The 2nd weight loss happens at a temperature 325 °C due to the evaporation of water molecules trapped among the pores of particles [13]. The final weight loss is 17% at temperature ∼1100 °C. The peak observed at a temperature 1100 °C is due to the formation of hexagonal phase [14]. DTA curve shows three exothermic and two endothermic peaks at different temperatures. The exothermic
x = 0.15
Intensity (a.u)
3.1. Thermal properties
x = 0.10
x = 0.05
1112 1016 110 10
20
30
0129 0219 2113 40
033
1229
50
60
0330
x = 0.00 70
80
2 theta (degrees) Fig. 2. XRD patterns of Sr2NiCoTbxFe28 xO46 (x ¼0, 0.05, 0.10, 0.15 and 0.20) X-type ferrites.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
3
Fig. 3. The variation of cell volume with composition for Sr2NiCoTbxFe28 xO46 X-type ferrites.
contents [15]. The bulk density was determined by the relation:
D = m/Πr 2h
(3)
It is also shown in the Table 1, that the bulk density increased with increased Tb3 þ contents [21]. The porosity was determined given by the following relation:
P = 1 – D / Dx
Fig. 4. Variation of crystalline size with composition for Sr2NiCoTbxFe28 xO46 X-type ferrites.
(4)
It is clear from the Table 1 that porosity first decreased and then increased. The decreasing effect is caused by the micro strains. These micro strains yield the compressive stress in the lattice and therefore porosity decreases. The increasing effect is due the combining of the small vacancies to form large vacancies [6]. The crystallite size was calculated by the relation:
S = kλ / β Cos θ
(5)
In Eq. (5) ʎ is the wave length, k is constant and is equal to 0.94,
β is the full width at half maxima. The crystallite size was found in
the range 15–25 nm. The effect of Tb-contents on variation of crystallite size is depicted in Fig. 4. This variation is due the various sites of the unit cell [22]. The increase in the crystalline size is due the fact that terbium (Tb) goes to the octahedral site rather than tetrahedral site, however as we increased the Tb3 þ -contents, the crystallite size was decreased. This decrease in crystallite size is due to the compressive stress by Tb3 þ -ions [6].
Fig. 5. FTIR spectra for Sr2NiCoTbxFe28 xO46 (x¼ 0.1, 0.15, 0.2) X-type hexagonal ferrites.
3.4. Dielectric properties
3.3. Spectral properties FTIR spectra of three selected compositions (x ¼0.1, 0.15, 0.20) of Sr2NiCoTbxFe28 xO46 ferrites are shown in the Fig. 5. FTIR spectroscopy explained the chemical and structural changes of the material during combustion and annealing process [23]. The sharp peaks are present at 668 cm 1, 1339 cm 1 and 1362 cm 1. The band at 668 cm 1 arises due to the metal-oxygen stretching vibration of hexagonal ferrites [24] and the bands at 1339 cm 1 and 1362 cm 1 are attributed to presence of trapped nitrates [25].
The materials with high dielectric constant (ɛ‘) are important in the manufacturing of high value capacitors. The relative speed of an electromagnetic signal which move in the material is measured by dielectric constant [26]. The dielectric parameters for all samples were measured at room temperature in the range of 1 MHz to 3 GHz. The effect of Tb3 þ contents and frequency on dielectric constant is shown in Fig. 6. The Fig. 6 shows that ɛ‘ decreased as frequency was increased. The resonance peaks in the Figure
Table 1 Lattice parameters, cell volume, X-ry density, bulk density, crystallite size and porosity of Sr2NiCoTbxFe28 xO46 (x¼ 0.00, 0.05, 0.1, 0.15, 0.2) hexagonal ferrites. Parameters
X ¼ 0.0
X ¼ 0.05
X ¼ 0.10
X ¼ 0.15
X ¼0.20
Lattice constant a (Å) Lattice constant c (Å) c/a ratio Unit cell volume V (Å3) X-ray density Dx (g/cm3) Bulk density D (g/cm3) Porosity P Crystalline size S (nm)
5.283 83.720 15.847 2022.757 6.384 3.236 0.494 22.66
5.286 83.724 15.839 2025.919 6.386 3.240 0.493 24.78
5.287 83.726 15.836 2026.734 6.397 3.334 0.479 25.568
5.285 83.725 15.842 2025.177 6.414 3.338 0.480 18.488
5.282 83.726 15.851 2022.902 6.434 3.332 0.483 15.098
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
4
Fig. 8. Variation of Tangent loss with frequency of Sr2NiCoTbxFe28 xO46 X-type ferrites. Fig. 6. The variation of dielectric constant vs frequency of Sr2NiCoTbxFe28 xO46 X-type ferrites.
appeared due to the fact that when jumping frequency of electrons between Fe3 þ and Fe2 þ ions becomes equal to the frequency of the applied ac field [27]. Dielectric constant (ɛ‘) was determined by the formula:
tangent loss decreases by increasing frequency. At octahedral sites the hoping of electrons between Fe2 þ and Fe3 þ ions creates conduction mechanism [30]. The measure of the amount of passage of electrical current in a material is called electrical conductivity. Ac conductivity was determined by the formula:
ε′ = Cd/Aεo
σac =σ1 (T )+σ 2 (ω, T )
(6)
(9)
In Eq. (6), A is the cross-sectional area of the pellet, C is the capacitance of pellet, εo is the permittivity of free space and d is thickness of the pellet. Dielectric loss factor is given by the equation:
In Eq. (9) the first part s1 (T) is DC conductivity and the second part s2(ω,T) is frequency and temperature dependent. This part indicates the dielectric relaxation caused by bound or localized charge carriers [31]. This term can also be written as:
ϵ ′′ = ϵ′/ tan (δ )
σ 2 (ω, T ) = B (T ) ωn (T )
(7)
The dielectric loss factor (ε'') curves for all compositions of Sr2NiCoTbxFe28 xO46 nano-ferrites are shown in Fig. 7. The Fig. 7 shows that by increasing frequency the value of dielectric loss factor also found to decrease. The peaks in the Fig. 7 arises due the intrinsic electric dipole polarization and interfacial polarization [28]. Tangent loss is the ratio between loss or resistive current and charging current in the sample and is given by the equation [29]:
tan δ = ϵ″/ϵ′
(8)
The value of tangent loss is affected by several factors, such as structural homogeneity, sintering temperature and chemical composition of the materials [15]. Maxwell–Wagner theory explains that there is inverse relation between tangent loss and dielectric constant (ɛ‘) with frequency [26]. The Fig. 8 shows that
Fig. 7. Variation of dielectric loss factor with frequency of Sr2NiCoTbxFe28 xO46 X-type ferrites.
(10)
Ac conductivity of the prepared nano-ferrites could be calculated by the relation:
σac = ω ∈o ϵ″ = ω ∈o ϵ′ tan δ = 2πf ∈o ϵ′ tan δ
(11)
This equation shows that by increasing frequency the ac conductivity increases [32]. The Fig. 9 shows that ac conductivity was increased with the increased frequency. The heterogeneous model of polycrystalline structure states that polycrystalline materials are composed of conducting grains. These grains are detached by highly resistive layers (grain boundaries). At lower frequency, the resistance between the grains is large and thus ac conductivity has low value, however at higher frequency, the ac conductivity
Fig. 9. Log (ω) vs log (sac) for Sr2NiCoTbxFe28 xO46 (x¼ 0.0, 0.5, 0.10, 0.15, 0.20) X-type hexagonal ferrites.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
5
Fig. 10. Real part of electric modulus (M’) vs Frequency of Sr2NiCoTbxFe28 xO46 (x¼ 0.0, 0.5, 0.10, 0.15, 0.20) X-type hexagonal ferrites.
Fig. 12. M-H loop of Sr2NiCoTbxFe28 xO46 (x ¼ 0.00, 0.05, 0.1, 0.15, 0.2) hexagonal ferrites.
increases due to reduced resistive layers among grains. [26]. The variation of real part of electric modulus (M’) with frequency is shown in Fig. 10. At low frequency region the value of M’ is low. The value of M’ increases by increasing frequency and finally at higher frequency M’ reaches a maximum constant value for all samples [33]. The variation of imaginary part of electric modulus (M”) with frequency for all compositions of X-type hexagonal ferrites (Sr2NiCoTbxFe28 xO46) is shown in Fig. 11. The peaks in the Figure describe the conductivity relaxation. This pattern explain charge transport processes like conduction relaxation and electrical transport as a function of frequency [34]. Imaginary part of electric modulus expresses the loss of energy [35]. Cole-Cole plots are used to separate the grain and grain boundary contributions [36]. These plots unfold information about large volume of grain boundaries [37]. The density of the grain boundaries increases when Tb is added to the samples and thus the resistance of the grain boundaries also increases [38].
Table 2 Estimated saturation magnetization Ms, remanace magnetization Mr and squareness ratio of Tb doped SrNiCo-X hexagonal ferrites.
3.5. Magnetic properties Fig. 12 shows the M–H loops of Sr2NiCoTbxFe28 xO46 (x¼0.00, 0.05, 0.1, 0.15, 0.2) hexagonal nano-ferrites. The decrease in saturation magnetization (Ms) and remanance magnetization (Mr) in the range 76–54 emu/g and 27–21 emu/g respectively was found
Sub-lattice
Coordination
Block
Number of ions
Spin
6c1v 3av1 18hVI 6cvI 6cIV 3bv1
Tetrahedral Octahedral Octahedral Octahedral Tetrahedral Octahedral
S S S–T T T T
2 1 6 2 2 1
Down Up Up Down Down Up
with the increased Tb3 þ -contents. The coercivity was found to increase from 610 to 747 Oe with the increase of Tb3 þ -contents. The variations in magnetic properties may be due to the cationic distribution in different sites of S and T blocks [39]. The six different sites 6c1v, 3av1, 18hVI, 6cvI, 6cIV, 3bv1 are listed in Table 2 [2]. The variation in Ms and Mr can be explained on the basis of super exchange interaction between tetrahedral 6c1v and octahedral 3av1 sites of the S-blocks [24,40]. The replacing of iron ions with rare earth metal ions in Sr2NiCoTbxFe28 xO46 hexagonal ferrites resulted in diluting the magnetic interactions. As the iron is replaced by Tb3 þ cations, the super exchange interaction between 3av1 and 6c1v sites is reduced. This is due to the different magnetic moment of iron ions and rare earth metal (Tb3 þ ) cations (magnetic moment of iron 5μB and magnetic moment of rare earth metal 0) [40]. Therefore, the net magnetic moment of the Tbdoped SrCoNi-X type ferrites was reduced (Table 3). The coercivity (Hc) was increased with the increased Tb-contents. The values of Hc were found in the range 610–747. The enhanced coercivity is explained on the basis of c/a ratio. The c/a ratio of the prepared nano-ferrites lies in the range 15.851-15.836. This factor reduced the demagnetization factor that resulted the Table 3 Ms, Mr, Hc and squarness ratio of Sr2NiCoTbxFe28 xO46 (x ¼0.00, 0.05, 0.1, 0.15, 0.2) hexagonal ferrites.
̋
Fig. 11. Variation of imaginary part of electric modulus (M) with frequency of Sr2NiCoTbxFe28 xO46 (x¼ 0.0, 0.5, 0.10, 0.15, 0.20) X-type hexagonal ferrites.
S.no
Ms (emu/g)
Mr (emu/g)
Hc (Oe)
Squarness ratio
1 2 3 4 5
76.244 70.708 65.172 62.404 54.100
27.400 25.910 24.440 23.705 21.500
610.17 644.385 678.600 695.708 747.03
0.359 0.366 0.375 0.380 0.397
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎
6
optimization of coercivity [40,41]. The coercivity (Hc) and saturation magnetization (Ms) are related with each other by the following relation:
Hc =K1 /μo Ms
(12)
The values of coercivity Hc is greater than half of the ramanance magnetization Mr i.e (Hc 4Mr/2). The materials which have greater coercivity than half of the remanance magnetization Mr can be used for high frequency applications [40,42]. The squarness ratio was calculated from Ms and Mr values and found in the range of 0.359–0.397. All compositions exhibited the squarness values smaller than the typical value 1 for single domain isolated ferromagnetic particle [40]. The values of squarness ratio decreased with increase of doping (Tb) concentration which shows that the particles may reside as single domain. The pure SrCoNi-X ferrites have a small value of squarness ratio that shows that particles are completely randomly oriented and exist in multi domains [40].
[9]
[10]
[11]
[12]
[13]
[14]
[15]
[16]
4. Conclusions TGA curve revealed that the maximum weight loss occurred at 325 °C. The hexagonal phase was developed at 1100 °C. XRD patterns reveal that the prepared nano-ferrites have hexagonal structure. The crystalline size was increased from 22 nm to 25 nm when doping concentration of Tb was increased for x ¼0.00 to x ¼0.10 and then decreased to 15 nm as Tb-concentration was increased from x¼ 0.15 to 0.20. The FTIR spectra of nano-ferrites in the range 1362–668 cm 1 also confirmed the hexagonal phase of the prepared samples. The value of dielectric constant was 12.5 at low at frequency and abruptly decreased to 6.5 at high frequency. The incorporation of terbium lowers the saturation magnetization and remanance from 76 to 54 emu/g and 27 to 21 emu/g respectively. The coercivity was increased from 610 to 747 Oe with the increased Tb-concentration. The variations in magnetic properties may be attributed to the redistribution of cations on different sites of S and T blocks. The synthesized X-type nano-ferrites are useful in the fabrication of high frequency devices and recording media applications.
Acknowledgment One of the authors (I. Shakir) is highly thankful to the Deanship of Scientific Research, King Saud University, Riyadh for Prolific Research Group Project no. PRG-1436-25.
[17]
[18]
[19]
[20] [21]
[22]
[23]
[24]
[25] [26]
[27]
[28] [29]
[30]
References [31] [1] R.C. Pullar, Hexagonal ferrites: a review of the synthesis, properties and applications of hexaferrite ceramics, Prog. Mater. Sci. 57 (2012) 1191–1334. [2] G. Albanese, Recent advances in hexagonal ferrites by the use of nuclear spectroscopic methods, Le Journal De Physique Colloques 38 (1977), C1-85C81-C94. [3] F. Aen, S.B. Niazi, M. Islam, M. Ahmad, M. Rana, Effect of holmium on the magnetic and electrical properties of barium based W-type hexagonal ferrites, Ceram. Int. 37 (2011) 1725–1729. [4] G.M. Rai, M. Rana, Dielectric and magnetic behavior of BaCd2 xSrxFe16O27 w-type hexagonal ferrites, J. Alloy. Compd. 509 (2011) 4793–4796. [5] G. Ben-Xi, L. Huai-Xian, D. You-Wei, Magnetic properties and Mössbauer spectra of X type hexagonal ferrites, J. Magn. Magn. Mater. 31 (1983) 803–804. [6] I. Sadiq, I. Khan, E.V. Rebrov, M.N. Ashiq, S. Naseem, M. Rana, Structural, infrared, magnetic and microwave absorption properties of rare earth doped X-type hexagonal nanoferrites, J. Alloy. Compd. 570 (2013) 7–13. [7] B. Gu, Magnetic properties of X‐type Ba2Me2Fe28O46 (Me¼ Fe, Co, and Mn) hexagonal ferrites, J. Appl. Phys. 71 (1992) 5103–5106. [8] Z. Haijun, L. Zhichao, Y. Xi, Z. Liangying, W. Mingzhong, Dielectric and
[32] [33]
[34]
[35] [36]
[37]
magnetic properties of ZnCo-substituted X hexaferrites prepared by citrate sol–gel process, Mater. Res. Bull. 38 (2003) 363–372. F. Leccabue, R. Panizzieri, S. Garcia, N. Suarez, J. Sanchez, O. Ares, X.R. Hua, Magnetic and mössbauer study of rare-earth-substituted M-, W-and X-type hexagonal ferrites, J. Mater. Sci. 25 (1990) 2765–2770. I. Sadiq, I. Khan, E.V. Rebrov, M. Naeem Ashiq, S. Naseem, I. Shakir, M.U. Rana, Influence of Sm–Mn substitution on structural, dielectric and electrical properties of X-type hexagonal nanoferrites, J. Chem. Soc. Pak. 37 (2015) 33–38. I. Sadiq, S. Naseem, M. Rana, M.N. Ashiq, I. Ali, Temperature dependent magnetic and microwave absorption properties of doubly substituted nanosized material, J. Magn. Magn. Mater. 385 (2015) 236–242. I. Sadiq, I. Ali, E. Rebrov, S. Naseem, M.N. Ashiq, M. Rana, Nanosized Ce–Zn substituted microwave absorber material for X-band applications, J. Magn. Magn. Mater. 370 (2014) 25–31. S.Y. An, I.-B. Shim, C.S. Kim, Mössbauer and magnetic properties of Co–Ti substituted barium hexaferrite nanoparticles, J. Appl. Phys. 91 (2002) 8465–8467. K.K. Mallick, P. Shepherd, R.J. Green, Dielectric properties of M-type barium hexaferrite prepared by co-precipitation, J. Eur. Ceram. Soc. 27 (2007) 2045–2052. I. Sadiq, I. Ali, E.V. Rebrov, S. Naseem, M.N. Ashiq, M. Rana, Influence of Nd–Co substitution on structural, electrical, and dielectric properties of X-type hexagonal nanoferrites, J. Mater. Eng. Perform. 23 (2014) 622–627. H.-I. Hsiang, R.-Q. Yao, Hexagonal ferrite powder synthesis using chemical coprecipitation, Mater. Chem. Phys. 104 (2007) 1–4. T. Strukturne, N.I.M.L. Prahov, Structural, thermal and magnetic properties of barium-ferrite powders substituted with Mn, Cu or Co and X (X ¼ Sr and Ni) prepared by the sol–gel method, Mater. Technol. 46 (2012) 305–310. Z. Haijun, L. Zhichao, M. Chenliang, Y. Xi, Z. Liangying, W. Mingzhong, Preparation and microwave properties of Co-and Ti-doped barium ferrite by citrate sol–gel process, Mater. Chem. Phys. 80 (2003) 129–134. S. Kulkarni, J. Shrotri, C. Deshpande, S. Date, Synthesis of chemically coprecipitated hexagonal strontium-ferrite and its characterization, J. Mater. Sci. 24 (1989) 3739–3744. M. Azim, S. Atiq, S. Naseem, Structural and electrical characterization of lanthanum doped strontium hexaferrites, Sci. Int. 24 (2012) 341. M. Ahmed, N. Okasha, R. Kershi, Dramatic effect of rare earth ion on the electrical and magnetic properties of W-type barium hexaferrites, Phys. B: Condens. Matter 405 (2010) 3223–3233. P.A. Kumar, J. Shrotri, S. Kulkarni, C. Deshpande, S. Date, Low temperature synthesis of Ni0.8Zn0.2Fe2O4 powder and its characterization, Mater. Lett. 27 (1996) 293–296. R. Jotania, R. Khomane, C. Chauhan, S. Menon, B. Kulkarni, Synthesis and magnetic properties of barium–calcium hexaferrite particles prepared by sol– gel and microemulsion techniques, J. Magn. Magn. Mater. 320 (2008) 1095–1101. A. Elahi, M. Ahmad, I. Ali, M. Rana, Preparation and properties of sol–gel synthesized Mg-substituted Ni2Y hexagonal ferrites, Ceram. Int. 39 (2013) 983–990. C. Chen, J. Cheng, S. Yu, L. Che, Z. Meng, Hydrothermal synthesis of perovskite bismuth ferrite crystallites, J. Cryst. Growth 291 (2006) 135–139. Z. Anwar, M.A. Khan, I. Ali, M. Asghar, M. Sher, I. Shakir, M. Sarfraz, M.F. Warsi, Investigation of dielectric behavior of new Tb3 þ doped BiFeO3 nanocrystals synthesized via micro-emuslion route, J. Ovonic Res. 10 (2014) 265–273. R. Kambale, P. Shaikh, C. Bhosale, K. Rajpure, Y. Kolekar, Dielectric properties and complex impedance spectroscopy studies of mixed Ni–Co ferrites, Smart Mater. Struct. 18 (2009) 085014. Z. Haijun, Y. Xi, Z. Liangying, The preparation and microwave properties of Ba2ZnxCo2 xFe28O46 hexaferrites, J. Magn. Magn. Mater. 241 (2002) 441–446. Iqbal Muhammad Jave d, Ashiq Muhammad Naeem, Gomez Pablo Hernandez, Effect of doping of Zr–Zn binary mixtures on structural, electrical and magnetic properties of Sr-hexa ferrite nanoparticles, J. Alloy. Compd. 478 (2009) 736–740. A.A. El Ata, M. El Nimr, D. El Kony, A. Al-Hammadi, Dielectric and magnetic permeability behavior of BaCo2 x NixFe16O27 w-type hexaferrites, J. Magn. Magn. Mater. 204 (1999) 36–44. M. El Hiti, Dielectric behavior and ac electrical conductivity of Zn-substituted Ni Mg ferrites, J. Magn. Magn. Mater. 164 (1996) 187–196. A.A. El Ata, M. Ahmed, Dielectric and AC conductivity for BaCo2 xCuxFe16O27 ferrites, J. Magn. Magn. Mater. 208 (2000) 27–36. M.A. Iqbal, I. Ali, H.M. Khan, G. Mustafa, I. Ali, Study of electrical transport properties of Eu þ 3 substituted MnZn-ferrites synthesized by co-precipitation technique, Ceram. Int. 39 (2013) 1539–1545. M.N. Ashiq, M.J. Iqbal, I.H. Gul, Structural, magnetic and dielectric properties of Zr–Cd substituted strontium hexaferrite (SrFe12O19) nanoparticles, J. Alloy. Compd. 487 (2009) 341–345. I. Gul, A. Maqsood, Structural, magnetic and electrical properties of cobalt ferrites prepared by the sol–gel route, J. Alloy. Compd. 465 (2008) 227–231. M. Chourashiya, J. Patil, S. Pawar, L. Jadhav, Studies on structural, morphological and electrical properties of Ce1 xGdxO2 (x/2), Mater. Chem. Phys. 109 (2008) 39–44. H. Rodrigues, G.P. Junior, A. Sales, P. Silva, B. Costa, P. Alcantara, S. Moreira, A. Sombra, BiFeO3 ceramic matrix with Bi2O3 or PbO added: Mössbauer, Raman and dielectric spectroscopy studies, Phys. B: Condens. Matter 406 (2011) 2532–2539.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i
J. Rehman et al. / Ceramics International ∎ (∎∎∎∎) ∎∎∎–∎∎∎ [38] R. Choudhary, D.K. Pradhan, C. Tirado, G. Bonilla, R. Katiyar, Impedance characteristics of Pb (Fe2/3W1/3) O3–BiFeO3 composites, Phys. Status Solidi (b) 244 (2007) 2254–2266. [39] M.A. Gabal, W. Bayoumy, Effect of composition on structural and magnetic properties of nanocrystalline Ni0.8 xZn0.2MgxFe2O4 ferrite, Polyhedron 29 (2010) 2569–2573. [40] I. Ali, M. Islam, M.N. Ashiq, M.A. Iqbal, M. Awan, S. Naseem, Role of Tb–Mn substitution on the magnetic properties of Y-type hexaferrites, J. Alloy. Compd.
7
599 (2014) 131–138. [41] X. Liu, W. Zhong, S. Yang, Z. Yu, B. Gu, Y. Du, Influences of La3 þ substitution on the structure and magnetic properties of M-type strontium ferrites, J. Magn. Magn. Mater. 238 (2002) 207–214. [42] Y. Li, R. Liu, Z. Zhang, C. Xiong, Synthesis and characterization of nanocrystalline BaFe9.6Co0.8Ti0.8M0.8O19 particles, Mater. Chem. Phys. 64 (2000) 256–259.
Please cite this article as: J. Rehman, et al., Structural, magnetic and dielectric properties of terbium doped NiCoX strontium hexagonal nano-ferrites synthesized via micro-emulsion route, Ceramics International (2016), http://dx.doi.org/10.1016/j.ceramint.2016.02.171i