Doping effect of Sm3+ on magnetic and dielectric properties of Ni-Zn ferrites

Author’s Accepted Manuscript Doping effect of Sm3+ on magnetic and dielectric properties of Ni-Zn ferrites Zhiqing Liu, Zhijian Peng, Changchun Lv, Xiuli Fu

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To appear in: Ceramics International Received date: 20 August 2016 Revised date: 19 September 2016 Accepted date: 17 October 2016 Cite this article as: Zhiqing Liu, Zhijian Peng, Changchun Lv and Xiuli Fu, Doping effect of Sm3+ on magnetic and dielectric properties of Ni-Zn ferrites, Ceramics International, http://dx.doi.org/10.1016/j.ceramint.2016.10.112 This is a PDF file of an unedited manuscript that has been accepted for publication. As a service to our customers we are providing this early version of the manuscript. The manuscript will undergo copyediting, typesetting, and review of the resulting galley proof before it is published in its final citable form. Please note that during the production process errors may be discovered which could affect the content, and all legal disclaimers that apply to the journal pertain.

Doping effect of Sm3+ on magnetic and dielectric properties of Ni-Zn ferrites Zhiqing Liu1,2, Zhijian Peng1,a, Changchun Lv1, Xiuli Fu2,b 1

School of Engineering and Technology, China University of Geosciences, Beijing 100083, P. R. China

2

School of Science, Beijing University of Posts and Telecommunications, Beijing 100876, P. R. China

[email protected] [email protected] *Correspondence

concerning this paper directly to: Prof. Dr. Zhijian Peng, School of Engineering and

Technology, China University of Geosciences at Beijing, Beijing 100083, P. R. China. Tel: 86-10-82320255; Fax: 86-10-82322624 *Correspondence

to:Prof. Dr. Xiuli Fu, School of Science, Beijing University of Posts and

Telecommunications, Beijing 100876, P. R. China. Tel: 86-10-62282452; Fax: 86-10-62282054

Abstract

Ni-Zn ferrites of nominal composition Ni0.5Zn0.5SmxFe2-xO4 (x=0-0.1) were prepared by a conventional two-steps solid sintering method. The effect of Sm3+ doping on the microstructural, magnetic and dielectric properties of the as-prepared Ni-Zn ferrites were investigated. The main phase of all the samples was ferrite spinel, and the samples doped with Sm3+ ions contained a small amount of a foreign SmFeO3 phase as well. And the doping of Sm3+ resulted in the increase of lattice constant. The grain size, density and densification of the ferrites initially decreased after Sm3+ doping, but then increased with more Sm3+ doped. With increasing substitution level, x, the saturation magnetization of the as-prepared ferrites decreased, while the coercivity increased. The Curie temperature raised initially and decreased later with increasing content of Sm3+ in the samples, reaching a maximum of 274 ºC when x=0.025. The initial permeability of the ferrites first decreased and then increased with 0

increasing doping amount of Sm3+ ions. The introduction of Sm3+ ions into Ni-Zn ferrite would lead to the reduced dielectric loss in the frequency range of 1-100 MHz, but the dielectric loss raised when more Sm3+ was added in the frequency range of 100-1000 MHz. When x=0.05, the dielectric loss reached the lowest value.

Keywords: Ni-Zn ferrite; Doping; Sm; Electromagnetic properties

1. Introduction Soft magnetic ferrites are one of the most used nonmetallic magnetic materials, because of their high resistivity and low power loss. They include Mn-Zn, Ni-Zn and Mg-Zn ferrites, in which the Ni-Zn ferrites have much higher operating frequency, Cure temperature and resistivity compared with the other two series of ferrites. And public attention has been aroused to the importance of Ni-Zn ferrites because their new applications, such as modern communication, internet, electrical appliance, computer circuitry and anti-electromagnetic disturbing technology, are rapidly expanding [1-3]. The excellent magnetic properties of Ni-Zn ferrite were first reported by Snoek in 1947 [2]. Ni-Zn ferrite polycrystalline materials are of an inverse spinel structure and belong to the Fd3m space group. The chemical formula of Ni-Zn ferrites can be presented as (ZnxFe1-x)[Ni1-xFe1+x]O4. And their crystal structure consists of two crystallographically distinct locations named as tetrahedral A and octahedral B sites, where the parentheses and square brackets denote the tetrahedral A and octahedral B sites, respectively. And the metal cations located in tetrahedral A and octahedral B sites have either four- or six-fold coordination in the spinel structure [4]. Such structure endows them with unique electromagnetic properties. However, up to now many issues have remained to be addressed to meet the demands for miniaturization, broader relative band width, higher operating frequencies, and reduced costs [2]. Moreover, Ni-Zn ferrites are not only a magnetic medium, but also a dielectric medium. The dielectric 1

property of a Ni-Zn ferrite is also very important, which is a measure of the ability to store the charge of the ferrite. In particular, the frequency stability of Ni-Zn ferrites has become a necessary technical parameter because of their applications in high density magnetic storage, electronic and microwave devices, sensors, and magnetically guided drug delivery [5]. In recent years, scientists worldwide have paid great attention in the high-frequency applications of low-cost soft magnetic Ni-Zn ferrites [1-3]. Therefore, different aspects of materials processing and effect of additives on their properties and applications have been investigated by many literatures [6-9]. With regard to the additives, many magnetic and non-magnetic ions were chosen as the dopants for Ni-Zn ferrites, in which many metal cations can impose an influence on their magnetic and dielectric properties [8-14]. For example, the increase in saturation magnetization was reported in Ni-Zn ferrite by the doping of Co2+ [8]. The improvement of permeability of Ni-Zn ferrite could be realized by the incorporation of a small amount of V2O5 [9]. And the study of rare earth doped ferrites was first reported by Rezlescu et al., which indicated that an important modification on the electromagnetic properties could be obtained by introducing a relatively small amount of rare-earth ions replacing Fe3+ [10]. Since then, many investigations have been carried out to make further improvements on the magnetic and dielectric properties of rare-earth substituted ferrites [11-14]. The results have shown that, certain amount of rare-earth ions could enter into the octahedral B sites of Ni-Zn ferrites, replacing the Fe3+ ions in the lattice. Thus, a small amount of Fe ions substituted by rare-earth ions could drastically affect the physical properties of the ferrites due to the larger ionic radius, and special electrical and magnetic properties of rare-earth ions. Among the rare-earth additives reported in literature, Sm3+ ions, specifically, could result in quite significant effects on the magnetic and electric properties of the Ni-Zn ferrites [15,16]. Rezlescu et al. [17] pointed out that Sm3+ ions, after doping into Ni-Zn ferrites, could form insulating intergranular layers at the grain boundaries, impeding the oxidation of Fe2+ ions inside the grains during slow cooling of the samples, and increasing the 2

resistivity of the materials. However, the dielectric properties of Ni-Zn ferrites doped with Sm3+ ions at high frequencies have not been clear yet. In the present work, Sm-substituted Ni-Zn ferrites with a nominal composition of Ni0.5Zn0.5SmxFe2-xO4 (where x=0-0.1 with a step of 0.025) were prepared by a conventional two-steps solid sintering method. The doping effect of Sm3+ on the magnetic and dielectric popreties of Ni-Zn ferrites at high frequency (in the range of 1-1000 MHz) were systematically investigated. One of the aims of this work is to establish the relationship between the content of Sm3+ ions and their electromagnetic poperties. The results indicated that an appropriate amount of Sm3+ doping into Ni-Zn ferrites could improve their temperature stability and the proposed materials might be promising in high-frequency applications.

2. Experimental procedures 2.1 Samples preparation The Sm3+ doped Ni-Zn ferrites with a nominal composition of Ni0.5Zn0.5SmxFe2-xO4 (where x=0, 0.025, 0.05, 0.075, 0.1) were prepared by a conventional two-steps solid sintering method. The raw materials were analytical grade NiO, ZnO, Fe2O3 and Sm2O3 powders. The weight of the grinding media (TZP ZrO2 balls) to the raw materials was 3:1. During the processing, all the raw powders and the dispersant (0.5 wt.% Davon C) were first mixed in a ball mill, and then milled with 50 ml distilled water for 36 h. The milled slurries were dried in an oven at 120 ºC, and then the dried powder mixtures were pre-sintered in a muffle furnace at 800 ºC for 3 h. After that, the pre-sintered powder chunks were ground into powders again, and the binder (0.5 wt.% PVA) was added into the powders for ganulation. After ganulation, the obtained powders were pressed into pellets (6 mm in diameter and 1 mm in thickness, or 12 mm in diameter and 1 mm in thickness) and toroidal rings (20 mm in outer diameter, 10 mm in inner diameter and 3 mm in thickness) by a hydraulic press. Finally, All the samples were sintered for 4 h in a muffle furance at 1250 ºC, and then the samples were cooled down in the furnace to room temperature. 3

2.2 Materials characterization The crystallographic analysis of the samples was performed with the pellets of 6 mm diameter and 1 mm thickness by X-ray diffraction (XRD, D/max-RB, Cu Kα, λ=1.5418 Å). The scanning 2θ angle was in the range of 20 to 80º, and the scanning rate was 8 º/min. The apparent density of the samples was measured by Archimedean principle according to the international standard ISO18754. The density of the unit cell was used as the theoretical density of the ferrites. And the relative density of the samples was defined as the percentage of the apparent density to their corresponding theoretical density. The diameter shrinkage was the linear shrinkage in sample diameter, which was calculated as the percentage of the diameter difference between the green and sintered ones on the basis of geometric dimension measurement. The microstructure of samples was examined on their surfaces by using scanning electron microscope (SEM, SU8020). A vibrating sample magnetometer (VSM, LakeShore 7307) with a maximum magnetic field of 10 KOe was used to measure the saturation magnetization (Ms), coercivity (Hc) and Curie temperature (Tc) of the samples with the pellets of 6 mm diameter and 1 mm thickness. The toroidal rings (20 mm in outer diameter, 10 mm in inner diameter and 3 mm in thickness) and pellets (12 mm in diameter and 1 mm in thickness) were used to measure the initial permeability (μi) and complex permittivity (ε=ε´+ε´´), respectively, by an impedance analyzer (Agilent E4991A) within the frequency from 1 MHz to 1 GHz. All these electromagnetic measurements were carried out at room temperature except Tc.

3. Results and Discussion 3.1 Compositional and structural properties The phase and crystalline structure of the as-prepared samples were analyzed by XRD, and typcial XRD patterns of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0-0.1) are shown in Fig. 1. As seen from this figure, the main phase of all the samples was ferrite spinel, and the Ni-Zn ferrites doped with Sm3+ ions contained a small amount of a foreign phase, which was identified as SmFeO3 (JCPDS No. 39-1490). And the content of SmFeO3 increased 4

with increasing doping amount of Sm3+. The lattice parameter of the as-prepared samples was calculated from the XRD data, and the results are listed in Table 1. From this table, it is seen that the lattice constant increased after the doping of Sm3+, which is similar with the results reported by other researchers [10]. The reason of the variation of lattice constant is that, the doped samarium ions could enter into the crystal lattice of the spinel, locating at the octahedral B sites with adequate space, substituting for the Fe3+ ions. And because the radius of Sm3+ ion is larger (0.96 Å) than that of Fe3+ one (0.67 Å), so the replacement of Fe3+ ions in the octahedral B sites by Sm3+ ions would cause the expansion of the unit cell, finally resulting in the increase in lattice constant. The microstructures of the prepared samples doped with different amounts of Sm3+ ions were examined on the polished surfaces by SEM microscopy, and typical SEM micrographs are displayed in Fig. 2. From the obtained SEM micrographs, the grain sizes of the corresponding samples were evaluated by software Lince PC, and the results are also listed in Table 1. It is seen that the grain size of the ferrites in the prepared samples initially decreased after the doping of Sm3+ ions, but increased when the doping amount of Sm3+ ions increased further, in which the Sm-substituted Ni-Zn ferrite samples with doping level x=0.05 presented the smallest grain size. The variation of grain size can be explained as follows. After the addition of Sm3+ ions, the formed SmFeO3 phase, as mentioned in the XRD results, would pin at the grain boundaries, impeding the growth of ferrite grains, resulting in smaller gain size. Moreover, the bonding energy of Sm3+-O2- is larger than that of Fe3+-O2-, and the formation of Sm3+-O2- needs more energy. Therefore, when Sm3+ ions were doped into the Ni-Zn ferrites, more energy was needed in the mass transfer process, which also impeded the growth of ferrite grains [12]. However, when the doping amount of Sm3+ ions increased, some divalent Fe2+ ions were replaced by Sm3+ ions in the grain boundary region, so the amount of metallic ion vacancies in vicinity increased in order to keep the balance of electric charges, which would result in the increase of the grain boundary movement speed. Thereby, the size of the ferrite 5

grains increased with further addition of Sm3+ ions [18]. The apparent densities and relative densities as well as diameter shrinkage of the as-prepared samples are also listed in Table 1. It can be seen that, the density, relative density and shrinkage of the samples decreased first after the addition of Sm3+ ions, but then increased slightly with the further addition of Sm3+ ions, indicating that the doping of Sm3+ ions into Ni-Zn ferrites would reduce the densification of the samples, which is similar with the result reported in Ref. [15]. In the present work, the lowest relative density (91.34%) and shrinkage (15.69%) were reached for the samples of Ni0.5Zn0.5SmxFe2-xO4 with x=0.05. The reason for the variations of relative densities and diameter shrinkage can be explained as follows. The formation of SmO2 during the sintering process would promote the growth of grains with inner pores [15]; so, the relative densities and diameter shrinkage decreased with the addition of Sm3+ at first. However, the amount of metallic ion vacancies in vicinity increased with the additional Sm3+ doping as stated in the last paragraph, which would result in the increase of relative densities and diameter shrinkage. The variation of densities is not only correlated to the densification, but also effected by the formation of foreign phase SmFeO3. Because the densification decreased first and increased later, in combination with the increasing amount of the formed SmFeO3 with much higher density than pure Ni-Zn ferrites, the density of the samples initially decreased and then increased with increasing doping level of Sm3+ ions. 3.2 Magnetic performance The hysteresis loops and temperature dependence of magnetization for the prepared Ni0.5Zn0.5SmxFe2-xO4 are shown in Figs. 3 and 4. From these figures, their basic magnetic parameters were calculated (see Table 2). It can be seen that, as the content of Sm, x, increased from 0 to 0.1, the value of the Ms gradually decreased. It is known that the Ms of the ferrites can be estimated by the following equation, Ms=|MB-MA|,

(1) 6

where MB is the magnetic moment in B sites (the total magnetic moment of Ni2+, Fe3+ and Sm3+) and MA is the magnetic moment in A sites (the total magnetic moment of Zn2+ and Fe3+) [19]. After the substitution of Fe3+ ions by Sm3+ ions, because the magnetic moment of substituting Sm3+ ions (3 μB) is samller than that of original Fe3+ ions (5 μB), the magnetization of B-sublattice decreases, so the observed decrease in Ms with the increase in the doping amount of Sm3+ ions could be expected. In addition, the Ms depends on the movement of domain wall [12]. Because of the movement of domain wall was hindered by the foreign phase SmFeO3 in the present Ni-Zn ferrites, the effect of the foreign phase should be larger than that of the applied magnetic field during the process of domain wall movement. Thus, the Ms decreased because the movement became harder. The Hc of the prepared samples increased with increasing substitution level of Sm3+ ions, x. The Hc of soft ferrites is caused by the resistance of domain wall displacement. Because domain wall movement requires less energy than that required by domain rotation in the magnetization or demagnetization process, so the larger the grains, the easier the domain walls displacement [20]. However, because the grain size in the present ferrite samples did not change significantly, which fluctuated between 2.42 and 3.11 µm, therefore the main cause accounting for the increase of Hc was not the grain size. It can be explained as follows. Because the foreign phase SmFeO3 pinning at the grain boundaries would break and prevent the displacement of domain walls [12], the formation of foreign phase SmFeO3 in the present Ni-Zn ferrites was much more effective to increase their Hc. The Tc of the present Ni-Zn ferrites increased first after the doping of Sm3+ ions, and then dropped down with further increased x. The Tc of ferrites depends on three kinds of exchange effect, A-A, B-B, and A-B, in which the A-B exchange effect is the strongest one. In Ni–Zn ferrites, the tetrahedral A sites are occupied actually by Zn2+, Fe2+ and Fe3+ ions, and the octahedral B sites are done by Ni2+, Fe2+ and Fe3+ ions. So, the interaction between Fe3+ ions occupying the A and B sites plays a leading role in Tc [21]. Generally, the partial reduction of Fe3+ to Fe2+ would take place in the sintering atmosphere, and the A-B exchange effect between Fe3+ and Fe2+ was weaker 7

than that between Fe3+ and Fe3+ ions. However, the doping of small amount Sm3+ ions could enter into the octahedral B sites and limit the reduction reaction of Fe3+ to Fe2+ in the B sites. So, it would increase the concentration of Fe3+ and enhance the A-B exchange effect. Finally, the Tc increased with the addition of Sm3+. On the other hand, with increasing doping amount of Sm3+ ions, the Sm3+ ions would substitute the Fe3+ ions, and the A-B exchange effect between Fe3+ (A sites) and Sm3+ (B sites) was much weaker than that of Fe3+ ions; so, the A-B exchange effect in the obtained ferrites was reduced. As a result, the total exchange in the ferrites was weakened, finally resulting in decreased Tc. The frequency dependence of the initial permeability of the prepared Ni-Zn ferrites is plotted in Fig. 5. The variation presents the same trendency as that of grain size with the doping level of Sm. The initial permeability of the present ferrites initially decreased but then increased with increasing doping amount of Sm3+ ions, in which the samples with a doping level x=0.05 possessed the smallest initial permeability. The initial permeability of Ni-Zn ferrites is related to the microstructure of samples because of the two different magnetizing mechanisms: the domain rotation and domain wall displacement [22]. And the domain rotation needs much more energy than that of domain wall displacement [23]. Thus, the smaller the grain size, the harder the movement of domain wall displacement. Moreover, the foreign phase SmFeO3 pinning at the grain boundaries would break and prevent the displacement of domain walls. Thereby, the decrease of initial permeability is expected. However, with further addition of Sm3+ ions, the size of the ferrite grains increased as listed in Table 1, which would cause the domain wall movement become much easier. As a result, the initial permeability increased with further additional Sm3+ doping. Therefore, the variation presents a similar trendency with that of grain size as the content of Sm in the samples varies. 3.3 Dielectric performance The dielectric loss tangent (tanδ), defined as ε´´/ε´, is one of the most important properties of ferrites, which 8

estimates the eddy-current loss of ferrites in the alternating electric field. It depends on the processing and sintering conditions, chemical composition, and type of the additives. The frequency dependence of the dielectric loss tangent of the present Ni-Zn ferrite samples is shown in Fig. 6. It can be seen that the introduction of Sm3+ ions into the Ni-Zn ferrites would reduce the value of the tanδ of the samples in comparation with that of the pure Ni-Zn ferrite in the frequency range of 1-100 MHz, especially for the samples with the doping level x=0.025 and 0.05. And it would increase sharply in the high-frequency region (100-1000 MHz) with the further addition of Sm3+ ions. The increase in conductivity indicates not only an increased number of charge carriers, but also an enhanced hopping rate of charge between the charge carriers Fe2+ and Fe3+. The hopping rate of charge is enhanced when the frequency of an applied field increases, thus resulting in increased conductivity, which is the most significant contribution to the dielectric loss tangent (tanδ) of the present samples. Such phenomenon can be explained on the basis of Koop’s two layers model [24], which supposes that the substituted Ni-Zn ferrites consist of conducting grains separated by thin layers (grain boundaries) of highly resistivity. According to this model, the dielectric behavior of the present Ni-Zn ferrites at low frequency can be described as a grain boundary behavior, whereas the dispersion at high frequency might be attributed to the conductivity of the grains [25]. Because Sm3+ ions, after doped into Ni-Zn ferrites, could form insulating intergranular layers on the grain boundaries, so the dielectric loss tangent (tanδ) of the present Ni-Zn ferrite samples doped with of Sm3+ ions is lower than that of pure Ni-Zn ferrites in the low-frequency region (1-100 MHz), which is determined by the conductivity of the thin intergranular layers. Furthermore, the electron exchange is correlated to the porosity, and the porosity of the present ferrites increased with increasing doping level of Sm3+ ions, which would limit the transmission of charge carriers. Therefore, an initial decrease in electron exchange between Fe2+ and Fe3+ is expected, which is accompanied always by lower dielectric loss tangent. That is, the decreased porosity resulted in the higher dielectric loss tangent. 9

However, the dielectric loss tangent (tanδ) of the samples increased sharply in the high-frequency region (100-1000 MHz), which depended on the conductivity of the grains. It is well known that the dielectric behavior of ferrite grains strongly depends on the electron exchange interaction between Fe2+ Fe3+ [26]. The conductivity of ferrite grains depends on the number of available Fe2+ ions in the octahedral sites. The electronic exchange Fe2+Fe3+ results in a local displacement of electrons, which determines the polarization and thus the dielectric constant of the ferrites. For the present Ni-Zn ferrites doped with Sm3+ ions, where some Sm3+ ions entered into the octahedral B sites, and the electrical conduction took place through the electron exchange interaction Fe2+Fe3+ in the octahedral B sites. Furthermore, the doping of a small amount of Sm3+ ions would limit the reduction reaction of Fe3+ to Fe2+ in sintering atmosphere, and the concentration of Fe2+ is proportional to the total concentration of Fe element [12]. Based on the statement above, Fe2+ concentration in octahedral B sites for the sample with x=0 is higher than that of the samples with x=0.025 and 0.05. So the value of dielectric loss tangent of the samples with x=0.025 and 0.05 would be lower when compared that of pure Ni-Zn ferrite. However, because the thin layer of SmFeO3 would be formed with additional Sm3+ doped, which would impede the oxidation of Fe2+ ions inside the grains during slow cooling of the samples [11], therefore, the concentration of Fe2+ became much higher when more Sm3+ was added. As a result, a comparatively higher value of dielectric loss is expected for the Ni-Zn ferrites with x=0.075 and 0.1.

4. Conclusions Ni-Zn ferrites with different doping levels of Sm3+ ions (Ni0.5Zn0.5SmxFe2-xO4) were prepared by conventional two-steps solid sintering method. The conclusions of this study can be summarized as follows: (1) The main phase of all the samples was ferrite spinel, and the samples doped with Sm3+ ions contained a small amount of a foreign SmFeO3 phase. The lattice constants of the Sm-doped samples increased compared with the pure Ni-Zn ferrites. The grain size and relative density initially reduced with Sm3+ doping, and then raised 10

with additional Sm3+ doping. (2) The saturation magnetization of the ferrite decreased with increasing substitution level of Sm3+ ions, but the coercivity presented an opposite trend to Ms. And their Cure temperature initially raised with Sm3+ doping, and then dropped down with additional Sm3+ doping, reaching the highest value when x=0.025. The initial permeability reduced first with Sm3+ doping, and then increased when more Sm3+ was added. (3) The doping of Sm3+ ions into Ni–Zn ferrites could decrease the dielectric loss in the frequency range of 1-100 MHz, but the dielectric loss raised when more Sm3+ was added in the frequency range of 100-1000 MHz. When x=0.05, the dielectric loss reached the lowest value.

Acknowledgements This work was supported by the National Natural Science Foundation of China (grant nos. 11674035, 11274052 and 61274015), and Excellent Youth Teachers Foundation in China University of Geosciences from the Fundamental Research Funds for the Central Universities.

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Fig. 1 XRD patterns of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1). Fig. 2 SEM micrographs on the surfaces of the prepared Ni0.5Zn0.5SmxFe2-xO4: (a) x=0, (b) x=0.025, (c) x=0.05, (d) x=0.075, and (e) x=0.1. Fig. 3 Hysteresis loops of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1). Fig. 4 Temperature dependence of magnetization for the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1). Fig. 5 Frequency dependence of the initial permeability of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1). Fig. 6 Frequency dependence of the dielectric loss tangent (tanδ) of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1).

Table 1 Basic structural parameters of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1) Diameter shrinkage (%)

Apparent density (g/cm3)

Relative density (%)

Lattice constant (Å)

Grain size (μm)

Ni0.5Zn0.5Fe2O4 Ni0.5Zn0.5Sm0.025Fe1.975O4

18.32 16.02

5.10 5.13

92.64 92.53

8.381 8.402

3.07 2.59

Ni0.5Zn0.5Sm0.05Fe1.95O4

15.69

5.09

91.34

8.390

2.42

Ni0.5Zn0.5Sm0.075Fe1.925O4

15.94

5.17

92.11

8.401

2.70

Ni0.5Zn0.5Sm0.01Fe1.9O4

15.94

5.28

93.41

8.411

3.11

Nominal composition

14

Table 2 Basic magnetic parameters of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1) Nominal composition

Ms (emu/g)

Hc (Oe)

TC (ºC)

72.07 62.59 61.50 58.49 55.51

1.85 3.10 3.12 3.28 3.72

256 274 261 250 239

Ni0.5Zn0.5Fe2O4 Ni0.5Zn0.5Sm0.025Fe1.975O4 Ni0.5Zn0.5Sm0.05Fe1.95O4 Ni0.5Zn0.5Sm0.075Fe1.925O4 Ni0.5Zn0.5Sm0.01Fe1.9O4

Zhiqing Liu, et al., Ceramics International, Figure 1.

Fig. 1 XRD patterns of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1).

15

Zhiqing Liu, et al., Ceramics International, Figure 2.

16

Fig. 2 SEM micrographs on the surfaces of the prepared Ni0.5Zn0.5SmxFe2-xO4: (a) x=0, (b) x=0.025, (c) x=0.05, (d) x=0.075, and (e) x=0.1.

Zhiqing Liu, et al., Ceramics International, Figure 3.

Fig. 3 Hysteresis loops of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1).

Zhiqing Liu, et al., Ceramics International, Figure 4.

17

Fig. 4 Temperature dependence of magnetization for the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1).

Zhiqing Liu, et al., Ceramics International, Figure 5.

Fig. 5 Frequency dependence of the initial permeability of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1).

Zhiqing Liu, et al., Ceramics International, Figure 6. 18

Fig. 6 Frequency dependence of the dielectric loss tangent (tanδ) of the prepared Ni0.5Zn0.5SmxFe2-xO4 (x=0, 0.025, 0.05, 0.075, 0.1).

19