Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3

Accepted Manuscript Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3 Dengwei Hu, Fan Zhao, Lei Miao, Zhen Zhang, Yan Wang, Hualei Cheng, Yinfeng Han, Meijuan Tian, Hongxi Gu, Rong Ma PII:

S0272-8842(19)30348-7

DOI:

https://doi.org/10.1016/j.ceramint.2019.02.047

Reference:

CERI 20770

To appear in:

Ceramics International

Received Date: 2 December 2018 Revised Date:

18 January 2019

Accepted Date: 9 February 2019

Please cite this article as: D. Hu, F. Zhao, L. Miao, Z. Zhang, Y. Wang, H. Cheng, Y. Han, M. Tian, H. Gu, R. Ma, Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3, Ceramics International (2019), doi: https://doi.org/10.1016/j.ceramint.2019.02.047. 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 proof before it is published in its final 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.

ACCEPTED MANUSCRIPT 1

Magnetic properties and microstructures of a Ni-Zn ferrite ceramics co-doped with V2O5 and MnCO3

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Dengwei Hu∗, Fan Zhao∗, Lei Miao, Zhen Zhang, Yan Wang, Hualei Cheng, Yinfeng Han, Meijuan

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Tian, Hongxi Gu and Rong Ma,

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Faculty of Chemistry and Chemical Engineering, Engineering Research Center of Advanced

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Ferroelectric Functional Materials, Key Laboratory of Phytochemistry of Shaanxi Province, Baoji

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University of Arts and Sciences, 1 Hi-Tech Avenue, Baoji, Shaanxi, 721013 P. R. China

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The present work investigated the effect of the addition of V2O5 and MnCO3 on

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the microstructure and magnetic properties of Ni-Zn ferrite ceramic samples prepared

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by a conventional ceramic sintering method at different temperatures. With this aim, a

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series of samples were prepared by varying the loadings of V2O5-MnCO3 (un-doped,

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0.4–0.1 wt%, 0.1–0.4 wt%, 0.2–0.3 wt%, 0.3–0.2 wt%, and 0.5–0.1 wt%, denoted as

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sample 1, sample 2, sample 3, sample 4, sample 5, and sample 6, respectively). The

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initial permeability and power loss of the different Ni-Zn ferrites were investigated

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with respect to the sintering temperature. The V2O5 and MnCO3 dopants significantly

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improved the initial permeability and power loss characteristics of the Ni-Zn ferrite at

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frequencies ≥ 0.5 MHz. When sintered at 1100°C, sample 2 showed a maximum

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initial permeability of 931.23 H/m at a frequency of 1 MHz combined with a

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minimum power loss of 339.2 kW/m3. Co-doping with V2O5 and MnCO3 also resulted

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in the sintered samples with larger average grain sizes and higher density, while the

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sintering temperature of Ni-Zn ferrites was significantly reduced.

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∗ E-mail: [email protected]; Fax: +86 (0)917-356-6366; Tel: +86 (0)917-356-6055 ∗ E-mail: [email protected]; Fax: +86 (0)917-356-6300; Tel: +86 (0)917-356-6589

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Keywords: Ni-Zn ferrite; Co-doping with V2O5 and MnCO3; initial permeability;

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power loss.

4 1. Introduction

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In recent years, with the trend toward miniaturization and high working

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frequency of electronic equipment, soft ferrite has attracted increasing attention.

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Among them, Ni-Zn ferrite is one of the most important members of the soft ferrite

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family owing to their high electrical resistivity, high initial permeability, and low

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power loss, particularly at high frequencies [1, 2]. The increasing demand for

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miniaturization and high-frequency materials in recent years has spurred the

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development of polycrystalline Ni-Zn ferrite materials for high frequency power

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applications such as broadband transformers, inductors, and high quality filters [3–5].

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Ni-Zn ferrites show significantly higher electrical resistivity compared to their Mn-Zn

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counterparts (by a factor of ca. 102–105), making them the preferred soft magnetic

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material for applications involving frequencies between 1 MHz and hundreds of MHz

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[6]. However, the magnetic properties and microstructure of Ni-Zn ferrites are highly

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sensitive to a number of factors involved in the fabrication process (e.g., sintering

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conditions, preparation method, and nature of the metal oxides including dopants

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and/or impurities). The properties of Ni-Zn ferrites can be greatly affected by the

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addition of dopants in minor amounts [7, 8]. These dopants are mostly added to Ni-Zn

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ferrites to improve their magnetic properties (e.g., increase of the initial permeability,

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reduction of the hysteresis loss, and reduction of the eddy current loss). The most

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common additives are mainly divided into the following groups: (1) additives aimed

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to improve the ferrite microstructure (e.g., CuO and SiO2); (2) additives aimed to

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separate from the grain boundaries and influence the grain boundary resistance of the

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materials (e.g., CaO); and (3) additives dissolved in the spinel structure aimed to

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enhance the magnetic properties of the materials (e.g., Bi2O3) [9–11].

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ACCEPTED MANUSCRIPT Among several additives studied in the literature, V2O5 has considerable effects

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on the magnetic and microstructure of Ni-Zn ferrite [12–14]. These works revealed

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that, when added in appropriate amounts, the additions of V2O5 can significantly

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reduce the sintering temperature and improve the initial permeability of Ni-Zn ferrite.

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However, after the addition of V2O5, the power loss will increase with the increase of

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V2O5 concentration, and the saturation magnetization will decrease with the increase

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of V2O5 concentration [13]. Since high initial permeability and low power losses are

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important for ensuring enhanced performance and quality of soft magnetic ferrites, it

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is difficult to obtain Ni-Zn ferrite materials with both maximum initial permeability

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and the minimum power loss at the same time [15]. Although the doping of V2O5 can

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promote the improvement of the initial permeability of Ni-Zn ferrite, it will also lead

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to the increase of power loss. In order to take into account the characteristics of high

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initial permeability, and low power loss and low sintering temperature at the same

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time, it is necessary to consider the co-doping technology. In recent years, the effect

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of MnCO3 additive on Ni-Zn ferrite magnetism and microstructure has been reported

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[16–18]. These studies revealed that the MnCO3 doping in suitable amounts can

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improve the quality factor (The quality factor is inversely proportional to the core

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loss), initial permeability and magnetization of Ni-Zn ferrites. Therefore, in this study,

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we co-doped V2O5 and MnCO3 additives into Ni-Zn ferrite, and studied the influence

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of different doping amounts and sintering temperatures on the microstructures and

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magnetic properties of Ni-Zn ferrite. A new type of Ni-Zn ferrite material with high

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initial permeability and low power loss was obtained. These results will help to meet

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the requirements of high frequency electronic components. In addition, the study on

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the effect of V2O5 and MnCO3 co-doping on the magnetic properties and

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microstructure of Ni-Zn ferrites has been scarcely covered in the previous literature.

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The present work also fills this gap.

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2. Experimental

ACCEPTED MANUSCRIPT All raw materials employed for fabricating the Ni-Zn ferrite samples (i.e., Fe2O3,

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ZnO, NiO, CuO, V2O5, and MnCO3) were supplied by Aladdin. ZnO, CuO, MnCO3,

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and V2O5 were greater than 99.8% in purity, while the purity of Fe2O3 and NiO was

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higher than 99%. The particle sizes were below 10 µm in all cases. The un-doped

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Ni-Zn ferrite material was composed of Fe2O3 = 65.36, NiO = 10.2, ZnO = 21.14, and

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CuO = 3.3 in wt%. Water was used as a mixing medium, and the oxide powders were

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mixed in a planetary ball mill in adequate amounts for 6 h. After drying, the samples

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were precalcined under air for 2 h at 900°C. Then, the precalcined powders were

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mixed with a varying the loading of the V2O5-MnCO3 dopants (un-doped, 0.4–0.1

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wt%, 0.1–0.4 wt%, 0.2–0.3 wt%, 0.3–0.2 wt%, and 0.5–0.1 wt%, denoted as sample 1,

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sample 2, sample 3, sample 4, sample 5, and sample 6, respectively), and each

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mixture was wet-milled for 10 h in planetary ball mill. The mixture was then dried.

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The resulting particle size of the samples was ca. 2 µm. To facilitate magnetic

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measurements, the calcined powders were first mixed with a 5 wt% poly(vinyl

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alcohol) (PVA) binder and subsequently pressed at 4 ton/cm2 to form toroid with 20

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mm, 9 mm, and 5 mm in outer diameter, inner diameter, and height, respectively.

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Finally, these samples were sintered at 950–1200°C for 2 h.

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The calcined powder samples were characterized by X-ray diffraction (XRD,

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Rigaku, D/max-Ultima IV) using Cu K α radiation (λ = 0.15418 nm). The

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microstructure of the sintered samples was examined by scanning electron

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microscopy (SEM, FEI, Quanta FEG 250). The densities of the toroidal samples were

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measured using a density scale (Sartorius, BSA224S-CW). The initial permeability of

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the toroidal samples was deduced from the inductance measured by a precision LCR

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meter (Keysight, E4980A, 20 Hz to 2 MHz). The power loss values of the toroidal

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samples were measured using a B–H analyzer (IWATSU, SY-8218) at 300 K and 50

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mT. The magnetization at room temperature was measured using a physical property

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measurement system (PPMS) by Quantum Design.

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3. Results and discussion Since high initial permeability is important for ensuring enhanced performance

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and quality of soft magnetic ferrites, we first study this parameter of Ni-Zn ferrites

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with varying amounts of dopants and prepared at different sintering temperatures in

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this study (See Figure S1 of the Supporting Information). It is found that the initial

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permeability of the samples containing additives increases first and then decreases

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with the increase of sintering temperature, and the initial permeability of the samples

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containing additives is greater than that of the samples without additives. This

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indicates that the initial permeability of Ni-Zn ferrite can be significantly improved by

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co-doping of V2O5 and MnCO3. In addition, we observed that the peak value of the

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initial permeability of sample 2 was the largest after co-doping with different loads,

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while the peak value of the initial permeability of sample 3 was the smallest.

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Therefore, in order to accurately study the influence of co-doping and different load

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doping on the microstructure and magnetic properties of Ni-Zn ferrite, in the this

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work, we focus on the microstructure and magnetic properties of undoped sample 1,

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sample 2 with the maximum initial permeability peak and sample 3 with the minimum

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initial permeability peak.

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The XRD patterns of the Ni-Zn ferrite powder samples are shown in Fig. 1. The

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samples showed a single-phase spinel structure within the sensitivity of the

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experimental measurements. Co-doping of V2O5 and MnCO3 did not change the XRD

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patterns significantly, suggesting that the doping loadings were not high enough to

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produce structural changes detectable by XRD. Furthermore, all samples showed

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good crystallization degrees, and the (220), (311), (222), (400), (422), (511), and (440)

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planes were all represented by diffraction peaks, according to the standard XRD

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patterns of Ni-Zn ferrites. The lattice constants of the Ni-Zn ferrite phase were

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estimated as follows [19]:

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= (ℎ +

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(1)

where a is the lattice constant, d is the lattice spacing, and (h k l) are the Miller indices

ACCEPTED MANUSCRIPT of the crystallographic planes. According to the International Center for Diffraction

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Data (ICDD) card number 47-0023, Ni-Zn ferrites have a lattice constant of 8.403 Å.

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Herein, we obtained lower a values for sample 1 (8.399 Å), and this value was also

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lower than that reported for the bulk material [20]. This lower a value of sample 1 can

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be attributed to the following reasons. First, the change of grain size and shape will

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cause a change of lattice constant a, and a decreases with the decreased grain size [19,

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21]. Second, a decreased upon increasing the sintering temperature, since Zn

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evaporates to a larger extent at high temperatures. In addition, the lattice constants a

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of sample 2 and sample 3 obtained by the same method in this study are 8.407 Å and

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8.404 Å, respectively. Therefore, the a values of sample 2 and sample 3 with different

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load doping are very close, and are very similar to the a value corresponding to the

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sample listed in the ICDD card (47-0023).

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Fig. 2 shows SEM micrographs of samples 1, 2, and 3 sintered at different

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temperatures. As clearly shown in Figs. 2(a2), (b2), and (c2), the dopant loading

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affected significantly the microstructure of the samples sintered at 1100°C. For

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example, sample 2 showed an average grain size was about 20 µm, while sample 1

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sintered at the same temperature showed an average grain size as low as ca. 5–6 µm.

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SEM micrographs also revealed that this effect on the microstructure was more

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intense as the sintering temperature increased. The rapid growth in grain size was

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mainly attributed to the generation of a liquid dopant phase, which partially melted at

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high temperature, wetting the grain boundaries. In addition, the grain boundaries

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moved in the direction of the liquid phase under the influence of surface tensions,

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accordingly transforming from a convex surface to a concave surface [22, 23]. By

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comparing the SEM micrographs of sample 2 and sample 3, it can be clearly observed

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that at the same sintering temperature, sample 3 with more additives of V2O5 looks

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denser and has larger grain size. This is consistent with the results reported in

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previous literature [13].

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Figs. 3(a) and (b) show the sintered density and average grain size of samples as

ACCEPTED MANUSCRIPT a function of the sintering temperature, respectively. As shown in Fig. 3(a), the

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density of the sintered samples increased monotonically with the sintering

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temperature. If the samples are to reach the same sintering density, sample 1 need a

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higher sintering temperature than sample 2 and sample 3. This indicates that V2O5 and

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MnCO3 addition significantly reduces the sintering temperature compared with

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undoped Ni-Zn ferrite. This lower sintering temperature may be attributed to the

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formation of a liquid dopant phase during sintering. The liquid dopant phase

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promoted the grain rearrangement and solution-precipitation process, and further

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promoted the densification of Ni-Zn ferrite. As clearly shown in Fig. 3(b), sample 2

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showed higher average grain sizes after sintering at 950–1150°C than sample 3. From

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Fig. 2, we observe that the samples were formed of grains with heterogeneous sizes;

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the average grain size was calculated by averaging the maximum and minimum

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dimension of 40 different grains. After a high-temperature sintering at 1100°C, the

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average grain size of sample 2 was ca. 20 µm, and lower grain sizes were obtained for

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samples 3 (ca. 6.28 µm) and 1 (ca. 5.35 µm). As discussed previously, the magnetic

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properties of Ni-Zn ferrites depend on their microstructure. Among the many

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parameters of microstructure, grain size and porosity are the most important

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parameters that affect the magnetic properties of Ni-Zn ferrites. It is generally

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understood that the following two mechanisms can promote grain growth and

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microstructural changes in Ni-Zn ferrites. First, reduction of the effect of pore

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resistance and impurities on the grain boundary movement. Second, an excess of

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cationic vacancies can increase pore fluidity, which leads to a larger grain growth [23].

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In this study, V2O5 and MnCO3 with low melting point were selected as additives,

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which can form liquid phase and infiltrate grain boundary at low sintering temperature

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to reduce pore resistance during grain boundary movement, thus promoting grain

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growth.

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Fig. 4 shows the power losses of the Ni-Zn ferrite samples studied herein as a function

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of the sintering temperature. The test conditions of power loss of the samples are 300

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ACCEPTED MANUSCRIPT K and 50 mT, and the test frequency is 0.5 MHz and 1 MHz. By comparison with the

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results shown in Fig. 3(a), we can conclude that the power loss decreases with

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increased sintered sample density for sample 2 and sample 3 containing additives. The

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power loss of Ni-Zn ferrites consists of three components namely, hysteresis loss,

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eddy current loss, and residual loss. The eddy current loss dominates the power loss in

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high frequency applications [24, 25]. As shown in Fig. 4, the power loss of samples 2

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and 3 decreased gradually with the sintering temperature up to 1100°C rapidly

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increased thereafter. This could be due to the following reasons. First, after adding a

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trace amount of MnCO3 into the Ni-Zn ferrite, when MnCO3 is sintered in air at high

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temperature, Mn2+ will become Mn3+ with the increase of sintering temperature.

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Through the reaction of formula (2):

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→

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Mn3+ will replace Fe2+ at sites B, resulting in the decrease of Fe2+ concentration in the

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system [16]. With the decrease of Fe ions concentration, the electronics transition

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between Fe3+ and Fe2+ decreases, this leads to an increase in resistivity. Therefore,

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with the increase of temperature, the Fe2+ concentration decreases continuously,

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resulting in the increase of the resistivity of Ni-Zn ferrite. This higher resistivity

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reduces the current generated by the external alternating electric field of the material,

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thus reducing the total power loss [26]. However, when MnCO3 is excessive, excess

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Mn ions will occupy the A sites and make the remaining Fe ions in the original A sites

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move to the B sites, resulting in a greatly increased transition probability between

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Mn3+ and Mn2+. This leads to a reduction in the samples resistivity and ultimately to

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an increase in the total power loss [16]. Second, MnCO3 decomposes into Mn oxides

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in air at high temperature, and Mn oxides can increase the resistivity of intergranular

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region and thus reduce the power loss of samples. As shown in Fig. 4, that the

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minimum power losses of sample 2 were observed after sintering at 1100°C and for

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frequencies of 0.5 and 1 MHz (393.6 and ca. 339.2 kW/m3, respectively). This could

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be attributed to the abnormally high growth of grains at sintering temperatures greater

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ACCEPTED MANUSCRIPT than 1100°C, resulting in higher eddy current losses [26]. It can also be explained that

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when the sintering temperature is greater than 1100°C, the amount of Mn2+ ions

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exceeds that of Mn3+ ions in the reaction system. So Mn2+ ions can occupy A sites and

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force Fe ions to move to the B sites, and the increase of Fe concentration at B sites

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leads to the decrease of resistivity and finally to the increase of power loss. Samples 2

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and 3 showed lower power losses than sample 1, which may be attributed to the fact

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that the dopant increases the material's resistivity within a certain temperature range,

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so that the total power loss of the sample is reduced [16]. In addition, we observed

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that the power loss curves of samples 2 and 3 containing the same kind of additives

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were also different. Although the trend of their changes was to decrease first and then

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increase with the sintering temperature, it was clear that sample 2 had the minimum

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power loss value. This can be attributed to the following two reasons. First, sample 2

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is more densified and the grain size is more uniform. Second, sample 3 contains more

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MnCO3 additives, and a small amount of MnCO3 can reduce the power loss, but

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excessive addition will reduce the resistivity and lead to increased power loss.

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The initial permeability of Ni-Zn ferrite samples as a function of the sintering

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temperature is shown in Fig. 5. Comparing with the results shown in Fig. 3(b), the

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initial permeability was observed to increase with the grain size of the sintered

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samples. As such, the higher initial permeability of the Ni-Zn ferrites after adding

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V2O5 and MnCO3 was expected to be produced by to the higher grain size of these

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samples after sintering. These results were in line with the well-known and significant

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increase of the initial permeability of soft magnetic ferrites with the grain size.

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Comparing the results shown by Figs. 5(a) and (b) indicated that the changes in the

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initial permeability with respect to the sintering temperature were equivalent at test

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frequencies of 0.5 MHz and 1 MHz. In addition, we clearly observed from Figs. 5(a)

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and (b) that the initial permeability followed the trend sample 2 > sample 3 > sample

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1 at different sintering temperatures. Moreover, the initial permeability of samples 2

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and 3 both reached maxima after sintering at 1100°C. The highest initial permeability

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ACCEPTED MANUSCRIPT of sample 2 may be attributed to the suitable doping ratio employed. Thus, optimal

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doping ratios can significantly improve the micromorphology and the average grain

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size of the sample, resulting in optimal magnetic properties. This is also evident from

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supporting information. Finally, as shown in Fig. 5(c), we note that the maximum

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initial permeability of sample 2 at 0.5 MHz and 1 MHz were observed after sintering

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at 1100°C (ca. 875.07 H/m and 931.23 H/m, respectively). This value is higher than

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the initial permeability value of Ni-Zn ferrite reported in recent years [12, 16, 24].

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This may be attributed to the difference in composition. For sintering temperatures

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higher than 1100°C, the initial permeability of samples 2 and 3 decreased sharply,

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which may be attributed to an excessive grain growth under these conditions. The initial permeability and power losses at 1 MHz as well as the densities of the

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samples sintered at different temperatures are summarized in Table 1. By comparing

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the results of Table 1 and those shown in Figs. 4 and 5, we concluded that sample 2

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combined the minimum power loss and the maximum initial permeability after

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sintering at 1100°C. Thus, sample 2 sintered at 1100°C showed optimal magnetic

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properties, making this Ni-Zn ferrite highly suitable for relatively high operating

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frequency applications. In contrast, the power loss of sample 1 increased with the

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sintering temperature, and the initial permeability value was low. These results clearly

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indicated that the judicious addition of V2O5 and MnCO3 not only can improve the

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microstructure of Ni-Zn ferrites, but also can significantly improve the magnetic

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properties of these materials at relatively high frequencies.

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Fig. 6 shows the typical hysteresis loops of the different Ni-Zn ferrite samples at

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300 K. The samples containing additives showed lower magnetization than sample 1.

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For example, the magnetization of sample 1 was 65.01 emu/g at 50 KOe, while those

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of samples 2 and 3 were 64.66 and 63.88 emu/g, respectively. These results revealed

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that the addition of dopants decreased the saturation magnetization (Ms) of the Ni-Zn

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ferrite slightly; this rule is consistent with the results reported in the literature [27].

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Several reasons can explain this behavior. First, non-magnetic ion doping led to lower

ACCEPTED MANUSCRIPT Ms values for the Ni-Zn ferrites, in line with previous reports [28, 29]. Second, this

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lower Ms values can be explained according to the Neel’s model. The net magnetic

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moment of the system is the difference between the magnetic moment of the A and B

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sub-lattices. Thus, since the added V5+ and Mn2+ ions occupy the B sublattice, the

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magnetic moment of the system is reduced [30]. The coercive field (Hc) and remnant

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magnetization (Mr) of the samples also followed this rule, and Hc and Mr decreased

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upon addition of V5+ and Mn2+ ions to the B sublattice. Comparatively, Hc and Mr of

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sample 2 decreased to a lower extent compared to those of sample 3.

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4. Conclusions

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The effects of V2O5 and MnCO3 co-doping on the microstructures and magnetic

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properties of Ni-Zn soft magnetic ferrites were studied as a function of the sintering

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temperature. The results demonstrated that co-doping significantly promoted grain

14

growth and densification of the sintered Ni-Zn ferrites. Thus, the average grain size of

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the doped samples after sintering was as large as ca. 20 µm, approximately 3 to 4

16

times greater than that of the un-doped ferrite. The combined doping of 0.4 wt% V2O5

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and 0.1 wt% MnCO3 increased the sintering density of the Ni-Zn ferrite by ca. 4.7%.

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Co-doping also increased the initial permeability of the Ni-Zn ferrite, reaching

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maximum values after sintering at 1100°C in all cases. In addition, co-doping reduced

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the magnetic power loss obtained over a wide frequency range. Minimum power

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losses were obtained for those doped samples having optimum dopant loadings at

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frequencies of 0.5 MHz and 1 MHz (ca. 393.6 and 339.2 kW/m3, respectively) and

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sintered at 1100°C. These two parameters are much better than general undoped or

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single doped Ni-Zn ferrite. The results obtained herein demonstrated that Ni-Zn

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ferrites co-doped with V2O5 and MnCO3 showed high initial permeability and low

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power loss, characteristics required for high-quality magnetic devices in

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high-frequency applications.

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Acknowledgments

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This work was supported by the National Natural Science Foundations of China

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(21005003), the National-level College Students' Innovative Entrepreneurial Training

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Plan Program (201610721001), the Industrial Science and Technology Plan in

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Shaanxi Province of China (2016GY-226), the Natural Science Foundation of Shaanxi

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Provincial Department of Education (16JF001), the Scientific Research Project of

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Shaanxi Province Office of Education (2018JQ5182), the Young Talent Support

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Program of Shaanxi Province University (20170708), the Doctoral Scientific

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Research Starting Foundation of Baoji University of Arts and Science (ZK2018059).

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Table 1

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Initial permeability (µi) and power loss (Pcv) at a frequency of 1 MHz, and sintered

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density (ρ) for samples sintered at different temperatures. MnCO3

Sintering temperature

(wt%)

(wt%)

(°C)

1

0

0

1

0

1

Pcv (kW/m3)

ρ (g/cm3)

1000

375.4

2450.7

4.76

0

1100

514.6

2745.6

4.93

0

0

1200

657.4

3011.2

5.05

2

0.4

0.1

1000

703.7

2060.6

4.99

2

0.4

0.1

1100

931.2

339.2

5.16

2

0.4

0.1

1200

831.6

3451.8

5.22

3

0.1

0.4

1000

3

0.1

0.4

1100

3

0.1

0.4

1200

5 6 7

13 14 15 16 17 18 19 20 21

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399.9

1593.5

4.98

828.7

2575.3

5.06

473.1

2714.6

5.11

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V2O5

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Graphical Abstract

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Fig. 1. X-ray diffraction patterns for Ni-Zn ferrite powders without doping and with

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different dopant loadings.

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Fig. 2. SEM micrographs: (a1) sample 1 sintered at 1000°C; (a2) sample 1 sintered at

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1100°C; (a3) sample 1 sintered at 1200°C; (b1) sample 2 sintered at 1000°C; (b2)

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sample 2 sintered at 1100°C; (b3) sample 2 sintered at 1200°C; (c1) sample 3 sintered

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at 1000°C; (c2) sample 3 sintered at 1100°C; (c3) sample 3 sintered at 1200°C.

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Fig. 3. (a) sintered density and (b) average grain size of the Ni-Zn ferrites as a

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function of the sintering temperature.

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Fig. 4. Power losses of the Ni-Zn ferrite samples as a function of the sintering

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temperature at frequencies of: (a) 0.5 MHz and (b) 1 MHz. (c) Variation in the power

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loss of sample 2 with respect to the sintering temperature at different frequencies.

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Fig. 5. (a) Variation in the initial permeability of the Ni-Zn ferrite samples with

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respect to the sintering temperature at frequencies of: (a) 0.5 MHz and (b) 1 MHz. (c)

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Variation in the initial permeability of sample 2 with respect to the sintering

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temperature at different frequencies.

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Fig. 6. Typical hysteresis loops of the different samples at 300 K. The illustration in

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Supporting information

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Fig. S1. Variation in the initial permeability of the Ni-Zn ferrite samples with respect

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to the sintering temperature at frequency of 1 MHz.

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