MnZnFe2O4 soft magnetic composites

Author’s Accepted Manuscript Magnetic properties and loss separation in FeSi/MnZnFe2O4 soft magnetic composites M. Lauda, J. Füzer, P. Kollár, M. Strečková, R. Bureš, J. Kováč, M. Baťková, I. Baťko www.elsevier.com/locate/jmmm

PII: DOI: Reference:

S0304-8853(16)30249-9 http://dx.doi.org/10.1016/j.jmmm.2016.03.051 MAGMA61277

To appear in: Journal of Magnetism and Magnetic Materials Received date: 13 August 2015 Revised date: 19 February 2016 Accepted date: 15 March 2016 Cite this article as: M. Lauda, J. Füzer, P. Kollár, M. Strečková, R. Bureš, J. Kováč, M. Baťková and I. Baťko, Magnetic properties and loss separation in FeSi/MnZnFe2O4 soft magnetic composites, Journal of Magnetism and Magnetic Materials, http://dx.doi.org/10.1016/j.jmmm.2016.03.051 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.

Magnetic properties and loss separation in FeSi/MnZnFe2O4 soft magnetic composites

M. Laudaa, J. Füzera*, P. Kollára, M. Strečkováb, R. Burešb, J. Kováčc, M. Baťkovác, I. Baťkoc

a

Institute of Physics, Faculty of Science, P.J. Šafárik Univesity, Park Angelinum 9, 04154 Košice, Slovakia

b

Institute of Materials Research, Slovak Academy of Sciences, Watsonova 47, 04001 Košice, Slovakia c

Institute of Experimental Physics, Slovak Academy of Sciences, Watsonova 47, 04001 Košice, Slovakia

*

Corresponding author:

Ján Füzer Institute of Physics Faculty of Science Pavol Jozef Šafárik University Park Angelinum 9 041 54 Košice Slovakia tel: +421 55 234 2236 fax: +421 55 622 2124 e-mail: [email protected]

Abstract We investigated composites that have been prepared from FeSi powders covered with MnZnFe2O4 (MnZn ferrite), which was prepared by sol-gel synthesis accompanied with the auto-combustion process. The aim of this paper is to analyze the complex permeability and core losses of prepared samples with different amount of MnZn ferrite. The microstructure and the powder morphology were examined by scanning electron microscopy. Magnetic measurements on bulk samples were carried out using a vibrating sample magnetometer, an impedance analyzer and hysteresisgraphs. The results indicate that the composites with 2.6 wt.% MnZn ferrite show better soft magnetic properties than the composites with about 6 wt.% MnZn ferrite.

Keywords: Powder metallurgy, SEM, Soft magnetic composites, Permeability, Magnetic measurements

1. Introduction Soft magnetic composites (SMCs), which are used in electromagnetic appliances, consist of ferromagnetic powder particles surrounded by an electrical insulating material. These composite materials offer several advantages over traditional laminated soft magnetic materials. They have some unique properties such as three-dimensional isotropic ferromagnetic behavior, lower weight and size, very low eddy current loss, relatively low total core losses at medium and high frequencies, high electrical resistivity and good relative permeability. Soft magnetic composites offer an interesting alternative to traditional materials such as soft magnetic ferrites and electrical steels [1-3]. Several researchers have tried to improve magnetic properties of soft magnetic materials by selecting suitable insulating materials and applying suitable coating methods [4 -6]. Some authors investigated the effect of phosphate modification on the magnetic properties of iron-phenolic soft magnetic composites [7]. A disadvantage of organic coatings, for example silicone and phenolic resin ones, which are widely applied in preparing SMCs, is their limited thermal resistance (almost always

to less than 200°C). Engineering of soft magnetic materials designs materials which posses required electromagnetic properties. Particularly, preparation technology and composition of soft magnetic composite are the most important factors for optimization of both the power loss and the magnetic properties. Therefore a number of different methods are used to prepare SMCs using ferrites (spinel ferrites) as an insulating layer. Spinel ferrites are commonly produced by conventional ceramic processes involving high temperatures, which are above the Currie temperature of Fe-based soft magnetic materials. Other methods for preparation of ferrites involve plasma spraying [8] or sol-gel method [9, 10]. Ferrites have unique magnetic properties such as very high electric resistivity, very low eddy current losses (almost zero) and relatively high magnetic permeability [11-12]. High Curie temperature of spinel ferrites used as insulation between ferromagnetic particles leads to a very high thermal resistance of insulating layers in SMCs. Potential advantage of spinel ferrites when used as electroinsulating layer instead of organic resins is their ferrimagnetic behavior, improving the magnetic interaction between the ferromagnetic powder particles in the final composite. However, because it is very difficult to prepare composites with ferrite insulating layers, only few papers related to this topic were published till now [13-16]. The aim of this work is to describe magnetic properties of a new soft magnetic composite consisting of a commercial FeSi powder, whose particles are covered with MnZn ferrite as an insulating layer.

2. Experimental

Commercial powder consisting of spherical FeSi particles (Höganäs Corporation) with the size from 45 µm to 150 µm was used as a base ferromagnetic material. The chemical composition of FeSi was 97 wt% of Fe, 2.8 wt% of Si, 0.003 wt% of C, 0.04 wt% of O and 0.01 wt% of N. MnZn ferrite prepared by sol-gel synthesis accompanied with the auto-combustion process [17, 18] was used as an electroinsulating layer. Analytically pure chemicals Mn(NO3)2.4H2O (99%, Acros Organic), Zn(NO3)2.4H2O (98%, Acros Organic), Fe(NO3)2 (99%, Acros Organic) and C6H8O7.H2O (99.8% CentralChem) were used to synthesize Mn0.8Zn0.2Fe2O4 ferrite. The process of coating the FeSi

particles was carried out immediately after the gel creation and the autocombustion run [19]. The FeSi particles covered with MnZn ferrite were compacted at 600 MPa to cylindrical and ring shapes and sintered in the laboratory chamber at 780°C in air. We have prepared composite samples with three different amounts of ferrite (2.6 wt%, 5.9 wt% and 6.1 wt%), for each composition two samples under the same conditions, marked as A and B (to compare the reproducibility of the preparation process). The microstructure and morphology of the final composite FeSi/MnZnFe2O4 samples were examined by a JEOL JSM-7000F scanning electron microscope (SEM) equipped with the energy dispersive X-ray analyzer (EDX). The final polishing of samples was done by the focused gallium ions beam (FIB) for 10 minutes (using Zeiss Auriga CrossBeam Compact system with Oxford Instruments 3D EDS X-MAX analyzer). Magnetic force microscopy (MFM) mode measurements were carried out at room temperature using an Agilent 5500 Atomic Force Microscope. The ring samples, with the outer diameter of 24 mm and the inner diameter of 17 mm, were used for magnetic measurements. Specific electrical resistivity was measured by the four-contact method adapted to ring-shaped samples. The real part of the complex permeability spectra was measured by an impedance analyzer (HP4194A) from 30 kHz to 40 MHz. The DC hysteresis loops were measured by a fluxmeter based DC hysteresisgraph. The AC hysteresis loops were measured at the frequency range from 100 Hz to 13 kHz and at maximum induction of 0.1T by two different AC hysteresisgraphs - in the frequency range from 100 Hz to 1 kHz by an AC/DC Permeameter AMH-1KS, and in the frequency range from 1 kHz to 13 kHz by a MATS-2010SA hysteresisgraph.

3. Loss components The most common method of the loss separation in the soft magnetic composite materials is based on the concept that the total losses can be divided into three types, i.e. the hysteresis losses Whyst, the eddy current losses Wed and the excess losses Wexc [20], [

]

The eddy current losses in the composite materials can be divided into two parts. One part (

(1) )

originates from the eddy currents flowing in the entire cross-section of the material and one part

is due to the eddy currents flowing in the interior of a powder particle. The total eddy current losses are determined by the size, shape and electrical resistivity of the specimen and powder particles [21, 22]. Therefore the total losses can be expressed also as [

].

(2)

Hysteresis losses can be obtained directly from the quasi-static hysteresis loop. This part of losses strongly depends on defects, impurities, particle size and internal microstrain introduced during compaction. Excess losses can be calculated by subtracting the hysteresis loss, the intra-particle and the inter-particle eddy current losses from the total losses. Excess losses mostly depend on the size and arrangement of magnetic domains, therefore they are also called eddy current losses caused by the movement of domain walls. For the calculation of the intra-particle

and inter-particle

eddy current losses we have

used known formulas [23, 24] , (

(3)

)

(4)

where Bm is the maximum induction, f is the frequency, dFeSi is the particle diameter, def is the effective dimension for eddy current, ρb is the density of the bulk sample,

is the density of the particle, Rb

is the specific electrical resistivity of the bulk sample and RFeSi is the specific electrical resistivity of the particle. For the ring sample rectangular cross-section [25] perpendicular to the induction the geometrical coefficient β can be expressed as (

,

)

(5)

where w is the width of the rectangle and h its height.

4. Results In the present study we coated spherical FeSi powder particles with MnZn ferrite to electrically insulate the ferromagnetic particles. Insulating material covers FeSi powder particles more or less completely, as indicated by the SEM micrographs, Fig.1, Fig.2.

We prepared several composite FeSi/MnZn ferrite samples with three different amounts of ferrite. Table 1 shows the basic parameters of two samples (A, B) for each composition. Since the two samples containing 5.9% of MnZn ferrite showed quite different magnetic properties, we prepared another two samples with similar ferrite content (6.1%). However, these samples also showed scattered magnetic properties, so we concluded that it is very difficult to prepare samples with higher content of ferrite showing consistent properties. Specific electrical resistivity, hysteresis losses and initial permeability for all samples are shown in the Table 2. All these properties depend on the density, porosity and FeSi content. Total losses WT were calculated directly from the area of AC hysteresis loops. From the area of DC hysteresis loops we obtained hysteresis loos Whyst (Table 2). Intra-particle Wedintra and interparticle Wedinter eddy current losses were calculated from known formulas, Eq.(3) and Eq.(4), respectively, using parameters from Table 3. Excess losses Wexc were calculated by subtracting the hysteresis and eddy current losses from total losses. Fig. 3 shows the hysteresis loop of composite samples with two different amounts of ferrite, indicating soft magnetic properties. The saturated magnetization of FeSi/2.6% MnZn ferrite at magnetic field of 400 kA/m is 169 A.m2/kg and coercivity is 780 A/m. The saturated magnetization of FeSi/5.9% MnZn ferrite at magnetic field of 400kA/m is 160 A.m2/kg and coercivity is 990 A/m. Fig. 4 shows the frequency dependence of the real part of the complex permeability in the frequency range from 30 kHz to 40 MHz. The first type of samples (2.6 wt.% of ferrite) exhibits highest value of initial permeability. On the other hand FeSi/5.9% MnZn ferrite and FeSi/6.1% MnZn ferrite samples exhibit lower values of the initial permeability and of the real part of the complex permeability up to 40 MHz. Higher amount of ferrite has negative influence on the real part of complex permeability. The relaxation frequency was, for all samples, above the upper limit of the impedance bridge, but we assume that the relaxation frequency increases with the ferrite content. The absolute values of the real part of the complex permeability are relatively low, but almost constant up to the frequency of 1 MHz. The total losses as a function of frequency for composite ring samples of FeSi with different amounts of MnZn ferrite measured in the frequency range from 100 Hz to 13 kHz at maximum induction of 0.1 T are depicted in Fig. 5. The total losses of the sample FeSi-6.1% MnZn ferrite A is

almost the same with the total losses of the sample FeSi-5.9% MnZn ferrite A and very different with the total losses of the sample FeSi-6.1%MnZn ferrite B (the sample noted with "A" and "B" are prepared identically). It seems that it is quite difficult to prepare - at least by the method we have used - composite samples with higher ferrite content which would show consistent physical properties. The inter-particle eddy current loss and the excess loss dependence of frequency for all samples are depicted in Fig. 6 and 7, respectively. As we already mentioned the losses in the soft magnetic composites materials can be divided into three types, namely the hysteresis, the eddy current and the excess losses. At low frequencies the hysteresis losses are the main part of total losses and they strongly depend on the particle size, defects, impurities and internal microstrain introduced during compaction. The eddy current losses in composites materials can be separated into two parts. One part originates from the eddy currents flowing in the entire cross-section of the material (Fig.6) and one part is due to the eddy currents flowing in the interior of a powder particle. Inter particle eddy current losses are inverse proportional to the values of specific electrical resistivity of the measured samples (Table 2). They do not influence the total magnetic losses since this part is very low comparing to hysteresis losses and excess losses. Excess losses (Fig.7) result from the eddy currents induced around the moving domain walls. These losses strongly depend on the arrangement of magnetic domains and the demagnetization factor. It is clear from the loss separation that the eddy current losses are very small. The Intraparticle eddy current losses are about 100 times smaller than the total losses and the inter-particle eddy current losses are almost 1000 times smaller than total losses. Very small eddy current losses are caused by high electrical resistivity of all samples. This fact also means that these composites have a very good electro-insulating layer. The first type of samples (2.6 wt% of ferrite) exhibits lowest value of total losses due to the lowest hysteresis and excess losses. In samples with higher amount of ferrite (5.9 wt.% and 6.1 wt.%) higher total losses were observed. Increasing ferrite amount increases hysteresis and excess losses. The domain structure of the FeSi/MnZn ferrite ring samples obtained by FMF imaging is visualized in Fig. 8. It is quite clear from this figure that each FeSi grain has domain structure consisting of several magnetic domains, similar to domain structure of FeSi grains in [26]. The domain structure consists of

about three micrometers wide lamellar domains separated by 180° domain walls. Obviously, the easy magnetization axes of other grains largely deviate from the surface direction and hence probably only branched domain structure can be detected. The surface area of MnZn ferrite between two iron particles exhibits two different orientation of magnetization vector (black and white areas) with different domain structures.

5. Conclusion We successfully synthesized magnetic composite of the FeSi/MnZnFe2O4 type with different amounts of ferrite (2,6 wt.%, 5,9 wt.% and 6,1 wt.%), showing soft magnetic behavior. The magnetic properties of the prepared samples show dependence on their initial composition, porosity and homogeneity. Relatively lower permeability of samples may be attributed mainly to the porosity and internal stresses created by consolidation. On the other hand, porosity increases electrical resistivity and consequently reduces the core losses. It seems that it is quite difficult to prepare - at least by the method we have used - composite samples with higher ferrite content which would show consistent physical properties. Preparation of soft magnetic composites consisting of ferromagnetic particles covered with ferrite, showing very good soft magnetic properties, still remains a challenge.

Acknowledgements This work was realized within the frame of the projects ITMS 2622012001, ITMS 26220220105, which are supported by the Operational Program “Research and Development” financed through European Regional Development Fund. This work was also supported by the Slovak Research and Development Agency under the contract No. APVV-0222-10 MAGCOMP and by the Scientific Grant

Agency of the Ministry of Education, Science, Research and Sport of the Slovak Republic and the Slovak Academy of Sciences, project Nos. 1/0330/15, 1/0377/16.

References [1]

H.

Shokrollahi,

K.

Janghorban,

J.

Mater.

Process.

Technol.,

189

(2007)

1-12.

DOI:10.1016/j.jmatprotec.2007.02.034 [2]

A. Bordianu, O. de la Barriere, O. Bottauscio, M. Chiampi, A. Manzin, IEEE Trans. Magn., 48 (2012) 1537-1540. DOI:10.1109/TMAG.2011.2172927

[3]

H.

Shokrollahi,

K.

Janghorban,

Mater.

Sci.

Eng.

B,

134

(2006)

41-43.

DOI:10.1016/j.mseb.2006.07.015 [4]

B. Ślusarek, B. Jankowski, K. Sokalski, J. Szczyglowski, J. Alloys Compd., 581 (2013) 699704. DOI:10.1016/j.jallcom.2013.07.084

[5]

M. Strečková, L. Medvecký, J. Füzer, P. Kollár, R. Bureš, M. Fáberová, Mater. Lett., 101 (2013) 37- 40. DOI:10.1016/j.matlet.2013.03.067

[6]

A.H. Taghvaei, H. Shokrollahi, K. Janghorban, J. Alloys Compd., 481 (2013) 681-686. DOI:10.1016/j.jallcom.2009.03.074

[7]

M. Huang, C. Wu, Y. Jiang, M. Yan, J. Alloys Compd., 644 (2015) 124-130. DOI:10.1016/j.jallcom.2015.04.201

[8]

Y. Liu, S. Wei, H. Tian, H. Tong, B. Xu, Surf. Coat. Technol., 258 (2014) 189-199. DOI:10.1016/j.surfcoat.2014.09.029

[9]

S. Wu, A. Sun, W. Xu, Q. Zhang, F. Zhai, P. Logan, A. A. Volinsky, J. Magn. Magn. Mater., 324 (2012) 3899-3905. DOI:10.1016/j.jmmm.2012.06.042

[10] S.

Deka,

P.A.

Joy,

Mater.

Chem.

Phys.,

100

(2006)

98-101.

DOI:10.1016/j.matchemphys.2005.12.012 [11]. M. Strečková, H. Hadraba, R. Bureš, M. Fáberová, P. Roupcová, I. Kubena, L. Medvecký, V. Girman, P. Kollár, J. Füzer, E. Čižmár, Surf. Coat. Technol., 270 (2015) 66–76. DOI:10.1016/j.surfcoat.2015.02.054

[12] P. Hu, H.B. Yang, D.A. Pan, H. Wang, J.J. Tian, S.G. Zhang, X.F. Wang, A.A. Volinsky, J. Magn. Magn. Mater., 322 (2010) 173-177. DOI:10.1016/j.jmmm.2009.09.002 [13] Kh. Gheisari, S. Javadpour, H. Shokrollahi, B. Hashemi, J. Magn. Magn. Mater., 320 (2008) 1544-1548. DOI:10.1016/j.jmmm.2008.01.005 [14] J. Moulin, Y. Champion, L.K. Varga, J. M. Greneche, F. Mazaleyrat, IEEE Trans. Magn., 38 (2002) 3015-3017. DOI:10.1109/TMAG.2002.802120 [15] M. Wang, Z. Zan, N. Deng, Z. Zhao, J. Magn. Magn. Mater., 361 (2014) 166-169. DOI.org/10.1016/j.jmmm.2014.02.055 [16] I. Chicinas, T. F. Marinca, B. V. Neamtu, P. Pascuta, V. Pop, J. Therm. Anal. Calorim., 118 (2014) 1269-1275. DOI:10.1007/s10973-014-3961-6 [17] R. Raeisi Shahraki, M. Ebrahimi, S.A. Seyyed Ebrahimi, S. M. Masoudpanah, J. Magn. Magn. Mater., 324 (2012) 3762-3765. DOI:10.1016/j.jmmm.2012.06.020 [18] S.A. Seyyed Ebrahimi, S.M. Masoudpanah, H.Amiri, M.Yousefzadeh, Ceram. Int., 40 (2014) 6713-6718. DOI:10.1016/j.ceramint.2013.11.133 [19] M. Strečková, R. Bureš, M. Fáberová, P. Kurek, P. Roupcová, H. Hadraba, V. Girman, J. Strečka, Adv. Mater. Sci. Eng., 2015 (2015) 1-8. DOI:10.1155/2015/924859 [20] R.M. Bozorth, Ferromagnetism (third ed.), IEEE Press, Piscataway, NJ (1993) [21] C. Appino, O. Bottauscio, O. de la Barriere, F. Fiorillo, A. Manzin, C. Ragusa, IEEE Trans. Magn., 48 (2012) 3470-3473. DOI:10.1109/TMAG.2012.2205670 [22] G. Bertotti, IEEE Trans. Magn., 24 (1988) 621-630. DOI:10.1109/20.43994 [23] A.H. Taghvaei, H. Shokrollahi, K. Janghorban, H. Abiri, Mater. Des., 30 (2009) 3989-3995. DOI:10.1016/j.matdes.2009.05.026 [24] A.H. Taghvaei, A. Ebrahimi, K. Gheisari, K. Janghorban, J. Magn. Magn. Mater., 322 (2010) 808-813. DOI:10.1016/j.jmmm.2009.11.008 [25]

T. D. Shen, U. Harms, R. B. Schwarz, Mater. Sci. Forum, 386–388 (2002) 441–446. DOI: 10.4028/www.scientific.net/MSF.386-388.441

[26] M. Strečková, J. Füzer, L. Kobera, J. Brus, M. Fáberová, R. Bureš, P. Kollár, M. Lauda, Ľ. Medvecký, V. Girman, H. Hadraba, M. Baťková, I. Baťko, Mater. Chem. Phys., 147 (2014) 649-660. DOI:10.1016/j.matchemphys.2014.06.004

Table 1. Basic parameters of prepared samples FeSi-

FeSi-

FeSi-

FeSi-

FeSi-

FeSi-

2.6%

2.6%

5.9%

5.9%

6.1%

6.1%

MnZn

MnZn

MnZn

MnZn

MnZn

MnZn

ferrite A

ferrite B

ferrite A

ferrite B

ferrite A

ferrite B

wt%

2.6

2.6

5.9

5.9

6.1

6.1

External diameter

Φext [mm]

24.27

24.26

24.30

24.28

24.18

24.23

Internal diameter

Φint [mm]

17.92

17.88

17.90

17.90

17.87

17.84

2.39

2.49

2.52

2.62

2.42

2.66

2.990

3.070

3.090

3.185

2.820

3.096

7.59

7.94

8.06

8.36

7.64

8.50

5.95

5.84

5.78

5.76

5.59

5.52

Parameter

Unit

wt% ferrite

[

Height

] [ ]

Mass Cross-section

[

]

[

Density

]

FeSi

[vol.%])

77.3

75.9

72.6

72.2

70.0

69.0

MnZn ferrite

[vol.%]

5.0

5.0

11.2

11.1

11.2

11.0

Porosity

[vol.%]

17.7

19.1

16.2

16.7

18.8

20.0

Table 2. Specific electrical resistivity, initial permeability and hysteresis losses for all samples

Parameter

Electrical resistivity

Unit

[

]

Initial permeability

[ ]

Hysteresis losses

[

]

FeSi-

FeSi-

FeSi-

FeSi-

FeSi-

FeSi-

2.6%

2.6%

5.9%

5.9%

6.1%

6.1%

MnZn

MnZn

MnZn

MnZn

MnZn

MnZn

ferrite A

ferrite B

ferrite A

ferrite B

ferrite A

ferrite B

13.3

14.6

10.8

15.2

29.0

41.0

38.0

36.5

28.4

29.0

24.3

26.2

56.5

56.7

63.2

72.7

62.7

72.1

Table 3. Basic parameters for eddy current losses calculation, where def is the effective dimension for eddy current, β is the geometrical coefficient, ρb is the density of the bulk sample and Rb is the specific electrical resistivity of the bulk sample FeSi-2.6%

FeSi-2.6%

FeSi-5.9%

FeSi-5.9%

FeSi-6.1%

FeSi-6.1%

MnZn

MnZn

MnZn

MnZn

MnZn

MnZn

ferrite A

ferrite B

ferrite A

ferrite B

ferrite A

ferrite B

Figure captions Fig.1. SEM image of FeSi/2.6% MnZn ferrite sample a) cross-section, b) fractured surface, c) the individual FeSi particle covered by MnZn ferrite, with EDX analysis. Fig.2. SEM image of FeSi/6.1% MnZn ferrite sample a) cross-section, b) fractured surface, c) the individual FeSi particle covered MnZn ferrite, with EDX analysis. Fig.3. Hysteresis loop of FeSi/2.6% MnZn ferrite and FeSi/6.1% MnZn ferrite samples with inset showing detailed dependence at low fields. Fig.4. Real part of the complex permeability for samples with three different MnZn ferrite contents, measured at frequency range 30 kHz to 40 MHz. Fig.5. Total losses as a function of frequency for samples FeSi/2.6% MnZn ferrite, FeSi/5.9% MnZn ferrite and FeSi/6.1% MnZn ferrite measured at maximum induction 0.1T in the frequency range 100 Hz to 13 kHz (the sample noted with "A" and "B" are prepared identically). Fig.6. Inter-particle eddy current Losses as a function of frequency for samples with three different MnZn ferrite contents, measured at maximum induction 0.1 T in the frequency range 100 Hz to 13 kHz. Fig.7. Excess losses as a function of frequency for samples with three different MnZn ferrite contents, measured at maximum induction 0.1 T in the frequency range 100 Hz to 13 kHz. Fig.8. Domain structure of the FeSi/2.6% MnZn ferrite composite ring sample.

Highlights 1. Successful preparation of soft magnetic composite FeSi/MnZnFe2O4. 2. Study of the complex magnetic permeability. 3. Comparison of different compositions of prepared SMC’s. 4. Determination of parts of magnetic losses.