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Effect of Ca-substitution on the Magnetic and Dielectric Properties of Mn-Zn
Ferrites
中国传说M. M. Rahman1*
doi:
, P. K. Halder1, F. Ahmed1, T. Hossain2, and M. Rahaman2 1Department of Physics, Jahangirnagar University, Savar, Dhaka-1342, Bangladesh 2Institute of Fuel Rearch and Development (IFRD), Bangladesh Council of Scientific and
Industrial Rearch (BCSIR), Dhaka-1000, Bangladesh
Received 7 February 2012, accepted in final revid form 31 March 2012
泰坦尼克号沉没Abstract
Spinel Mn-Zn ferrites with composition Mn x Zn0.4Ca0.6-2x Fe2+x O4,where x= 0.10, 0.15,小鱼汤
0.20, 0.25 and 0.30 have been prepared by conventional ceramic technique sintered at
1300 °C for 4 hours. The influence of Ca-substitution on various properties of Mn-Zn ferrites have been studied in this work. Investigations were carried out by the measurements of Curie temperature, permeability, loss tangent, Q-factor, dielectric constant and AC resistivity of the samples. Curie temperature (T c), the real part of initial permeability (µ´), loss tangent (tan δ), and AC resistivity have been found to be decread while the Q-factor increas with the increa in Ca-content. The frequency characteristics of the dielectric constant and AC resistivity have been found to be decread as the frequency increas.
Maxwell-Wagner interfacial type of dielectric polarization was obrved with the addition of Ca-content over the entire range of frequency considered.
海洋量子号
Keywords: Spinel ferrites; Sintering temperature; Initial permeability; Dielectric constant.
© 2012 JSR Publications. ISSN: 2070-0237 (Print); 2070-0245 (Online). All rights rerved.
dx.doi/10.3329/jsr.v4i2.9752 J. Sci. Res. 4 (2), 297-306 (2012)
1. Introduction
Ferrites constitute a special class of magnetic oxide materials with general formula MO.Fe2O3, where M is a divalent metal ion such as Mn2+, Zn2+, Ni2+, Cu2+, Mg2+, Co2+or Cd2+. The materials show miconducting characteristics which are of great technological applications since they have high electrical resistivity as well as better magnetic qualities [1]. Among the soft magnetic materials for high frequency power electronics Mn-Zn ferrites is one of the most popular and smart candidate of highest rank [2]. The types of polycrystalline spinel ferrites have a wide variety of applications such as power electronics, ferrofluid technology, magnetic data storage, in transformers, choke
坡道定点*Corresponding author:
298 Effect of Ca-substitution
coils, noi filters and as contrast agents in magnetic resonance imaging [3-5]. It is well established that in Mn-Zn ferrites most of the Zn2+ ions occupy in tetrahedral A sites [6] which results in a lowering of Fe3+ in octahedral A-sites. Moreover, structural and other properties of ferrites are dependent on the quality of new materials, milling technique, preparation temperature, concentration of the dopants and impurities [7]. For the reasons, it is possible to introduce various metallic ions to the ferrites to improve their electronic and magnetic properties significantly [8]. In the last couple of decades a very large number of rearches have realized in order to synthesize, to study the properties and to obrve the effect of various additives on their properties [9-32]. Additives play an important role to modify the microstructure and properties of Mn-Zn ferrites generally by three basic mechanisms as mentioned in Ref. [25]. In refs. [26-27] it has been mentioned that Co3+, Gd3+and Eu3+ions replace the metallic cations in tetrahedral A-sites or octahedral B-sites to improve various properties of the samples. Effect of additions of TiO2, vanadium and tungsten on Mn-Zn ferrites have been reported in refs. [29-31]. Addition of CaO in pure Mn-Zn ferrites has been found to reduce the total power loss [32]. However, up until now, as far as we are concerned systematic study about the effect of Ca-substitution on the magnetic and dielectric properties of Mn-Zn ferrites are not available in the literature. For this reason, in this paper we report some systematic investigation on composition, temperature and frequency dependent magnetic, dielectric and electrical properties of Mn-Zn ferrites with the addition of Ca.
2. Experimental Details
Now-a-days different synthesis techniques are ud with various dopants to produce polycrystalline spinel ferrites with enhanced structural, electromagnetic and dielectric properties suitable for magnetic, high-density magneto-optical recording media and microwave applications [33-34]. In the prent work, conventional double sintering technology was ud for the production of Mn-Zn ferrites with Ca as a dopant for its simplicity and availability. The preparation and sintering facility available in the laboratory of Institutes of Fuel Rearch and Development (IFRD), Bangladesh Council of Scientific and Industrial Rearch (BCSIR), Dhaka-1000, Bangladesh has been ud for this purpo. The raw materials Fe2O3, MnO, ZnO and CaO were ud as starting materials. The analytical rearch grade oxides as supplied by the manufacture E. Mark of Germany were ud for the sample preparation process. Appropriate amount of raw metal oxides were mixed, crushed, grinded and milled. Milling was carried out in a wet medium to increa the degree of mixing. To avoid iron contamination, stainless steel balls were ud in a steel ball milling machine and a fluid such as acetone is ud to convert the mixture into slurry. The ground powders were presintered in air or oxygen at 600 0C. Later on, the presintered powders were again crushed into the fine powders. Using die-punch asmbly different shapes of dies were ud to produce the finished prod
ucts. Using the hydraulic press made of nonmagnetic stainless steel, we have prepared two types of samples: cylindrical and toroidal. The finished products were sintered at constant
M. M. Rahman et al. J. Sci. Res. 4 (2), 297-306 (2012) 299
temperature of 1300 0C in air for four hours. A heating and cooling rate of 5 0
C/min was maintained throughout the sintering process.
3. Results and Discussion
Characterization and pha identification of the Mn-Zn samples were performed by X-ray diffraction (XRD) technique. A Philips X’Pert Pro X-ray diffractometer has been ud for this purpo using Cu-K α radiation. XRD pattern of Mn x Zn 0.4Ca 0.6-2x Fe 2+x O 4, where x = 0.00, 0.10, 0.20 and 0.30 has been prented in Fig. 1. XRD patterns confirmed the single-pha cubic spinel structure of the samples without having any other intermediate phas. All the samples have been found to show crystallization, with well-defined diffraction lines. According to the XRD data various diffraction peaks appeared at different planes (111), (220), (311), (222), (400), (422), (511), and (440). It is obrved that all the diffraction peaks are either all odd or all even which indicates the samples are spinel in p
ha . Generally, for the spinel ferrites the peak intensity depends on the concentration of magnetic ions in the lattice. The intensity of the samples has been found to be reduced as the amount of Ca-content is incread.
Curie temperature, T c corresponds to the temperature at which a magnetically ordered material becomes magnetically disordered, i.e., a ferromagnetic or a ferrimagnetic material becomes paramagnetic one. T c of Mn-Zn ferrite samples were determined from
Fig. 1. X-ray diffraction (XRD) pattern of Mn x Zn 0.4Ca 0.6-2x Fe 2+x O 4, where x = 0.00, 0.10, 0.20 and 0.30.
300 Effect of Ca-substitution
the temperature dependence of initial permeability curves. According to Fig. 2, it is obrved that T c decreas with the increa of Ca-content. T c values of Ca-substituted Mn-Zn ferrites have been prented in Table 1. A. Gonchar [35] also reported the similar results. This decrea of T c with Ca-substitution may be attributed to the fact of the weakening of exchange interaction according to Neel’s model. Another earlier study with Cu-substituted cadmium-chromium ferrites [16] also gives support of our findings. It is well known fact that the magnetic characteristics of Mn-Zn ferrites are controlled by the Fe-Fe interaction. Addition of suitable dopant can replace the iron cations which in turn causing the alternation of magnetic behavior of the samples. In ferrites, there are three kinds of i
nteractions between the tetrahedral A-sites and octahedral B-sites: A-A interaction, B-B interaction and A-B interaction [36]. Among the three types of interactions A-B interaction is strongest [36]. Since B-sites have more iron ions than A-sites, addition of Ca ions enters into the A-sites. At the same time, few iron ions are moved into the B-sites, thereby reducing the strength of A-B exchange interaction and hence the T c decreas.
Table 1. Curie temperature of Mn-Zn ferrites with Ca-content.
Composition x Curie temperature, T (°C)
Mn x Zn0.4Ca0.6-2x Fe 2+x O4 0.10 175
0.15 185
0.20 195
0.30 220
Fig. 2. Curie temperature of Mn x Zn0.4Ca0.6-2x
Fe 2+x O4 where, x = 0.10, 0.15, 0.20 and 0.30
with temperature自暴自弃
Fig. 3. Permeability versus frequency curves
of Mn x Zn0.4Ca0.6-2x Fe2+x O4 where, x = 0.10,
0.15, 0.20, 0.25 and 0.30.
M. M. Rahman et al. J. Sci. Res. 4 (2), 297-306 (2012) 301
滑草滑道
Permeability measures the degree of penetration of magnetic field through a magnetic substance. According to the permeability data prented in Fig. 3, it is obrved that the real part of the initial permeability of Mn-Zn ferrites decreas with the addition of Ca. It may be stated that with a small addition of Ca on the Mn-Zn ferrites the density might have been decread which lead to a decrea in permeability. Our result has been found to be in agreement with the previous investigations: ferrites with higher density and larger average grain size poss a high initial permeability and vice versa [37].
Permeability of polycrystalline ferrites is correlated with two types of mechanisms [38-39]. The mechanisms are: domain wall motion and the spin rotational magnetization inside the domains. As the Ca is added to Mn-Zn ferrites calcium iron oxide generates and gregate at the grain boundaries pining at the domain wall. For this reason, domain wall energy is incread and the permeability is decread [40]. The intragranular pores might also be responsible for the pining of the domain walls which results to deterioration of magnetic properties of Mn-Zn ferrites [25]. In our obrvation, it was also obrved that over the entire frequency range the permeability remains almost constant. This might reflect the fact no structural relaxations or resonances are taking place in the obrved frequency spectra.
Figs. 4 and 5 show that the loss tangent of Mn-Zn ferrites with Ca addition as a function of temperature and frequency respectively. The measurements were performed in the temperature range of 25 to 275 0C and over the frequency range from 1 kHz to 500 kHz. According to the data, it is found that the loss tangent of Mn-Zn ferrites decreas gradually with the increa in Ca-content. At lower frequency side around 1 kHz, the loss factor is high but it starts decreasing with the increa in frequency and at high frequency it becomes almost unaffected with the frequency. In ferrites loss tangent, generally, aris Fig. 4. Loss tangent of Mn x Zn0.4Ca0.6-2x Fe2+x O4
where x= 0.10, 0.15, 0.20, and 0.30 as a
function of temperature.
Fig. 5. Loss tangent of Mn x Zn0.4Ca0.6-2x Fe2+x O4
where x = 0.10, 0.15, 0.20, 0.25 and 0.30 as a
function of frequency.
