Polycrystalline Mn-Zn Ferrites Research Articles

Preparation and characterization of Mn–Zn ferrites via nano-in-situ composite method

The polycrystalline Mn–Zn ferrites with different iron concentration were prepared by nano-in-situ composite method. The phase composition, microstructure, mechanical and magnetic properties of powders and bulk materials were investigated. The results showed that the crystallinity of powders decreased with the increasing iron concentration from 46 wt.% to 52 wt.%. The single spinel phase was obtained after sintering at 1200°C of all samples. The best comprehensive performance of Mn–Zn ferrite was achieved with the iron concentration 50 wt.%. This manuscript, explained the findings of novel nano-in-situ composite method, which will provoke new thinking and investigation in the research of Mn–Zn ferrite.

Eddy-Current Losses in Mn-Zn Ferrites

We predict the contribution of eddy currents to power losses in polycrystalline Mn-Zn ferrites and apply it to experimental results obtained on a broad frequency range in different commercial materials and differently sized ring samples. It is verified by theory and experiment that the eddy currents can, in sufficiently large specimens, measurably contribute to the energy dissipation, in conjunction with spin damping mechanisms. In this context, the direct role of the domain wall processes is shown to be negligible, with the so-called classical losses, chiefly associated with the rotations, accounting for all of the eddy-current losses. To predict the frequency dependent classical loss W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eddy</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(cl)</sup> (f) in the actual heterogeneous material, the electromagnetic field equations are formulated under a variational multiscale approach, with fine and coarse scales identified with the thickness of grain boundary layers and grain size, respectively. The eddy-current patterns are correspondingly observed to evolve, on increasing the magnetizing frequency, from mostly grain-confined to circulating on the scale of the sample cross-section. Based on the measurement of the electrical resistivity versus frequency and knowledge of the average grain size, an overall frequency dependence of the classical loss W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eddy</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(cl)</sup> (f) is formulated. With the energy loss W(f) measured from dc to 10 MHz in different types of commercial Mn-Zn ferrites having different cross-sectional areas, it is found that the W(f) behaviors in a given material all tend to fall onto a single W(f) curve once purged of the calculated W <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">eddy</sub> <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">(cl)</sup> (f). The residual size-independent loss is the one associated with the damping of the precessional spin motion, which can separately be accounted for.

The effect of substrates on magnetic properties and structure of MnZn ferrite films by alternate deposition

Mn1-xZnxFe2O4 films were prepared by alternative rf-sputtering from targets of MnFe2O4 and ZnFe2O4. The films were deposited on substrates such as single-crystal Si（100）, oxidized single-crystal Si（100）, single-crystal Si（100） with ZnFe2O4 underlayer and single-crystal MgO（100）. The deposited films are amorphous. After annealing in vacuum furnace at 550℃, the polycrystalline Mn-Zn ferrite crystallizes. The film with composition of Mn0.5 Zn0.5 FeO4 shows better magnetic properties: high magnetization Ms and lower coercivity Hc. The coercivity of the film deposited on MgO（100） substrate is the lowest. In this paper, the influences of substrate on film structure and the magnetic properties are investigated. It is believed that the magneto-elastic anisotropy resulting from stress in films dominates the coercivity of Mn-Zn ferrite films. The grain size may be refined to nanometer scale instrumentally by using suitable substrate; the stronger exchange coupling between grains would lead to a lower magneto-elastic anisotropy by averaging to the grains. Therefore, the soft magnetic properties of Mn-Zn ferrite films are improved.

A new Mn–Zn ferrite for high-speed data transmission applications in telecommunication networks

In DSL and ISDN telecommunication technologies, advanced modems are used to increase data transmission speed over regular UTP lines. The good operation of these modems requires a low signal distortion of the polycrystalline Mn–Zn ferrites used as transformer core components at low fields. Given that distortion is directly related to the non-linearity of the B–H loop, the purpose of this study was to determine the basic guidelines for the development of Mn–Zn ferrites with a linear B– H behaviour. It appears that retarding the Fe 2+–Fe 3+ electron exchange with appropriate dopants such as TiO 2 leads to the manufacturing of Mn–Zn ferrite materials that exhibit high initial permeability (∼8500), low losses (tan δ/μ<1.37×10 −6 at 25 °C, 10 kHz, 0.25 mT and tan δ/μ<16×10 −6 at 25 °C, 100 kHz, 0.25 mT) and low hysteresis material constant (<0.17×10 −3), that are suitable for DSL and ISDN transformer applications.

The effect of TiO2 on the magnetic power losses and electrical resistivity of polycrystalline MnZn-ferrites

In this paper the mechanism through which TiO2 affects the magnetic power losses of iron excess polycrystalline MnZn-ferrites is investigated. It has been found that TiO2, on being diluted in the bulk of the grains, promotes the homogeneous accumulation of calcium and silicon along the grain boundaries, by providing high specific resistivity properties to the resulting microstructure. This calcium and silicon segregation enhancement is attributed to the increased cation vacancy concentrations associated with the incorporation of tetravalent Ti in the spinel lattice. The creation of cation vacancies through a dopant such as Ti does not have the same effect as the creation of cation vacancies through control of the partial pressure of oxygen during firing. The latter is believed to promote calcium and silicon accumulation at the pores and the triple points rather than along the grain boundaries, resulting thus in microstructures with reduced specific resistivity.

Conventional and Microcontact Impedance Studies of Mn–Zn Ferrite Ceramics

Microcontact impedance spectroscopy in conjunction with conventional impedance techniques has been performed to elucidate microstructural and compositional inhomogeneities in polycrystalline Mn–Zn ferrites. Microcontact studies reveal the occurrence of oxygen stoichiometry gradients in these typically prepared ferrite ceramics together with a strong spatial resistance variation from boundary to boundary. This leads to a reinterpretation of the conventional impedance spectra of ferrites.

Relation Between Firing Conditions Grain Boundary Structure and Magnetic Properties in Polycrystalline MnZn-Ferrites

The influence of the firing conditions on the nanoscale structure of the grain boundaries and on the magnetic properties of polycrystalline MnZn-ferrites is investigated, on specimens of nearly identical microstructures. High oxygen partial pressures favor accumulation of impurity ions at the triple points. Under appropriate oxygen pressures homogeneous accumulation of impurities along the grain boundaries may occur, revealing therefore chemically pure grains and low hysteresis losses; simultaneously an increase of the grain boundary resistivity occurs that results to low eddy current losses. Managing the raw material impurity cations towards controlled grain boundary structures leads to the synthesis of MnZn-ferrites with power losses similar to those achieved when high purity raw materials are used together with externally introduced additives.

Effect of Rare Earth Substitution on Magnetic and Electrical Properties of Mn-Zn Ferrites

Polycrystalline Mn–Zn ferrites substituted with different rare earth ions (R = La, Nd, Sm, Gd and Dy) are investigated. X-ray diffraction analysis showed a single spinel phase. On substitution, the lattice parameter remained unchanged, the porosity is increased and the grain size is decreased relative to the unsubstituted sample (US). Moreover, on substitution the magnitude of the initial permeability and Curie temperature are decreased. The magnetization, the energy loss and coercive field are decreased for substituted samples, except for R = La where these parameters are increased. The electrical resistivity is found to increase for all substituted samples, except for R = Sm.

Impedance spectroscopic study on the magnetization of polycrystalline MnZn ferrite with very low magnetic anisotropy

Magnetization processes of polycrystalline MnZn ferrite with very low magnetic anisotropy were investigated in the Rayleigh region. Complex permeability spectrum of polycrystalline MnZn ferrite has typically one dispersion. However, two dispersions in complex impedance spectrum from which complex permeability are calculated were observed. Topological and magnetostrictive investigations showed that domain wall motion and domain rotation are responsible for the two dispersions. Calculation of individual contributions of domain wall motion and domain rotation showed that both mechanisms play a significant role in the magnetization process of this material. The role of domain wall in magnetic loss was also discussed.

Self- and impurity cation diffusion in manganese–zinc-ferrite, Mn1−x−yZnxFe2+yO4

Self-diffusion coefficients of Mn, Fe and Zn and the impurity diffusion coefficient of Co in polycrystalline Mn–Zn-ferrite, Mn0.54Zn0.35Fe2.11O4, have been measured by applying the radioactive isotopes 54Mn, 59Fe, 65Zn and 57Co simultaneously. The experiments were conducted at a temperature of 1200°C, as a function of oxygen activity. For comparison purpose, we performed similar diffusion experiments also on Mn-ferrite, MnFe2O4, at the same experimental conditions. We analyzed our tracer diffusion experiments using both the residual activity and the tracer sectioning method. The diffusion coefficients of all the isotopes show a minimum as a function of the oxygen activity indicating that two types of defects, cation vacancies and cation interstitials, contribute to the cation tracer diffusion in both systems. In this paper, we present the experimental results and a defect chemical analysis of Mn–Zn-ferrite to discuss the influence of the Zn-content on the cation diffusion in Mn–Zn-ferrite.

Electrical transport properties of zinc-substituted manganese ferrites

Electrical transport properties such as electrical conductivity (σ) and thermoelectric power (S) of polycrystalline Mn–Zn ferrites of various compositions have been investigated as a function of composition and temperature. Plots of log(σT) versus 103/T are increases with the increase of temperature and show transition near Curie temperature. The activation energy in the ferrimagnetic region is in general less than that in the paramagnetic region. The carrier concentration and mobility of charge carriers has been computed from values of electrical conductivity and Seebeck coefficient. An attempt is made to explain the conduction mechanism in these ferrites.

Magnetic Transitions Studied by Electrically Based Methods in Mn-Zn Ferrite

ABSTRACTThe thermal variations in electrical conductivity of polycrystalline Mn-Zn ferrites was investigated by impedance spectroscopy. Two well defined semicircles were observed in complex impedance plots, which were associated with grain (or bulk) and grain boundary impedance response, for the high and low frequency ranges, respectively. From these results, the characteristic relaxation frequencies were obtained for each process. The grain boundary frequency exhibited a monotonous behavior as a function of temperature, while the bulk frequency showed a maximum at 132 °C. By a magnetic method, it was verified that this temperature corresponds to the Curie transition. These results show therefore that a magnetic phase transition can be studied by means of electrical methds.

Microtribological studies of Al 2O 3, Al 2O 3TiC, polycrystalline and single-crystal MnZn ferrite, and SiC head slider materials

Surface topography, friction, scratching, wear and nanoindentation behavior of head slider materials were studied using atomic force/ friction force microscopy (AFM/FFM). Materials studied include polycrystalline Al 2O 3, Al 2O 3TiC (70-30 wt.%), polycrystalline MnZn ferrite, single-crystal MnZn ferrite and polycrystalline SiC. Al 2O 3 is not used for construction of head slider but it was studied for comparisons with Al 2O 3TiC. SiC is a candidate slider material. The Al 2O 3TiC specimen exhibits the highest coefficient of microscale friction followed by polycrystalline MnZn ferrite, Al 2O 3, single-crystal Mn ferrite, Al 2O 3, single-crystal MnZn ferrite and SiC. Two phase Al 2O 3TiC exhibited higher microscale friction than a single phase Al 2O 3 and polycrystalline MnZn ferrite exhibits microscale friction than a single-crystal MnZn ferrite. The local variation in friction force for Al 2O 3, polycrystalline and single-crystal MnZn ferrite was found to correspond to the lcoal surface slope (first derivative of the surface roughness profile). For Al 2O 3TiC and SiC specimen, the local variation in friction force at the scratches corresponds to the local surface slope. However, local variation over entire region corresponds to the different phases present on the specimen surface. Thus friction force imaging can be used for structural mapping of the surfaces. Directionality effects in the friction were studied on a microscale for the Al 2O 3 specimen. Macroscale friction values for all samples are higher than microscale friction values as there is less ploughing contribution in microscale friction measurements. Microscratching/wear studies indicate that scratch and wear resistance of SiC and Al 2O 3 are higher than that of the other specimens. However, Al 2O 3 specimen shows the presence of porous holes on the surface that affect the wear performance. Al 2O 3 specimen exhibits superior microscratch and microwear resistance than Al 2O 3TiC. Wear evolution for single and two phase materials was studied in detail. Nonoindentation hardness values found to be generally higher than that of microhardness data. Based on these measurements, coefficient of friction, microscratch and microwear resistance of singe phase materials are superior to that of two phase materials.

Experimental Evidence for Harper–Dorn Creep in Mn–Zn Ferrite

Creep data on polycrystalline Mn–Zn ferrite are presented to show the operation of Harper–Dorn creep at low stress and large grain size. The main evidence for this suggestion is that under these conditions Newtonian creep does not depend on the grain size of specimens, and the observed strain rates are a few orders of magnitude faster than those predicted by diffusional creep. Deformation mechanism maps constructed for Mn–Zn ferrite show that the deformation of this material may be controlled by Harper–Dorn creep over a wide range of temperature and grain size at low stresses.

Spin-phonon coupling in MnŹn ferrites

Ultrasonic attenuation and dispersion are studied in polycrystalline MnZn ferrites. Both factors are strongly influenced by the coupling of sound waves to the spin system. This coupling is governed by the λ 111 magnetostriction constant only, and not by λ 100. A simple model can account for all the observed results in a quantitative fashion. Using this model, values of λ 111 can be determined from acoustic and susceptibility measurements which show good agreement with λ 111 data from the literature on static torque measurements of single crystals.

Effect of heat treatment on the microstructure and magnetic properties of polycrystalline MnZn ferrites

The effect of heat treatment of commercially available polycrystalline MnZn ferrite slabs was studied for temperatures near typical recording head glassing temperatures. Toroid-shaped specimens were heated in atmospheres of varying levels of oxygen and the deterioration in magnetic properties was measured. The surfaces of the exposed specimens were inspected by means of optical and electron microscopy and the occurrence of ferrite instabilities such as grain growth, segregation of secondary phases etc. were observed. The degradation also appeared to be surface-driven. To investigate this further, some samples were heat treated in highly oxidizing and reducing atmospheres to induce gross ferrite instabilities. The near surface regions of these samples were then characterized by x-ray diffraction, x-ray photoelectron spectroscopy (XPS) and conversion electron and conversion x-ray Mossbauer spectroscopy (CEMS and CXMS). In addition to grain growth and other structural changes, the precipitation of extraneous phases appears to be a major mode of ferrite failure during such annealing.< <ETX xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">&gt;</ETX>

The initial permeability of polycrystalline MnZn ferrites: The influence of domain and microstructure

The validity of nonmagnetic grain-boundary (NMGB) models for the initial permeability of polycrystalline ferrites is examined. The domain size in a series of wet-chemically prepared polycrystalline MnZn ferrites, in the demagnetized state, has been determined by neutron depolarization. A transition in the intragranular domain structure from mono- to two domain is observed at grain size D≊4 μm. An expression for this transition has been derived for a dense magnetic material. The grain size dependence of the initial permeability of the ferrites studied, particularly for monodomain grains, is consistent with the NMGB model. The grain-boundary width and composition have been determined with a nanoprobe (1.5 nm resolution). Composition variations extend ≊10 nm into the grain. The findings suggest that, although the NMGB model considers ‘‘nonmagnetic’’ grain boundaries, in practice the grain boundary may be hard magnetic.

Ｏ２‐ＨＩＰによるＭｎ‐Ｚｎフェライトの高密度化

This study aims to densify sintered polycrystalline Mn-Zn ferrites, using O2-HIP treatment in Ar atmosphere containing 0.1 % O2. It is expected that this treatment enables to economize use of packing ferrite powders or annealing process as in Ar-HIP treatment. After HIP treatment of 49 MPa at 1200°C for 1 hr, the HIPed ferrite reaches almost theoretical density. Its permeability at 100 kHz decreases from 3600 to 2500, while the loss factor, tan δ/μ, decreases to less than half.

MIG mini composite head using single crystal Mn-Zn ferrite

Metal-in-gap (MIG) miniature composite heads whose magnetic circuit is composed of single-crystal Mn-Zn ferrite and sputtered Fe-Al-Si film were prepared. Recording and readback characteristics are compared with those of MIG heads using polycrystalline Mn-Zn ferrite. The relationship between timing asymmetry and bit shift is discussed. Results of magnetic-domain observation by SPIN SEM (scanning electron microscopy) are presented. The output voltage of the single-crystal ferrite MIG head showed a 35% higher value than that of ordinary polycrystalline ferrite. This result is due to the higher readback efficiency, arising from higher permeability of the stressed ferrite. Bit shifts of single-crystal MIG heads are small because of their small timing asymmetry and sharp distribution. Timing asymmetry fluctuations are thought to be due to Barkhausen-like domain-wall pinning through readback. This phenomenon is much less significant in single-crystal ferrites; hence, MIG heads are more suitable for high-density recording than polycrystalline ferrite heads. >

Rubbing noise generated by acoustic vibrations in ferrite test heads

Rubbing noise (RN) is an effect whereby acoustic waves generated by the friction between the head and the recording tape cause flux changes to circulate through the head, inducing a noise voltage over the windings of the head. T. Kimura et al. (1980) have demonstrated the correlation between RN peak frequencies and sample dimensions in special test heads made predominantly from polycrystalline MnZn ferrite. The present authors have expanded on the experiments by investigating similar test heads of single crystal material and identifying several distinct acoustic vibrational modes and corresponding propagation velocities. The most important features of the spectra are: (1) strong peaks appear in the RN spectra at certain frequencies; (2) as the tape velocity is increased, the amplitude of the RN increases, but the frequency distribution is unaltered; (3) when the yoke height is reduced by lapping, the peaks in the frequency spectra shift systematically to higher frequencies; (4) one longitudinal and two transverse velocities are required to explain the observed frequency shifts for yoke heights >340 mu m; (5) for smaller yoke heights, modes of lower propagation velocities are found. >