Ferrite Single Crystals Research Articles

Ｍｎ‐Ｚｎフェライト大型単結晶量産技術の開発

Kawatetsu Mining Company Ltd. has developed large sized Mn-Zn ferrite single crystals mainly usea as me magnetic heads of the Video Tape Recorder, by innovating the structure of the 3 heater zone vertical Bridgman furnace and by optimizing the growth conditions. The weight of the single crystal is 28 kg, which is 110 mm in diameter and 630 mm in length, approximately 7 times as heavy as those conventionally supplied.Distinctive features of the developed Mn-Zn ferrite single crystal are the uniformity of the composition within +/-0.5 mol%, lower included platinum particles in the crystal and elimination of cracks along with almost the full length of the crystal. In this report, the control of the variation of the composition along with the growth direction, the restriction of the dissolution of the platinum in melt and the suppression of the cracks, which had been main problems to be overcome during the development, are described.

Optical absorption of octahedral ions Fe 2+, Fe 4+ and photoinduced effect in YIG single crystals

The peculiarities of optical absorption of octahedral ions Fe 2+ and Fe 4+ have been analyzed at various parameters of a trigonal and non-trigonal field by taking into account the transitions between levels of a split ground state. The spectral dependence of optical absorption coefficient on parameters of a crystal field has been constructed. The differences of optical absorption spectra that arise with redistribution and change of quantity of ions Fe 2+ and Fe 4+ have been considered. The explanation of experimental results on photoinduced changes of optical absorption in yttrium ferrite garnet single crystals has been proposed.

Temperature effect on the elastic properties of yttrium garnet ferrite Y3Fe5O12

The Young’s moduli along the [100] and [110] crystallographic directions and the shear modulus along the [100] direction in a high-purity yttrium garnet ferrite single crystal are measured in the temperature range from 20 to 600°C. All the independent elastic constants are calculated for this temperature range. The behavior of the elastic moduli and elastic anisotropy factor is analyzed in the vicinity of the critical temperature of the magnetic phase transition.

Analysis of Slip Behavior in Two-Phase (.ALPHA./.GAMMA.) Stainless Steel Bicrystal with Longitudinal Interface in High Cycle Fatigue.

In order to investigate the effect of the constraint of deformation at an interface on the slip behavior, a test is carried out at room temperature in high-cycle fatigue of a two-phase (α/γ) stainless steel bicrystal, which consists of ferritic (Fe30Cr) and austenitic (Fe15Cr15Ni) single crystals, with a longitudinal interface parallel to the load axis. In this bicrystal, the active slip direction intersects the interface. Since the yield stress of α-phase is much higher than that of γ-phase, the slip takes place only in the γ-phase. Not only primary slip lines expected from the crystallographic orientation but also additional slip lines are observed in the γ-phase near the interface. The stress distribution is analyzed by a finite element method (FEM). It shows that the resolved shear stress, τrss, on the specific slip system near the interface increases, and the activated slip system corresponds to the additional slip experimentally observed. The region where the additional slip are observed agrees well with the one where the resolved shear stress exceeds the critical stress of the γ-stainless steel single crystal. This signifies that the characteristic slip behavior near the interface is attributed to the increase of τrss due to the constraint of deformation.

Cyclic deformation of ferritic stainless steel single crystals showing the stress asymmetry

Fe–20%Cr and Fe–30%Cr alloys single crystals having ( 1 ̄ 2 ̄ 3) maximum resolved shear stressed (mrss) plane were cyclically deformed under constant plastic strain amplitudes ε pl of 2.5×10 −3 and 1.5×10 −4. It was found that the tensile stress amplitude was larger than the stress amplitude in compression at the beginning of cyclic deformation. The stress asymmetry was large at higher cyclic frequency and at higher plastic strain amplitude. During cyclic deformation, the stress asymmetry gradually decreased with increasing number of cycles, especially at ε pl=2.5×10 −3. The changes in internal dislocation process are discussed based on a model that attributes the stress asymmetry to the asymmetric behavior of the screw dislocation.

Effect of the domain structure on ferromagnetic resonance in easy-axis ferromagnets

The results of experimental and theoretical investigations of ferromagnetic resonance (FMR) in ferrite single crystals having hexagonal structure and magnetocrystalline anisotropy of the easy-axis type are reported. Experiments are carried out on disk-shaped samples of materials differing in anisotropy strength. The values of the effective anisotropy fields and the gyromagnetic ratios (g-factors) of the materials are determined from measured frequency dependences of the FMR field along the easy and hard magnetization directions for homogeneously magnetized samples. It is shown that if the FMR spectra are also measured for the same samples in the presence of a domain structure, then one can experimentally determine not only the above-mentioned parameters but also the saturation magnetization of uniaxial magnetic materials. It is shown that the theory of the FMR frequency spectrum of a partially magnetized sample with a simple domain structure in the form of a system of plane-parallel layers is in good agreement with the experiment.

Ferrimagnetic resonance of manganese ferrites with iron excess

Ferrimagnetic resonance linewidths of polycrystalline and single crystal manganese ferrites, MnxFe3-xO4 with x<1.0, were measured at 8.9 GHz in the range 77–320 K. Conductivity measurements were carried out from 100 Hz to 40 MHz. The behavior of the ferrimagnetic resonance linewidth and of the resonance field was different from that obtained for manganese ferrites with x=1. These differences are attributed to the presence of a resonance mode in addition to the uniform resonance mode. The variation of the skin depth as a function of the temperature and the high conductivity of the samples is responsible for the appearance of this extra mode. This assumption is corroborated by the analysis of the asymmetry of the absorption curve.

Distortion of a matrix structure and the cluster formation in MnxZnyFezO4 ferrite single crystals

The evolution of the hard and soft modes in the crystal structure of MnxZnyFezO4 manganese-zinc spinel ferrites is investigated theoretically and experimentally (x-ray structure analysis and magnetic measurements). It is shown that tetragonal and rhombohedral distortions of the cubic structure and fluctuations of the soft mode are accompanied by the formation of clusters in the form of quasi-two-dimensional fragments (50–200 and 400–1200 A), which involve families of γ-Mn2O3, γ-Mn3O4, and α-Fe2O3 oxide planes inherently bound to the spinel matrix.

Effect of Interface Boundary on Slip Behavior in the High Cycle Fatigue. Analysis of Slip in Two-Phase (.ALPHA./.GAMMA.) Stainless Steel Bicrystal.

The purpose of the present study is to investigate the unique slip behavior near the interface boundary (IB) in the high cycle fatigue. Push-pull fatigue tests were carried out for two-phase (α/γ) stainless steel bicrystal, which consists of ferritic (Fe 30 Cr) and austenitic (FellCr 19 Ni) single crystals. In the tests, the unique slip, which is not expected from the crystal orientation, was observed in the γ-phase near the IB. The analysis of finite element method reveals that the slip is caused by the increase of resolved shear stress, τrss, due to the constraint of deformation at the IB.

Fine structure and inverse population in the MnKβ1 spectra of MnxZnyFezO4 ferrites

The electronic structure of MnxZnyFezO4 single-crystal ferrites was investigated. The fine structure of their X-ray spectra was found to correlate with the populations of quantum states. A scheme is suggested for the evolution of the electronic structure with strengthening exchange interaction of valence electrons as the chemical composition of the system becomes more complex. The metal-insulator phase transition is possible in the range of compositions corresponding to densities from ρ=5.097 g/cm3 to ρ=5.125 g/cm3, where manganese changes its charge state.

Investigations of nano- and macro-wear of magnetic tape head materials

The nano- and macro-wear characteristics of calcium titanate, single crystal ferrite and polycrystalline ferrite were investigated using nano-scratch testing and wear bar testing. Nano- and micro-indentations were made to determine nano- and micro-hardness, and nano-scratch testing was used to evaluate relative wear rates on the nano-scale. The macro-wear characteristics of the various head materials against metal particle tapes was investigated as a function of tape speed using wear bars mounted in a DLT tape drive. The micro-indentation method was used to investigate wear of the head/tape interface in a linear tape drive. The results from nano- and macro-wear tests were analysed and correlated with the microstructure of the materials.

Nuclear57Fe relaxation in Fe2+-containing NiFe2O4 and CoFe2O4 single crystals

Spin-lattice (T 1) and spin-spin (T 2) relaxation times of 57Fe nuclei in the single-crystal NiFe2O4 and CoFe2O4 ferrites containing Fe2+ ions have been studied in the temperature range of 4.2–100 K by a spin-echo technique. The peaks of relaxation rates T 1 −1 and T 2 −1 caused by the presence of Fe2+ ions were observed for both ferrites in the ranges 38–42 and 28–32 K, respectively. The analysis of the results obtained with invocation of the data on ferromagnetic resonance and the measurements of the temperature dependence of resistivity shows that the mechanism of nuclear relaxation responsible for “impurity” peaks and is a slow relaxation process caused by electron exchange Fe2+ ↔ Fe3+, characterized by a low activation energy.

Surface segregation of antimony on ferritic single crystals

Antimony has frequently been reported to cause temper embrittlement induced by grain boundary segregation in steels containing both nickel and chromium. In order to study the interdependent segregation behaviour of antimony and nickel and the effect of chromium on segregation of these elements, surface segregation was studied on Fe–25% Cr–2%Ni–0.15%Sb and Fe–2.5%Si–2%Ni–0.15%Sb single crystals. Segregation was investigated by means of Auger electron spectroscopy (AES) and low energy electron diffraction (LEED) in the temperature range between 500 and 650°C. On Fe–25%Cr–2%Ni–0.15%Sb, segregation of antimony leading to surface saturation and cosegregation of nickel are observed on (100), (110) and (111) oriented surfaces. LEED investigations yield a complex domain structure which can be derived from a c(2×2) pattern for the (100) oriented surface and a (1×1) pattern for the (111) oriented surface. On the (110) oriented surface, reconstruction occurs. On Fe–2.5%Si–2%Ni–0.15%Sb, the investigated (100) oriented surface is also saturated with segregating antimony. Cosegregation of nickel occurs, but is weaker than on the crystal containing chromium; thus, chromium intensifies cosegregation of nickel with antimony. The LEED pattern exhibits a complex domain structure which is very similar to the structure observed on the (100) oriented surface of the crystal containing chromium.

Depth-selective conversion-electron Mössbauer spectroscopy of the surface of Ba-M hexaferrite single crystals

The magnetic properties of a 50-to 2-nm-thick surface layer in hexagonal ferrite BaFe12O19 single crystals are investigated for the first time. Measurements are made on a conversion-electron Mossbauer spectrometer constructed on the basis of a unique ultrahigh-vacuum magnetostatic electron analyzer of the “orange” type. An analysis of the experimental Mossbauer spectra obtained from the surface layer of BaFe12O19 50-to 2-nm-thick single crystals reveals that (1) the spectral line widths are close to the natural widths of Mossbauer lines and neither changes nor a set of the values of effective magnetic fields, as well as a paramagnetic state of iron ions, could appear due to a defect such as the “surface,” and (2) the experimental spectra are best described only under the assumption that the surface of a hexaferrite BaFe12O19 single crystal contains a 2-nm-thick layer, in which the magnetic moments of iron ions are deflected through ∼20° from the crystallographic C axis along which the magnetic moments of ions located in the bulk of the crystal are oriented.

ＣｏＯ添加フェライト単結晶の磁気特性

A further improvement of high-frequency permeability and loss has been required of ferrite materials in accordance with current trends toward downsizing and higher frequency use.Fe2O3-poor single crystal ferrite that contains CoO was grown by the Bridgeman method for research concerning its high-frequency magnetic characteristics. Single-crystal ferrite with CoO addition showed a significant decrease in high-frequency loss as compared with the conventional crystal ferrite (containing Fe2O3 54 mol %). The permeability was also improved by the addition of CoO at the optimum value.These results were effected by the two factors.1. High resistivity of Fe2O3-poor ferrite results in the reduction of eddy current loss.2. Magnetic anisotropy is changed from negative to positive by the addition of CoO, reducing magnetic anisotropy.

FERROMAGNETIC RESONANCE SPECTRA IN SINGLE-CRYSTAL HEXAGONAL FERRITES

Theoretical and experimental studies of ferromagnetic resonance in single-crystal hexagonal ferrites with different types of magnetocrystalline anisotropy (axis and plane of easy magnetization) are reported. The ferromagnetic resonance is examined in the 12–38 GHz frequency range in the state of homogeneous magnetization and in the presence of a strip domain structure inherent in materials with an axis of easy magnetization. This comprehensive ferromagnetic resonance investigation is shown to allow determination of not only anisotropy fields and g-factors but also saturation magnetization of a material from testing one sample alone. The anisotropy of g-factor of Zn2Y is found experimentally.

磁場配向で作製したＭｎ‐Ｚｎフェライトの磁気特性

Acicular manganese zinc ferrite fine particles were made from the as raw materials of acicular α-FeOOH, Mn(C5H7O2)3, and Zn(C5H7O2)2. These fine particles were oriented with the long axis in parallel to the magnetic flux direction by a magnetic field of 7 kOe. The fine particles were then formed into thin, multi-layered toroidal cores. The green bodies were sintered at 1200°C for 6 hours in air, then cooled in a nitrogen atmosphere. The crystals of sintered manganese zinc ferrites were strongly oriented to the direction of the (110) plane of the spinel; this plane was formed along the upper plane of toroidal cores. The crystal growth behavior was similar to that of a manganese zinc ferrite single crystal of the (110) plane. The initial permeability of crystal-oriented manganese zinc ferrites was 2120. The sample exhibited good high-frequency magnetic properties.

Raman study of substituted barium ferrite single crystals, BaFe12−2xMexCoxO19 (Me=Ir, Ti)

This paper reports the first single-crystal Raman spectra of substituted barium hexaferrites, BaFe12−2x MexCoxO19 (Me=Ir, Ti). The spectra were investigated in the 200–900 cm−1 range and are discussed in comparison with unsubstituted barium hexaferrite. Emphasis was placed on the different factors influencing the Raman spectra of substituted barium hexaferrites, namely the mass of the substituting cation, the ionic radius and charge and the ordering on the five distinct iron sites. Copyright © 1999 John Wiley & Sons, Ltd.

Diffusion Mechanism of Oxide Ions in Mn-Zn-ferrites.

Oxygen self-diffusion coefficients in a manganese zinc ferrous ferrite single crystals were determined at various oxygen partial pressures by means of a secondary ion mass spectrometer. Temperature dependence of diffusivity of oxide ions consisted of three parts. The characteristics at middle temperature range above 5 hPa oxygen partial pressure exhibited a behavior as an extrinsic one and was described as;D=4.8×10-6⋅P0.35O2 exp(-137kJ/mol/RT)cm2⋅s-1This activation energy corresponded to the barrier for the migration of oxide ions in spinel structure. The dependence of oxygen self-diffusion on oxygen partial pressure exhibited a positive sign (slope value: 0.35). This phenomenon suggests that the oxygen ions diffuse in Mn-Zn ferrite through interstitial sites above 5 hPa of the oxygen partial pressure.

シナジー磁石と磁性材料 針状α‐ＦｅＯＯＨを用いたＭｎ‐Ｚｎフェライトの配向性および磁気特性

Crystal oriented manganese zinc ferrites were made from acicular α-FeOOH, Mn(C5H7O2)3 and Zn(C5H7O2)2 as raw materials. The materials were mixed and calcined at 800°C for 4 hours in nitrogen atmosphere. The calcined acicular manganese zinc ferrite fine particles were formed into a thin troidal cores, consist of multi-layered. The green bodies were sintered at the range of 1100 to 1250°C for 4 to 8 hours in air, thereafter cooled in nitrogen atmosphere.The crystals of sintered manganese zinc ferrites were strongly oriented to the direction of {111} plane of the spinel, which was all formed along the upper plane of troidal cores. The behavior of crystal growth was similar to that of manganese zinc ferrite single crystal. The initial permeability of crystal oriented manganese zinc ferrites was 1380 at 0.1MHz and it was not allowed to decay up to 2.2 MHz at the operating condition of the 3dB decrease of the initial permeability. The high crystal orientation and suitable grain size has greatly contributed to the improvement of magnetic properties.