Ferrite Crystals Research Articles

Microwave Conductivity of Single Crystal Mn Ferrites

Microwave Conductivity of Single Crystal Mn Ferrites

Magnons and Phonons in Cobalt Ferrite

Magnons and phonons have been observed in a single crystal of cobalt ferrite, CoFe2O1 at room temperature. Dispersion relations are plotted for the [001] and the [111] directions. The longitudinal acoustic phonon branch has been measured out to the zone boundary in both directions, while the transverse acoustic branch has been completely determined only in the [001] direction. The acoustic magnon branches are well defined at low energies, but they rapidly lose intensity and disappear at around 9 THz. We have not determined uniquely why this happens, but some possibilities are given. Optic branches have been observed at around 11.3 and 14.0 THz. Infrared data indicate that the first branch is probably of phonon character and the second of magnon character.

Electro-magneto-striction effect in a conducting Mn-Zn ferrite crystal

Deformation available to excite ultrasonic vibrations is caused as magnetostriction in a conducting Mn-Zn ferrite crystal when an electric current passes through the crystal. Its conversion efficiency from electrical to mechanical vibrations is very good, because magnetic flux around the current is closed and has no free pole to induce a demagnetization field.

Lattice imaging of the hexagonal ferrites - the M nS series -

Direct lattice imaging techniques are applied to study stacking sequences and sequence faults in hexagonal ferrites of the M nS-type. A similar imaging code as deduced for the M 2Y n-type compounds enables direct recognition of the stacking sequences from the high resolution transmission electron micrographs. Hexagonal ferrite crystals with stacking sequences of the type M, MS, M 2S and M 4S have been investigated.

Fundamental Studies of Cavitation Erosion : In the Case of Low Cavitation Intensity

Previously, the authors reported on the severe erosion where the pit was made by a single blow of cavitation pressure. The present paper deals with the erosion of mild steel under cavitation of comparatively low intensity. Under the test conditions, the incubation period is found in early stage of damage progress, where slips and plastic deformations occur in ferritic crystals but not in pearlitic crystals. From these, the blow intensity of the cavitation is known to be tens of thousands of atm. Cracks are made by the accumulation of plastic deformations and they propagate to a falling off of large particles. Neither residual stresses nor cold worked layers are found in the damaged portions under this progressing stage. This may be one of the characters of erosion under low cavitation intensities.

Flux-Pulling Crystallization of Hexagonal Ferrites with Heterogeneous Seeds

Flux-Pulling Crystallization of Hexagonal Ferrites with Heterogeneous Seeds

The variation of crystal growth rate with supersaturation in fluxed melts

The growth rate of barium strontium niobate and nickel ferrite crystals from borate fluxes was determined by a thermogravimetric method. In the case of the Ba0.5Sr0.5Nb2O6 crystals the growth rate varies as the square of the supersaturation, as predicted by the BCF screw dislocation theory. The data for nickel ferrite shows a linear variation which is believed to be controlled by boundary layer diffusion.

Growth of Strontium Ferrite Crystal from Molten Strontium Borates

The species of crystallizing compounds, its precipitation temperatures and solidus temperature have been determined for the wide composition range of the SrO-B2O3-Fe2O3 system. By cooling the melts of the compositions of the following nominal molar expressions, (1-x)(SrO⋅3B2O3)-xSrO⋅6Fe2O3, (1-x)(SrO⋅2B2O3)-xSrO⋅6B2O3 and (1-x)(SrO⋅B2O3)-xSrO⋅6Fe2O3, Fe2O3 primarily crystallizes in Fe2O3 rich sides. For the serieses of (1-x)(1.5SrO⋅B2O3)-xSrO⋅6Fe2O3, (1-x)(2SrO⋅B2O3)-xSrO⋅6Fe2O3 and (1-x)(3SrO⋅B2O3)-xSrO⋅6Fe2O3, SrO⋅6Fe2O3 crystallizes primarily. Among those the 1.5SrO⋅B2O3 series is best for growth of the crystal, where the x value should be around 0.125.The crystals obtained were hexagonally shaped thin plates; the maximum length of the hexagonal was about 1cm and the thickness was about 3mm. Atomic absorption sepctroscopy revealed that the boron atoms scarecely dissolve in the ferrite lattice (less than 0.02wt% at maximum).It is found that, for the growth of the magnetoplumbite type ferrite crystals from the (nRO⋅B2O3)-(RO⋅6Fe2O3) melts (R=Sr, Ba, Pb), the optimum composition of nRO⋅B2O3 would be a little richer in RO content than that of the glass forming composition of the corresponding RO-B2O3 two component system.

Domain structures in magnetic materials with high crystalline anisotropy

Some of the factors which affect domain structures in magnetic materials with high magnetocrystalline anisotropy include crystal perfection, nonmagnetic or weakly magnetic inclusions, and the nature of grain boundaries. In whisker-like barium ferrite crystals about 3 μm in thickness straight (180°) domain walls were observed in the basal plane. Reverse domains did not nucleate at fields of over -5000 Oe after first saturating the crystals in a positive magnetic field. In less perfect crystal platelets of about the same thickness the domain structures form in what may be described as a convoluted pattern, and after saturating in a positive magnetic field, reverse domains nucleate in positive fields of from +100 to +1000 Oe. An analysis of the convoluted patterns has shown disclination structures of several types. The influence of internal defects as well as the effect of surfaces, nonmagnetic inclusions, and grain boundaries on domain structures in magnetic materials with high crystalline anisotropy are described and discussed.

ANISOTROPY OF Ni2+ AND Ni3+ IONS IN CUBIC SITES

Single crystals of nickel ferrite have been prepared containing (a) F-state Ni3+ ions on B-sites, and (b) F-state Ni2+ ions on A-sites. The ground state triplet levels of both these ions are split by non-cubic components of the crystal field. This splitting can be represented by means of a Spin Hamiltonian which includes the spin-orbit coupling energy and trigonal (or tetragonal) field splitting terms. The contributions to the anisotropy constant K1, due to the two ions, have been determined as a function of temperature and fitted to the parameters of the Hamiltonian by computer. A comparison has been made with the F-state ion Co2+.

Oxygen Diffusion in Nickel Ferrous Ferrite

The diffusion coefficients of oxygen in single crystals of nickel ferrite with Fe/Ni=3.4 were determined as a function of oxygen stoichiometry between 1140° and 1340°C. The diffusion kinetics were followed by measuring the rate of exchange of 18O between the gas and solid slabs of ferrite, and the oxygen stoichiometry was established by controlling total pressure of oxygen in the gas phase. At higher oxygen contents, the diffusion coefficient is independent of stoichiometry and is given by D=10‐2.3exp cm2/s. At low oxygen contents the diffusion rate depends strongly on oxygen stoichiometry and is smaller. In polycrystalline ferrite the diffusion at 1197°C is 40 times faster than in single crystals but shows the same dependence on oxygen stoichiometry. Probable diffusion mechanisms are discussed.

The magnetic domain structures of small crystals

Abstract The first part of the article describes the calculation of magnetostatic energies (which are necessary to predict the critical sizes of crystals below which domains cease to form) and of the domain spacing or number of domains per crystal. Methods suitable for periodic ‘magnetic charge’ distributions in semi-infinite crystals and for finite distributions are described, and both planar and cylindrical domain walls are included. The reasons for the special interest in small crystals is discussed. The second part presents results on thin crystals of barium ferrite with both extensive and discrete structures; orthoferrite crystals with extensive walls and containing one or two cylindrical domains; and small crystals of gadolinium iron garnet near to the compensation temperature, in which the number of domains is a function of temperature. These results are discussed in the light of the theories outlined.

Differential thermal analysis of fluxed melts and its application to the system NiFe2O4-BaO-B2O3

The application of DTA to fluxed melts is discussed, and an apparatus for the determination of the solubility of crystalline materials in molten solutions is described. An exploratory study of the crystallization of nickel ferrite from barium borate fluxes is also described, and solubility curves are presented for fluxes which favour crystal growth. The heat of solution of nickel ferrite was found to be 73 ± 2 Kjoule mole−1.

Preparation of ferrite single crystals by new floating zone technique

Single crystals of Ni ferrites and Ni-Zn ferrites having good uniformity were prepared by a new floating zone technique. In the preparation of the Ni-ferrite single crystal the initial molten zone was made from the material having a composition different from that of seed crystal. This made the composition of precipitate from molten zone the same as that of the seed, and the composition of crystal uniform throughout the entire body. In the apparatus a halogen lamp and the sample were placed, respectively, on the two focal points of a closed elliptical reflector. Under an oxygen pressure of 30 atm, the vaporization of ZnO and the precipitation of another phase in Ni-Zn ferrite single crystals can be almost eliminated.

A simple furnace for the growth of single crystals from fluxed melts under pressure

The construction is described of a simple furnace for fluxed melt growth in oxygen at a pressure of several atmospheres. Results are presented of the application of this furnace to the growth of nickel ferrite crystals containing Ni 3+ ions from borate fluxes of low votality.

合成カルシウムフェライトの鉱物学的ならびに冶金的性状に関する研究

The large perfect crystals of typical calcium ferrites were successfully synthesized by “solid-liquid reaction method” from mixtures correspond to CaO·Fe203, 2CaO·Fe203, Ca0·2Fe203, 4CaO·Fe0·4Fe2O3, 3CaO·Fe0·7Fe203 and 4CaO·Fe0·8Fe203, respectively. The mineralogical properties of synthesized calcium ferrites, i. e., optical characteristics, reflectivity, etching effect, microhardness and Xray diffraction pattern, were examined.Besides Ca0·2Fe203 compound, a ternary calcium ferrite compound proved to exist, whose chemical composition is approximately similar to Ca0·2Fe203 and is estimated to be one of the followings 3CaO·Fe0·7Fe203, 4CaO·Fe0·9Fe203, or 4Ca0·2Fe0·9Fe203. X-ray diffraction patterns of CaO·Fe203, 2CaO·Fe203 and 4CaO·Fe0·4Fe203 were in agreement with the data of previous workers.For determining metallurgical properties of binary calcium ferrites, about 2kg samples are synthesized by solid state reaction. The conventional testing methods for iron ores were applied, i. e., the JIS methods for testing reducibility, the rotation strength after reducibility test, the degradation strength after reduction at lower temperatures, and the temperature of shrinkage, softening and melting. The degradation strength after low temperature reduction of binary calcium ferrites is much higher than that of actual self-fluxed sinter.

Determination of the easy magnetization direction of a ferrite by reflection electron diffraction

Reflection electron diffraction has been used to obtain evidence that the easy magnetization direction of a ferrite crystal of spinel type lies parallel to a <111> direction.

A Magnetically Pulsed Neutron Beam for Time-of-Flight Measurements of Inelastic Scattering

In many types of experiments, time-of-flight neutron spectrometers have the advantage of higher counting rates than crystal spectrometers, especially in view of the fact that multiple counters may be used. A method of magnetically pulsing a neutron beam has been developed that avoids the necessity of using high-speed rotating equipment. The magnetic intensity in a Bragg reflection depends on the orientation of the atomic magnetic moments relative to the scattering vector, and it becomes zero when the moments are directed along the scattering vector. The direction of magnetization in ferrite crystals can be switched rapidly with an external magnetic field so that these crystals can serve both as a neutron monochromator and pulser. Furthermore, the neutron pulse-width and repetition rate can easily be varied by changing the current pulse that produces the external field. The nuclear contribution for the (111) or (331) reflections can be made very small for 7Li-Ti ferrite of the correct composition. Large magnetic scattering intensities can be obtained in each case. The pulsed magnetic field is produced by switching the energy stored in a pulse-forming network into a magnet-drive coil by means of a silicon controlled rectifier. The pulse risetime is about 1 μsec and the pulse length in the present instrument is 12 μsec.

Measurements on Lithium Ferrite Crystals having Near-Zero Defect Concentrations

From a batch of lithium-rich highly ordered single crystals of lithium ferrite, a group of 13 spheres were prepared using regions selected for low defect concentrations. Linewidths measured at 5.1 GHz and ∼300°K ranged from 0.87 to 2.06 Oe with a mean value of 1.35 Oe. The resistivity of the crystals was 3 Ω·cm and 4πMs was 3720±50 G. The narrow linewidths in the presence of such high conductivity suggests a conductivity mechanism other than the usual one involving Fe2+ ions. The sphere with the lowest ΔH was used to measure the temperature dependence of ΔH, ΔHk→0 and HA[111] between 4.2° and 300°K at 10.4 GHz. The ΔH ranged from 1.45 Oe at 300°K to 0.55 Oe at 4.2°K with a peak of 2 Oe near 30°K. At 250°K, ΔHk→0 was 0.4 Oe. It exhibited a peak near 30°K (whose maximum was not measured) and was only 0.06 Oe at 4.2°K. The anisotropy field HA[111] decreased monotonically from 625 G at 4.2°K to 390 G at 300°K. The possession of samples having very small linewidths permitted the study of the effect of ordering on the room-temperature linewidth uncomplicated by other effects.

Croissance des cristaux de ferrite de manganese

We describe a simple method, needing no special devices, which enables single crystals of manganese ferrite of about 1 cm 3 to be obtained, the system remaining macroscopically in the solid state. We use exaggerated growth, induced by barium doping, the percentage of which is set at a defined value, and of which the distribution was rather heterogeneous, to obtain a minimal number of recrystallisation nuclei. This crystal growth process is, in order: a) A very weak solubility of Ba ++ ions in the lattice (55 ppm at 1375 °C) as their radii were very different from that of the sites (Δ r = 0.7Å). b) A formation of a liquid phase at grain boundaries towards which the Ba ++ ions had previously segregated. c) Crystal growth by dissolution-solidification. In spite of a residual porosity, the crystallographic quality of the crystal obtained is good, as was verified by X-ray analysis. The intracrystalline percentage of Ba ++, after slow cooling of the samples, is about thirty ppm.