New magnetic materials derived from chromium dioxide

A new oxidative method of preparation of the chromium dioxide from Cr2O3is described. For the improvement of magnetic properties, in particular coercive field, of such a ferromagnetic oxide a substitution by rhodium +IV leads to the new interesting material Cr1-xRhxO2with needlike particles (H_{c} simeq 500Oe).     

Particle flow and collection process in single wire HGMS studies

A television system for the observation of HGMS particle flow and buildup on a ferromagnetic wire or small array of wires is described for three geometries. Data for the collection process and a sequence of pictures of buildup are presented for Mn2P2O7, Mn2O3, and Cr2O3particles collected on 125 μm nickel wires. The wake, formed in some cases downstream from the particle collection, has been studied. Data on the wake is given and compared with published data on wake formation. New results on downstream and upstream collection on a wire as a function of slurry velocity is presented.     

A new permanent magnet material: Modified Ca ferrite

An experiment was carried out to investigate the preparation condition of anisotropic Ca system ferrite magnets with optimum magnetic and physical properties. Compositions were chosen according to the formula (CaO.nFe2O3)100-x(La2O3)x, wherexwas varied between 0 and 4.0, and n between 5.5 and 6.25. The optimum condition of making magnets and some properties of a typical specimen are as follows. The preparation condition: composition (CaO.6Fe2O3)97(La2O3)3, semisintering condition 1250°C × 1 h in O2gas, sintering condition 1275°C × 0.5 h in O2gas. Magnetic properties:4piI_{10}k = 4200G, 4πIr = 4100 G,IHC= 2100 Oe,BHC= 2050 Oe,(BH)_{max} = 3.5MG . Oe, Ku = 3.34 × 10⁶erg/cc, HA= 20.5 kOe,sigma_{s} = 64.8emu/g, Tc = 446°C.     

Crystallographic and magnetic investigation on W-type-hexaferrite single crystals in the solid solution series SrZn2-xCoxFe16O27

The saturation magnetization and the magnetocrystalline anisotropy were measured on single crystals in the solid solution series SrZn2-xCoxFe16O27(SrZn2-xCox-W) at 298 K and 6 K. Lattice constants and Curie-temperatures are also given as a function of the composition. The magnetocrystalline anisotropy changes from uniaxial to planar dependent on temperature and cobalt substitution atx approx 0.5for 6 K andx approx 0.85for 298 K. The six-fold anisotropy in the basal plane of the planar W-hexaferrites increases strongly with increasing cobalt content. Crystals with a low Co substitution (x = 0.33 and 0.67) have an anomalous discontinuity in their hard direction magnetization curves; indicating a first-order magnetization process.     

Influence of R1parameter {=Fe2O3/(Y2O3+ Sm2O3+ Lu2O3)} on magnetic bubble properties of (YSmLuCa)3(FeGe)5O12

The influence of R1{=Fe2O3/(Y2O3+Sm2O3+Lu2O3)} in the melt composition on film properties, and growth characteristics, has been investigated for (YSmLuCa)3(FeGe)5O12. The garnet phase is the primary phase when R1is kept between 10 and 60. The temperature coefficient for the bubble collapse filed changes from -0.29 to -0.19 %/°C, and the growth rate with 10°C supercooling changes from 0.60 to 0.15 μm/min, by increasing R1=10 to 60. Distribution coefficients, K^Y, K^Sm, K^Luand K^Geincrease, and K^Feand K^Cadecrease, with increasing R1.     

Preparation of M- and W-type hexaferrite particles by the glass crystalization method on the basis of the pseudo-ternary system Fe2O3- BaO - B2O3

The preparation of M- and W-type Ba-hexaferrite particles by the glass crystallization method was investigated. For this purpose that part of the pseudoternary phase diagram Fe2O3-BaO-B2O3was elaborated in which primary crystallization of BaFe12O19occurs. This three-dimensional region was found to be located within the triangle Fe2O3-BaB2O4-BaFeO2,5. The lowest temperature of primary crystallization of BaFe12O19is close to 800°C near the composition 55 mol% BaO, 20 mol% B2O3and 25 mol% Fe2O3. Using the knowledge of that system it was also possible to synthesize W-type Ba-hexaferrite particles (BaZn2Fe16O27) by the glass crystallization method. Magnetic data of M- and W-type hexaferrite pigments prepared by that method are given. Particle size from a tenth of a micron to more than ten microns was obtained.     

Magnetic properties of new manganese ferrites submicron particles

New manganese defect metastable ferrites with spinal structure were prepared by oxidation at a temperature lower than 500°C of submicron manganese substituted magnetites, Fe3-xMNxO4(0 leq x < 1). X-ray diffraction measurements and thermal analysis studies have been carried out on these systems. Low-temperature magnetic measurements have also been carried out. With these studies, it has been possible to depict the cation distribution in substituted magnetites and oxidized compounds, and to understand the complex process of oxidation. In defect spinels, vacancies are formed not only from oxidation of Fe²⁺ions, but also of Mn²⁺and Mn³⁺ions. Manganese-rich compound with x = 0.97 having high content of Mn³⁺and Mn⁴⁺ions show an important increase in coercive force, which exceeds 700 Oe at 4.2 K.     

Pressure-induced signal loss in Fe3O4and γ-Fe2O3thin film disks

Pressure-induced signal loss in Fe3O4and γ-Fe2O3thin film disks has been investigated. Through gauzes, pressure of 20 to 500 g/cm²were applied to the surface of a disk rotating 300 revolutions per minute (rpm). The result was extremely large signal losses of 40 to 90 percent. Several types of losses characteristic of ferrite surfaces were observed: initial loss, subsequent loss, and steady loss. These phenomena were consistently explained by a model that shows that the removal of a small amount of unstable surface crystallites by pressure reduces the leakage flux density. Wiping the rotating disk surface with gauze at a pressure of about 1000 g/cm²was effective in reducing the loss. It was confirmed that Ti doped γ-Fe2O3thin films prepared from α-Fe2O3show better resistance to pressure than do Fe3O4and other γ-Fe2O3films. Surface lubrication of the medium was also confirmed to be effective in reducing the loss. Contact-start-stop (CSS) induced signal loss and the possibility of pressure-induced missing signal errors due to thin film pinholes were also examined for typical γ-Fe2O3thin film disks.     

Magneto-optic insulators utilizing the optical activity of Co++(Td)

Large magneto-optic effects are associated with the crystal field transitions of Co++(Td) in a variety of spinel oxides. In the oxides, the F and P crystal field bands peak at about 1.5 and 0.6 μm, respectively. Many iron-containing quaternary compounds (CoTxFe2-xO4) have transition temperatures above ambient. Here, T is a trivalent metal ion such as Cr³⁺or Rh³⁺. Room-temperature magneto-optic measurements on a number of these compounds indicate peak Faraday effects in the range of 0.5 × 10⁵to 1.0 × 10⁵(deg/cm) at about 0.6 μm. The Curie temperature may be adjusted by the compositional parameter x and normal remanence of the surface Kerr effects are observed. The latter properties are potentially useful for optical memory devices. These materials are considered for isolation and modulation devices in the 5.0 to 12.0 μm wavelength range.     

High gradient magnetic separation: Theory versus experiment

The experimental performance of a high gradient magnetic separator has been previously reported by other workers in some detail for a CuO/Al2O3slurry. Less detailed results were also reported for slurries of Mn2O3, Al, and α-Fe2O3particles with Al2O3representing a 20:1 range in particle sizes and a 200:1 range in magnetic susceptibility. Examination of these results indicates that many layers of particles build up on each filter fiber. Accordingly, in this paper we extend the original particle trajectory model for the calculation of filter performance, to include the build-up of multiple layers of particles on the fibers. Good agreement is obtained between the calculated recoveries and purities for all of the particles and the experimentally reported values using a filter packing efficiency and a mechanical trapping term, derived from the CuO data, as adjustable parameters.     

Tb1-xDyxFe2-y-BaTi0.99Mn0.01O3+δ层状复合材料的低频磁电耦合

利用弹性力学模型,推导了低频下磁致伸缩-压电双层复合材料中磁电电压系数的表达式,计算了Tb_1-x Dy_x-Fe_2-y-BaTiO₃层状复合材料中的横向磁电耦合。采用溶胶-凝胶法制备1.0%（摩尔分数）Mn掺杂BaTiO₃（BaTi_0.99Mn_0.01O_3+δ）压电陶瓷片。将Mn掺杂BaTiO₃与Tb_1-xDy_xFe_2-y 胶合制成双层和三层复合材料,研究了复合材料在低频下的横向磁电效应。XRD和DSC分析结果表明,室温下Mn掺杂BaTiO₃保持了其四方钙钛矿结构,降低了BaTiO₃的居里点和相变潜热。在约33 kA/m偏置磁场下,Tb_1-xDy_xFe_2-y-BaTi_0.99Mn_0.01O_3+δ 和Tb_1-xDy_xFe_2-y-BaTi_0.99Mn_0.01O_3+δ-Tb_1-xDy_xFe_2-y 的横向磁电耦合峰值分别为529.4 mV/A和1659.5 mV/A,分别是Tb_1-xDy_xFe_2-y-BaTiO₃和Tb_1-xDy_xFe_2-y-BaTiO₃-Tb_1-xDy_xFe_2-y 的1.48和1.45倍。三层复合材料的横向磁电电压系数约是同类双层的3倍多。     

Origin of coercivity changes during the oxidation of Fe3O4to γ-Fe2O3

Oxidation kinetics and x-ray diffraction of the intermediate products have been investigated for several kinds of Fe3O4powders during the oxidation to γFe2O3. From these results, a two-components-hypothesis as an intermediate state of the Fe3O4- γFe2O3system is proposed, instead of a homogenious solid solution which has been widely recognized. The effect of the changes in particle size caused by the two phases oxidation products on the variations of magnetic coercivity was emphasised.     

On the microstructure and magnetization process of γ-Fe2O3

Experimental evidence is reported for γ-Fe2O3single particles being made up of several microcrystals chained together and their boundaries being sources of demagnetizing fields. This leads to a very defined picture of the magnetization reversal in partially alligned γ-Fe2O3particles: rotation is incoherent but the magnetization vectors are scattered in such a way that Hcivs. angle Ψ (between the orientation direction and the applied field) does not follow the known magnetization reversal modes. The importance of the reduction temperature in the process: α-FeOOHunderrightarrow{red.}Fe3O4underrightarrow{ox.}γ-Fe2O3becomes extremely important if considered as the parameter which rules the pore closure within the particles, i.e. the size and number of microcrystals chained in a single particle.     

The effect of melt composition on the curie temperature and flux spin-off from lutetium containing LPE garnet films

The effect of the melt PbO/B2O3ratio on the Curie temperature of LPE films containing lutetium is described along with data showing the flux effect on the bubble collapse field temperature dependence. A mechanism is proposed to explain the observed data involving the complexing of the rare-earth ions in the melt by B2O3. A correlation is shown between the Curie temperature and lattice parameter of lutetium containing LPE films where certain of the important melt ratios are held constant. The variation of Curie temperature with changing growth temperature is also described. The previously observed Curie temperature dependence on the Fe2O3/Lu2O3ratio is confirmed over a wider range of iron to lutetium ratios. The effect of changing the PbO/B2O3ratio and its effect on flux removal is presented.     

Grain-size dependence of anhysteresis in iron oxide micropowders

The low-field anhysteresis of small equidimensional multidomain particles of Fe3O4is found to be surprisingly large. For particle sizes below about 0.075 μm the anhysteretic susceptibility equals or surpasses that of elongated or doped equidimensional single-domain γFe2O3particles used in conventional recording tapes.     

Growth and properties of garnet films for storage application

A discussion of the growth of garnet films by liquid phase epitaxy without rotation of the substrate is presented for magnetic garnet layers used as materials for bubble [(YSm)3(FeGa)5O12; (YLa)3(FeGa)5O12] and magneto-optical memories [(GdBi)3(FeGaAl)5O12]. The background of the experimental and compositional approach is given.     

High-field magnetism in non-polar γ-Fe2O3recording particles

Fine γ-Fe2O3particles produced by a process which involves hydrothermal conversion of iron hydroxides to α-Fe2O3have been investigated. Such particles appear to lack pores or dentrites which cause internal magnetic poles, and exhibit superior properties for magnetic recording. Mössbauer spectroscopy, x-ray diffraction, and transmission electron-microscopy were used. The particles were of length 250-500 nm and width 35-50 nm; some samples had cobalt adsorbed onto the surface. Mössbauer spectra were collected at temperatures from 4.2 to 300 K, and in zero and 5 T applied magnetic fields. In general the patterns are typical of bulk γ-Fe2O3. The 300 K spectra of Co-doped samples show sub-patterns of weak intensity associated with at least two distinct additional components with reduced splitting. One of these has Bhf= 45.2(2) T; its origin is suggested to be iron-atoms lying in or close to the cobalt-modified surface. In a 5 T field, the iron-atom moments deviate from the applied field direction by average angles in the range 13-15°. Because the angle for conventional similarly sized γ-Fe2O3issim 13deg, it is concluded that the improved particle morphology does not lead to an improvement in the high-field alignment.     

Magnetostriction in some magnetic oxide compacted powders

Magnetostriction measurements have been made on a series of compacted powder samples of oxide pigments used in magnetic recording, to provide information for the evaluation of the role of magnetostriction in the recording process. Two composition series were measured at 294 K: one from γFe2O3through a range of partial reductions to Fe3O4, and another from 0 to 4 at. % Co in γFe2O3; also samples of CrO2. In addition, a 2 at. % Co-doped Fe3O4powder was measured as a function of field and temperature from 77 to 300 K. Magnetostriction was measured using a semiconductor strain gage on a rotating sample, in fields up to 9 kOe.     

Magnetic interactions in pseudobinary rare earth-3d intermetallics

Magnetic measurements on pseudobinary intermetallic compounds of the series R(MnxFe1-x)2(R = Y, Gd, Er) R6(MnxFe1-x)23(R = Y, Gd, Tb, Dy, Ho, Er, Tm) R2(FexCo1-x)17(R = Y, Gd, Dy) R2(FexNi1-x)17(R = Y, Gd) are reported. Magnetization and susceptibility measurements have been performed at temperatures from 4 K to 1500 K. The magnetic interactions between Mn and Fe are discussed in terms of a localized-moment model. In the case of the R2(FexM1-x)17(M = Co, Ni) compounds, a band model seems to be more appropriate. Mössbauer Fe⁵⁷spectra obtained on the R2(Fe,Co)17series can be explained by a superposition of four different six-line patterns corresponding to the four crystallographically nonequivalent 3d sublattices.     

Magnetite thin films

A low temperature process for converting hematite (α-Fe2O3) thin films into magnetite (Fe3O4is described. The films produced are unambiguously identified as magnetite by several complementary methods of analysis. These include α-backscattering spectrography, X-ray powder diffractometry, and observations of electrical, magnetic, and optical properties.