Showing papers on "Ferrimagnetism published in 1969"

Determination of Magnetic Anisotropy and Porosity from the Approach to Saturation of Polycrystalline Ferrites

Abstract: From measurements of magnetization in the approach to saturation region of the hysteresis loop, a semiempirical method has been developed for determining reasonably accurate values of | K1 |/Ms and peff, the fraction of nonmagnetic volume of polycrystalline ferrimagnetic materials. The technique involves the precise measurement of magnetization at five values of applied magnetic field, and the subsequent solution of four linear simultaneous equations. In combination with a measurement of the ferrimagnetic resonance linewidth, it is also shown how the intrinsic single‐crystal linewidth may be estimated. The results for a variety of garnet and ferrite compositions are reported, and selected aspects of their behavior are discussed in terms of magnetic anisotropy, porosity, and linewidth. In particular, materials containing manganese appear to have large intensic linewidths, and it is considered to be highly probable that octahedral‐site Mn3+ ions with short spin‐lattice relaxation times are responsible for t...

Ferromagnetic to Canted‐Ferrimagnetic Transition in Fe(Pd, Pt)3

Abstract: Magnetization and neutron‐diffraction measurements were made on the pseudo‐binary Cu3Au‐type ordered alloys Fe(PdxPt1−x)3 down to 4.2°K. The magnetic transition reported earlier for compositions near x=0.6 is found to correspond to a rapid but continuous change, as the temperature is lowered below ∼140°K, from pure ferromagnetism (as in FePd3) to a state in which the Fe moments open out into a simple canted structure (with two sublattices arranged identically to those in the pure antiferromagnet FePt3). The Pd, Pt moments are always parallel to the net ferromagnetic Fe moment; these moments vanish for compositions x<0.5. The occurrence and nature of this transition can be readily explained within a molecular field model in which the Pd, Pt moments are induced by and are a rapidly saturating function of the net exchange field from the Fe moments.

Ferrimagnetic garnet thin films: Growth, structure and some magnetic properties

Abstract: Ferrimagnetic garnet films, mainly gadolinium iron garnet, were deposited on fused-quartz substrates and subsequently heat-treated. They were studied by optical microscopy, X-ray analysis, and electron microscopy. Magnetic properties were measured and domains observed by employing the Faraday magneto-optic effect. Structure and properties were found to depend on growth parameters established in the heat-treatment step. The role of chemical factors in promoting the observed anomalies in structure (such as precipitation of Gd2O3 particles) and in properties (like the unusually high compensation temperature of the thinner films) is emphasised in the discussion of results.

Coupling between ferrimagnetic insulators through a superconducting layer.

Abstract: In agreement with a recent theoretical prediction of de Gennes, the transition temperature of In (or another superconductor) films sandwiched between two magnetic films depends on the relative orientation of the magnetization of these ferrites. The highest transition temperature (nearly the ${T}_{c}$ of bulk In, 3.4\ifmmode^\circ\else\textdegree\fi{}K) is obtained when the two ferrites are deposited in antiparallel magnetic fields, while the lowest (\ensuremath{\simeq}1\ifmmode^\circ\else\textdegree\fi{}K) occurs when the ferrites are deposited in parallel magnetic fields. The depression of the transition temperature of an indium film sputtered or evaporated between two magnetic films magnetized in parallel fields is inversely proportional to the thickness of the In film.

First‐Order Magnetic Transitions in (Fe, Mn)≥2As

Abstract: First‐order Fi→AF transitions, with increasing temperature, have been observed in the system Fea−xMnxAs when a=2.00 to 2.35. The transition temperature, Ts, is strongly dependent on the Mn/Fe ratio and can be set over the range <273° to 345°K. Similar transitions, recently reported for Fe1.95−xMnxAs, are limited to Ts<153°K. The transition, which involves no change in the P4/nmm crystal symmetry, is accompanied by a discontinuous decrease in crystal volume with increasing temperature. Saturation magnetization, σ, ΔV/V, and field coefficients, dH/dT, were measured. Typical properties when Ts=286°K are: σ=14 emu/g, ΔV/V=0.58%, dH/dT=3680 Oe/deg, dP/dT (calc)=60 atm/deg, ΔS (calc)=0.23 cal/mole deg. Measurements of σ vs H, parallel and perpendicular to c, the tetragonal axis, show the basal plane to be the preferred direction of magnetization with anisotropy fields near 36 000 Oe. The magnitude of σ, and its unusual temperature dependence, indicate ferrimagnetic ordering in the low‐temperature state.

Optical Studies of Ho3+ Ions in YGaG and YIG

Abstract: Optical absorption and emission spectra are used to determine the energy levels of the 5I8 ground state and 5I7 excited state of Ho3+ in diamagnetic yttrium gallium garnet (YGaG) and ferrimagnetic yttrium iron garnet (YIG). The results for YGaG are consistent with the D2 site symmetry of the dodecahedral site in the garnet structure. Energy levels in YIG that are separated by site inequivalency are identified from spectra observed as the Fe3+ magnetization is rotated in the (110) plane. Stimulated emission is observed from Ho3+ in YGaG at 2.086 and 2.114 μ and from Ho3+ in YIG at 2.086, 2.089, and 2.107 μ. Each of the lines in YIG is composed of two superimposed electronic transitions. The exchange field in YIG makes possible magnetic tuning of coherent emission over a range of 70 A. This paper is a brief description of work that will be treated in full elsewhere.

Magnetic form factor of thulium metal.

Abstract: The magnetic form factor of thulium at 4.2°K has been measured with polarized neutrons. The low‐temperature magnetic structure of thulium1 is the 4+, 3− ferrimagnetic configuration, in which the spins are aligned along the c axis. The net ferromagnetic component is 1μβ per atom. With the exception of the two innermost reflections the experimental observations are in excellent agreement with the 4f12 form factor. The anisotropy in the magnetization density has been confirmed by using an elevated counter technique. For the low‐angle reflections an additional contribution to the form factor is present. We have attributed this contribution to a 5d‐like conduction polarization. A calculation using free‐atom wave functions gives a 5d form factor that is in reasonable agreement. However, the magnitude of the 5d‐like contribution is six times greater than that generally regarded as the conduction electron polarization in thulium. This discrepancy could be explained if some modification of the 4f wave functions oc...

Distant-Neighbor B-B Interactions in Cobalt Chromite

Abstract: We have recently shown that five distinct distant‐neighbor B‐B exchange interactions can play significant roles in determining the ground‐state spin configuration in chromium spinels having nonmagnetic A‐site ions. This investigation is now extended to materials with magnetic A‐site ions and is further generalized to include A‐A interactions. The results are used to reinterpret our experimental findings for cobalt chromite. Reasonable values for the distant‐neighbor interactions lead to an eight percent decrease in the theoretical wavelength of the minimum‐energy ferrimagnetic spiral, which brings it into agreement with the observed value. Furthermore, inclusion of these values in the minimization of the free energy (in the molecular‐field approximation) leads to the prediction of an additional magnetic transition (where a phase angle vanishes) at about one third of Tc. The resulting kink in the computed variation of magnetization with temperature is in close agreement with experiment. Our neutron‐diffrac...

Resonance in Magnetically Ordered Crystals with Anisotropic g Factors

Abstract: The equations of motion of the sublattice moments are discussed in the case of anisotropic g factors when the lengths of mechanical moments are conserved, or are not conserved. Experimental data on magnetic resonance in hexagonal ferrimagnet RbNiF3 and orthorhombic canted antiferromagnet NaNiF3 are interpreted on the basis of such equations with the suggestion that the lengths of mechanical moments are conserved. It is shown that for both crystals the g‐factor anisotropy must be taken into account.

Ferromagnetic Resonance in Single‐Crystal BaO·6Fe2O3

Abstract: The theory of magnetic resonance in a highly anisotropic, uniaxial ferrimagnet is summarized and curves for the resonance behavior of BaO·6Fe2O3 as a function of applied field, parametrized with respect to angular orientation, are presented. Microwave ferrimagnetic resonance experiments performed from 66 to 120 GHz in a broad‐band, low‐Q waveguide system with applied magnetic fields up to 60 kG are reported. Sample temperatures ranged from 4.2° to 300°K. Good agreement between theory and experiment is found for spherical, single‐crystal samples. Samples of platelet geometry were also investigated. A brief discussion of observed magnetostatic modes is presented, along with evidence of nonlinear resonance response in BaO·Fe2O3 at 4.2°K for rf powers above 60 mW in the waveguide. The observed resonance linewidth was less than 10 G at 4.2°K.

Ultraviolet Magneto‐Optical Properties of Single‐Crystal Ferrimagnetic Ferric Oxide Compounds

Abstract: The first uv measurements of the complex polar‐Kerr effect (rotation and ellipticity) are reported between 1.7 and 5.64 eV for representative ferrimagnetic ferric oxide compounds containing both octahedral (Feoct) and tetrahedral (Fetet) sites. Room‐temperature measurements on bulk single crystals of pure and Ga‐doped rare earth iron garnets, spinel ferrites, and magnetoplumbite are used to distinguish between the contributions of Feoct and Fetet to the magneto‐optical spectra. Analysis shows that charge‐transfer transitions at about 4 and 5 eV, associated with Feoct and Fetet, respectively, are responsible for the principal uv magneto‐optical spectra of all the compounds studied. A model based on anisotropic orbital quenching explains why magneto‐optical effects in the orthoferrites are of the same order of magnitude as those in the ferrimagnetic ferric oxide compounds, even though the net magnetizations of the latter are typically an order of magnitude larger.

Erratum: Approximate Solution for the Strain‐Induced Deviation of the Magnetization from Saturation in Polycrystalline Cubic Ferrites

Abstract: The strain‐induced uniaxial magnetic anisotropy can cause a deviation in the magnetization from saturation along the applied magnetic field. An approximate variational solution is found for the necessary threshold strain or stress and for the amplitude of this deviation in thick, semi‐infinite slabs of cubic polycrystalline ferro‐ or ferrimagnetic materials. The resulting solutions are compared to solutions obtained from the linearized Brown's equations for equilibrium. Specific calculations are made for nickel ferrite, YIG, and magnetite.

THE LOW TEMPERATURE MAGNETIZATION OF Mn(CH3COO)2.4H2O.

Abstract: : Magnetization isotherms in fields up to 15 kOe have been measured at temperatures between 1.5 and 4.2K for monoclinic single crystals of manganous acetate tetrahydrate. Continuous, quasistatic isotherms were obtained with the field along three orthogonal axes, a, b, and c'. The magnitude of the saturation moment is consistent with a ferrimagnetic arrangement of Mn(++) moments (S = 5/2, g = 2) on two kinds of inequivalent lattice sites in the ratio of 2:1. The threshold effect suggests, however, that the system combines metamagnetic properties with those of ferrimagnetism. (Author)

Arc and spark extinguishing contacts utilizing single domain magnetic particles

Abstract: This invention relates to contacts which have about 0001 to 96 percent by weight of ferromagnetic or ferrimagnetic permanent magnetic particles embedded in the contacts such that the magnetic particles are distinguishable from the basic contact material The Curie temperature of the magnetic particles used in the contacts are greater than about 250* C and the magnetic particles have an average spontaneous magnetic energy product greater than about 5,000 GaussOersted The magnetic particles having spontaneous magnetic energy can also be incorporated in certain contact configurations to also obtain excellent noise suppression characteristics

Single crystal ferrimagnetic films

Abstract: A process for preparing single crystal ferrimagnetic films having square hysteresis loops, a regulated coercivity, and a compensation temperature above 250* K. A film of gadolinium iron garnet wherein a carefully selected amount of terbium or dysprosium replaces part of the gadolinium is deposited on a tytrium or rare earth aluminum garnet substrate having (111) or (100) orientation and heated until crystallization occurs.

Temperature-dependence of the cation distribution in ferrimagnetic spinels

Abstract: The cation distribution at some equilibrium temperature in ferrimagnetic spinels can be inferred provided the contributions to the cationic site energies are established. In some compounds, e.g. magnesioferrite, the distribution is strongly dependent on temperature. This is explained by taking into account suitable thermal energy terms in addition to electrostatic or crystal-field octahedral stabilisations. The Fe3O4/MgδFe3−δO4−(δ−1)/2 system is considered and the temperature-dependence in magnesioferrite is discussed. A comparison is made of the theoretical derivation with several experimental data.

Magnetoelastic wave propagation in single-crystal lithium ferrite

Abstract: The time delay of a magnetoelastic wave traveling in a constant field gradient is obtained for a lossless ferrimagnet without the use of the small-coupling approximation. The theory is used to calculate the delay of microwave pulses in lithium ferrite and in yttrium iron garnet single crystals. Echoes delayed by magnetoelastic wave propagation in a rectangular bar of single-crystal lithium ferrite are reported.

Transmission element for magneto-optical applications, particularly for the modulation of infrared radiation in the wavelength range between 1 and 20 microns

Abstract: A novel magneto-optical transmission element consisting of a substrate transparent to radiation in the wavelength range between 1 and 20 microns having thereon a monocrystalline or polycrystalline layer of a material having a spinel structure, a magnetic permeability, in vacuo, μ 0 = B/H exceeding 12 at temperatures lower than the Curie point, ie the material is either ferromagnetic or ferrimagnetic, a resistivity at the Curie point exceeding 100 ohm-cm and a chemical composition having the formula A Cr2 Z4, Z being selenium, sulfur, or telluorium and A being in general a divalent metal or complex, preferrably cadmium The transmission element may also serve as a memory element in which information therein can be read out by determining the sign of the remanent magnetization thereof by means of polarized infrared radiation

Magnetic tapes comprising ferrimagnetic materials

Abstract: MAGNETIC RECORDING TAPE COMPRISING A SUPPORTING MATERIAL AND A COATING COMPRISING A PLURALITY OF PARTICLES, EACH OF SAID PARTICLES COMPRISING A FERRIMAGNETIC MATERIAL SUBSTANTIALLY SURROUNDED BY AN ANTIFERROMAGNETIC MATERIAL, SAID FERRIMAGNETIC MATERIAL BEING MAGNETICALLY COUPLED TO SAID ANTIFERROMAGNETIC MATERIAL BY EXCHANGE ANISOTROPY, EACH OF SAID PARTICLES HAVING AN AVERAGE PARTICLE SIZE BELOW 1 MICRON, A PORE VOLUME ABOVE 0.02 CC. PER GRAM AND A SURFACE AREA ABOVE 2 SQUARE METERS PER GRAM.