bluuebunny/crossref_metadata_2025_split huggingface dataset:
Critical Magnetic Scattering from Dysprosium Aluminum Garnet (DAG)
Authors: Norvell J. C. , Wolf W. P. , Corliss L. M. , Hastings J. M. , Nathans R. 
Published: February 2004

We have measured the critical magnetic scattering and the temperature dependence of a Bragg magnetic peak in DAG from TN−T=0.14°K to T−TN=0.04°K. Specific heat and magnetic measurements indicate that DAG behaves like a three-dimensional Ising antiferromagnet with dipolar forces accounting for more than half the magnetic interaction energy.1 The neutron data have been compared with recent theoretical calculations for near-neighbor three-dimensional Ising models.2,3
The critical scattering was measured in the range 0&lt;q&lt;0.15 Å−1, 0.007&lt;ΔT/TN&lt;0.017 and was found to exhibit Lorentzian shape. The temperature dependence of the inverse range parameter κ was fitted by a weighted least-squares procedure to2logκa=νlog[(T−TN)/TN]+B0,giving (on a relative scale) TN=2.5179±0.0003°K and ν=0.60±0.02, which is lower than the Ising model prediction of ν=0.64. For B0∼0.33, as indicated by theoretical calculations, the correlation distance a was found to be ∼4.8 Å, consistent with the value 4.3 obtained from computation of the second moment of the experimentally determined interactions in DAG. The intensity of coherent magnetic scattering, I, was measured in the range 0.001&lt;ΔT/TN&lt;0.056 and was fitted by least squares to the expression I∼[(TN−T)/TN]2β[1−2b(TN−T)/TN].For b=0, we have found β=0.27±0.01 and TN=2.5179±0.0006°K, in agreement with TN obtained from the critical scattering. For b=0.83, suggested by Ising model calculations,4 the corresponding values are β=0.29±0.01 and TN=2.5182±0.0006, and the value of ν is decreased to 0.58, which is just within the estimated error. In either case the value of β falls significantly below the expected value of 0.312.
Mössbauer Effect in Yttrium- and in Samarium-Iron Garnets
Authors: VAN Loef J. J. 
Published: February 2004

Magnetic hyperfine fields and electric quadrupole splittings at the tetrahedral (D) and octahedral (A) iron sites in powdered samples of YIG and SmIG have been measured by means of the Mössbauer effect at various temperatures between 85° and 600°K.
From the room-temperature Mössbauer spectra it follows that in YIG the magnetization is along the [111] axis, whereas in SmIG the magnetization is in the [110] direction. In SmIG, a Curie temperature of 573.4±0.3°K has been found. From a comparison of the resultant moment of the iron sublattices with the total magnetization of SmIG as measured by Geller et al., a crossover near 300°K is apparent.
Magnetic Properties and Texture of an Ordered Pt–Co Single Crystal
Authors: Brissonneau Pierre , Blanchard André , Schlenker Michel , Laugier Jean 
Published: February 2004

A study of the magnetic properties of a completely ordered Pt–Co single crystal indicates that, out of the three possible sets of crystallites, one has a population twice as large as each of the two others.
This result can easily be interpreted in terms of a model of the distribution of the ordered crystallites leading to minimum strain energy. This model is presented and its experimental verification through x-ray and metallographic examination discussed.
New Low-Magnetostrictive Permanent-Magnet Alloys
Authors: Nesbitt E. A. , Chin G. Y. , Jaffe D. 
Published: February 2004

Some present day applications require magnetic materials to be used while being stressed in a complex manner. Of current interest would be a ductile material that has a square hysteresis loop, a magnetic saturation of approximately 18 000 G, a coercive force in the range of 10 to 20 Oe, and, in addition, a very low value of magnetostriction. It has recently been found that some of the face-centered cubic alloys of the Co–Fe–Au system fulfill these requirements. The level of coercive force is controlled by gold additions and by precipitation aging. Detailed study on an alloy of 82% Co, 12% Fe, and 6% Au showed that the coercive force is increased by increasing the degree of cold work prior to the aging treatment. Furthermore, the aging temperature for the peak value of coercive force varied greatly with the degree of prior cold work. For wire initially solution heat-treated at 1050°C, the coercive force peak occurred at an aging temperature of 775°C; whereas for wire initially cold-drawn 97.5%, the peak occurred at 550°C, a decrease of 225°C. Thus, the kinetics of precipitation is greatly facilitated by prior cold work in this alloy.
The 82% Co, 12% Fe, and 6% Au alloy exhibits a very low strain sensitivity, the coercive force changing only a few percent under a tensile stress of 5 kg/mm2. A squareness ratio better than 0.85 is obtained after appropriate treatment.
Truncated Green's Function Theory of the Kondo Effect
Authors: Hamann D. R. 
Published: February 2004

The interaction of a single magnetic impurity with metallic conduction electrons was recognized as a unique and difficult many-body problem when Kondo found that a perturbational treatment of this system diverged. One nonperturbative approach that has proved quite tractable for this problem is the truncated equation of motion method for double-time temperature-dependent Green's functions. The lowest-order truncation, corresponding to a generalized Hartree approximation, was first studied by Nagaoka. This same approximation is used to derive a single integral equation for the conduction electron t matrix.1 This equation is solved exactly,2 and the solution is compared with several previously found approximate solutions. It is also compared with the results of Suhl's scattering formulation, and found to be essentially identical. The properties of the system vary smoothly with temperature, and calculated results for the resistivity, spin susceptibility, and specific heat are discussed.
A full account of the author's contributions will be found in the references.
Magnetoelastic Effects
Authors: Auld B. A. 
Published: February 2004

The purpose of this paper is to review the present status of magnetoelastic effects in ferrimagnets. One of the most important fundamental developments in magnetoelastics has been the establishment of a correct continuum formalism for magnetoelastic coupling. This includes the volume couple exerted on the elastic system by the magnetization, and also makes use of finite strains in obtaining the energy density. Much remains to be done in evaluating the experimental and practical consequences of this work, but its validity has already been verified in measurements on the morphic and intrinsic effects in yttrium iron garnet. On the atomic level, magnetostrictive coupling has been related to pressure-induced shifts in optical spectra, and the constants for several materials have been measured by this method.
Both linear and nonlinear phenomenological effects are of current interest for device applications. Linear delay lines and pulse compression filters are now at the stage of engineering evaluation. Some novel processes in time-varying media have been shown experimentally to provide signal transformations such as frequency translation and frequency chirping of pulses. Although the experimental characteristics of magnetically pumped instabilities in delay lines have been examined in considerable detail, correlation with theory remains unsatisfactory. A new type of nonlinear process, the Hahn-type of echo, has been observed and analyzed in ferrimagnets. Phonon pumping of spin-wave and magnetoelastic-wave instabilities is being studied experimentally and theoretically.
Theory and Experiment in Magnetic Recording
Authors: Speliotis D. E. 
Published: February 2004

The traditional dominance of gamma ferric oxide as the ferromagnetic constituent of recording media is currently being challenged by the development of new particles, such as chrome dioxide and metallic particles, as well as thin metallic films of high coercivities. These new materials allow for a large variation of the magnetic properties and the thickness of the recording surfaces, and offer considerably greater potential for recording optimization in high-storage applications. They have also brought about a renewed interest in the theory of magnetic recording, particularly pertaining to the correlation between the magnetic properties and recording performance.
In this paper we discuss the present status of theory and experiment in magnetic recording. It is concluded that our present theoretical understanding is such as to adequately explain the geometrical aspects of the recording process—transducer to medium spacing, transducer gap length, and medium thickness—but less than adequate in characterizing the magnetic state of the recording media.
Magnetic Properties of Antiferromagnetic GdAlO3
Authors: Cashion J. D. , Cooke A. H. , Hawkes J. F. B. , Leask M. J. M. , Thorp T. L. , Wells M. R. 
Published: February 2004

Specific-heat and magnetic-susceptibility measurements on GdAlO3 show that it undergoes a transition to antiferromagnetism at 3.69°K. Magnetization measurements on a single crystal at temperatures down to 0.6°K in fields up to 70 kOe show that the ordered state is a simple two-sublattice structure with the orthorhombic b axis as the axis of alignment. The spin flop, exchange, and anisotropy fields have been found to be 11.2 kOe, 20 kOe to 25 kOe, and 2.3 kOe to 3.0 kOe, respectively. No parasitic ferromagnetism is observed.
Optical absorption studies of Er3+ and Dy3+ in GdAlO3 observe the spin flop and confirm that in the ordered structure the distorted simple cubic lattice of Gd3+ ions divides into two sublattices with each ion surrounded by six nearest neighbors belonging to the opposite sublattice.
Very Thin (2–200 Å) Ferromagnetic NiFe Films
Authors: Gradmann Ulrich , Müller Joachim 
Published: February 2004

The magnetization of flat, single-crystal NiFe (111) films (45% to 50% Ni) was measured for 70∘≦T≦400∘K. There is good qualitative agreement with spin-wave theory for the dependence of the magnetization on temperature, at least for films consisting of 3 to 20 layers. Yet there are two characteristic deviations from theoretical expectations:
(1) Down to 3 layers (6 Å) the magnetization is independent of the field, within 1%, for 300≦H≦5000 Oe, while theory predicts considerable dependence on the field.
(2) Above 30 layers, the film magnetization at low temperatures is definitely less temperature dependent than the bulk magnetization.
The deviations are supposedly connected with strong anisotropies, with the surface normal as easy axis, which are nearly proportional to the reciprocal of the film thickness and may therefore be interpreted as surface anisotropy (about 0.23 erg/cm2 at 250°K).
Critical temperatures are given for films consisting of up to 6 layers.
Status of Experiments on Far-Infrared Absorption Spectroscopy in Magnetic Material
Authors: Wheeler R. G. , Reames F. M. , Wachtel E. J. 
Published: February 2004

Current experimental techniques in far-infrared spectroscopy applicable to the study of magnetic materials are surveyed. A comparison between interferometric and diffraction methods of wavelength isolation illustrates the use of weak incoherent radiation sources. Observation of electric and magnetic dipole transitions between the Stark levels of the ground state manifold in rare earth ethyl-sulfates demonstrates the indispensable value of magnetic field and radiation polarization techniques.
Experiments on antiferromagnetic resonance modes can provide information concerning the type of antiferromagnetic ordering as well as numerical values of exchange and anisotropy constants. Absorption spectra attributed to the creation of k=0 magnons via magnetic dipole transitions and to the creation of zone-edge magnons via two-magnon electric dipole transitions have been observed in 3d ion compounds. Recent results on the 5d ion compound K2IrCl6 allow some interesting comparisons.
Origin and Uses of the Faraday Rotation in Magnetic Crystals
Authors: Dillon J. F. 
Published: February 2004

Light transmitted by a magnetic crystal interacts with the magnetization. In particular, the axis of linear polarization undergoes a rotation proportional to the fractional projection of M on the direction of propagation. This magneto-optical rotation, the Faraday rotation in magnetic materials, has been studied for many years. The advent of insulating magnetic materials has led to renewed interest of two sorts:
(1) The rotational dispersion coupled with that of the absorption coefficient in some cases makes possible the spectroscopic assignment of optical transitions which show magnetic effects. Thus we may use the rotation to extract information on the magnetic behavior of energy levels well above the ground state.
(2) Any experimental or technological use of the rotation makes it necessary to take into account the attendant absorption of light. Some insulating magnetic materials have very high values of the rotation per unit attenuation. The magneto-optical rotation may then be used to ``see'' both dc (domain structure) and rf (magnetostatic spin waves) magnetization distributions within the crystal. Furthermore, the low rotation attenuation is crucial in a number of magneto-optical devices: rotators, wide-band modulators, phase shifters, memories, the YIG laser, etc.
Magnetic-Interaction Effects in Fine-Particle Assemblies and in Thin Films
Authors: Kneller E. 
Published: February 2004

In describing interaction effects, both the mean field and cooperative phenomena are pertinent. It is shown for different groups of materials how the interaction behavior is derived from the characteristic structural features of a material by suitably combining mean field and cooperative effects.
With respect to interaction behavior there are two main types of materials: type I where the anhysteretic susceptibility χα is finite, and type II where χα=∞. As for single-domain particles, suspensions are type I when the dynamic mean interaction field satisfies a certain condition; otherwise they are type II; precipitation alloys are either type I or type II depending on a criterion for particle axes alignment with respect to field direction, or on coercivity. Assemblies of multidomain particles are always type I. Uniaxial 19Fe81Ni evaporated films behave analogously as suspensions.
The effects of interactions on χα and on remanence curves of these materials are treated in some detail, also with regard to the effects of packing fraction p and field orientation.
Electron-Magnon Scattering and Polarization of the Scattered Beam
Authors: DeWames R. E. , Vredevoe L. A. 
Published: February 2004

The use of electron-magnon scattering as a probe of the magnon spectrum and as a means for producing polarized electron beams is discussed. Recently Boersch et al.1 have demonstrated the feasibility of measuring small energy losses (∼0.006 eV) for electrons of energies up to 60 keV. Consequently, the contribution of low-energy inelastic processes, such as electron-phonon1 and electron-magnon scattering, to the scattered beam is now experimentally accessible. Unlike neutron-magnon scattering, where the only contribution to the interaction Hamiltonian come from the dipole-dipole interaction, the most important mechanism for electron-magnon scattering at moderate energies arises from the exchange interaction.
Starting from the basic Hartree-Fock equations we obtain expressions for the differential scattering cross sections for a general magnetic system. For high-energy electrons it is shown that the effective exchange interaction is energy dependent and varies inversely with the incident electron energy. In contrast to the electron-phonon differential scattering cross section, the electron-magnon differential cross section is peaked in the forward direction. For a ferro- or ferri-magnetic system it is shown that highly polarized (∼100% for the ferromagnetic case) electron currents can be obtained having intensities comparable to those of other techniques.
Diffuse Elastic Neutron Cross Section for an Impurity in a Heisenberg Antiferromagnet
Authors: Lovesey S. W. 
Published: February 2004

Spin-wave theory of a Heisenberg antiferromagnet predicts a zero-point spin deviation η from the assumed ground state, namely, the Néel state. Measurements of η using NMR in a number of compounds give values substantially smaller than that given by spin-wave theory.
The object of this paper is to present the theory necessary to allow the measurement of η by magnetic scattering of thermal neutrons from an antiferromagnet containing a weak concentration c of nonmagnetic impurities. The diffuse elastic cross section for such a system is dσ/dΩ=(γe2/2mc2)2(1−̂z2)Nc(1−c)F2(κ) 〈Sz〉2 | Q(κ−τ) | 2,where 〈Sz〉 is the thermal average of the unperturbed host spins, Q(κ) the Fourier transform of the deviations in the z components of spin from 〈Sz〉 due to an impurity and all other symbols have their usual meaning. It is evident that η may be measured provided Q(κ) is known. We have calculated Q(0) for a body centered antiferromagnet of arbitrary spin in the linear spin-wave approximation. This has been achieved using thermal Green functions which also permits the dynamics of the system to be investigated.
The Effect of Plastic Deformation on the Magnetic Aftereffect in Iron
Authors: Rusnak R. M. , Cullity B. D. 
Published: February 2004

The interstitial diffusion-controlled magnetic aftereffect in polycrystalline iron was measured at 23°C and at a constant applied field in the Rayleigh region as a function of the amount of plastic prestrain in the sample (from 0.04% to 3.8% tensile strain). The magnitude of the aftereffect was found to vary with the strain ε according to the following relationship 1/Ba0 = k0+k1ε1/2, where Ba0 is the magnitude of the aftereffect (total aftereffect induction) and k0 and k1 are constants.
The aftereffect magnitude Ba0 was found to be proportional to dB/dH for all the prestrain values of this investigation and therefore the decrease of Ba0 with strain was attributed entirely to increased, stabilization-independent, resistance to domain wall motion while the stabilization force remained constant with strain. The proportionality constant may be considered as a fictitious magnetic field Hf(Ba0 = HfdB/dH) with a value of 0.02 Oe for an iron sample which contains 23 ppm carbon and 20 ppm nitrogen.
The aftereffect kinetics were found to be independent of prestrain, as reflected by the constancy of the ratio of the aftereffect induction of the nondeformed sample to the aftereffect induction of the prestrained samples over the time interval of the aftereffect.
Magnetostrictive Crystalline Energy of Dislocations in Ni Single Crystals and the Anisotropy of the Approach to Saturation
Authors: Gessinger H. , Köster E. , Kronmüller H. 
Published: February 2004

Recent micromagnetic calculations have shown that magnetostrictive interactions of internal stresses with the magnetization produce an additional magnetocrystalline energy. In cubic crystals the additional anisotropy energy processes orthorhombic symmetry.
The crystalline energy induced by plastic deformation in Ni single crystals (oriented for single glide) has been investigated through an analysis of the anisotropy of the approach to saturation. Measurements were carried out on cylindrical disks for different applied fields and several degress of deformation. In particular in the (111)-plane the plastically deformed disks show a twofold and a fourfold symmetry axis in addition to the sixfold symmetry axis of the ideal crystal.
Thermally Activated Dislocation Depinning in Dilute Copper Alloys
Authors: Saul Robert H. , Bauer Charles L. 
Published: February 2004

Internal friction and Young's modulus measurements have been performed on a series of dilute copper—silicon, copper—germanium, and copper—tin alloys at temperatures ranging from 4° to 300°K in order to determine the extent of thermally activated dislocation depinning from solute atoms. Specimens are in the form of singel-crystal bars, and are excited piezoelectrically in their fundamental longitudinal mode of vibration at 80 kHz.
For temperatures in excess of 180°K, the amplitude-dependent internal friction is characterized by an Arrhenius temperature dependence with an activation energy that varies linearly with the stress amplitude. A low-temperature modification of the Granato—Lücke theory accounts for the temperature dependence of the internal friction below about 120°K; however, the stress dependence is contradictory to that predicted theoretically. In general, thermal depinning is enhanced at high temperatures and stress levels, and in crystals containing long dislocation segment lengths and solute atoms of low pinning strength.
Magnetic Properties of an Equi-Atomic PtCo Single Crystal Having a [111] Orientation
Authors: Walmer M. S. 
Published: February 2004

The equi-atomic alloy of PtCo (77 wt% Pt, 23 wt% Co) is a high energy product, high coercive force permanent magnet material. Polycrystalline magnets of PtCo are isotropic. Measurements of the intrinsic coercive force as a function of crystallographic orientation made on a small PtCo single crystal showed it to be anisotropic. The maximum Hci value was found to occur in the 〈111〉 direction. Subsequently, a larger single crystal was produced in the form of a right circular cylinder for the purpose of making B-H measurements in the [111] direction. Values were obtained for Br, Hc, Hci, and (BH)max from hysteresis graphs of both the single-crystal PtCo magnet with a [111] orientation and the conventional isotropic polycrystalline PtCo magnet.
Values measured were: BrHcHci (BH)maxSingle crystal 〈111〉6500590082009.8×106Polycrystalline6400550075009.2×106.
Magnetization Studies in Nb 3Sn and Ti–Nb Alloys
Authors: McInturff A. D. , Paskin Arthur 
Published: February 2004

Magnetization measurements were performed on commercial Nb3Sn and Ti–Nb alloy samples to determine hysteretic loss (magnetization vs magnetic field) and flux-jump stability at 4.2°K in magnetic fields up to 9.3 Wb/m2. The aforementioned superconducting properties were also observed and recorded with various geometries, field sweep rates and thermal environments. The samples consisted of ribbons and/or wires ranging in size from 1.0 to 0.1 cm wide and 0.1 to 0.0001 cm thick. The transport currents ranged from a few amperes to greater than a thousand amperes. These data were obtained utilizing an experimental setup similar to that described by Fietz. The shape and magnitude of the magnetization curves with and without the presence of transport current was not a function of frequency in the range employed, 0.012 to 3.0 Wb/m2·min, except for the multifilament composites. The magnetization and flux-jump stability was found to be a function of the sample dimensions, as would be expected with the earlier expressions given by Wipf, Hancox, Chester, and Stekly. The transport current density was not a function of the dimensions. These data on magnetization and transport current effects are in accord with earlier work by LeBlanc and co-workers on Nb–Zr. There is a first principle derivation of the flux-pinning effects that uses a Josephson junction tunneling model and results in the Kim-Anderson expression. The internal field distribution could be characterized by Hint(x)=(Ha−Hs exp(−x/λ)+Hs,  λ=(Hs−Ha)/Jc(Ha).
The exponential expression for Jc(Ha) vs Ha of Fietz et al. fits the sample data; however, the Kim-Anderson expression that would be the first term in the expansion of the exponential would also fit the observed data within the experimental error. The data concerning transport current and magnetization can be accurately accounted for (in the infinite sheet configuration) by expressions derived by Yasukochi. The thin plate geometry, with the proper demagnetization factor, is in agreement as well.