bluuebunny/crossref_metadata_2025 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<q<0.15 Å−1, 0.007<ΔT/TN<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<ΔT/TN<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.
Magnetic Scattering of Neutrons in MnF2 near the Critical Point
Authors: Parette G. , Deniz K. Usha
Published: February 2004

The angular distribution of slow neutrons (λ=4.34 Å) scattered from a single crystal of MnF2 has been studied as a function of temperature in the vicinity of the Néel point, about the (100) and the (001) reciprocal lattice points. The (001) data have been analyzed to obtain the values of χs⊥, the transverse staggered susceptibility, and its variation with temperature above the transition point has been examined in the light of the theories of Moriya and Tomita. Moriya's theory shows that χs⊥ is proportional to (T−T⊥)−1 where (TN−T⊥) is calculated by him to be 1.36°K. To give a good fit to our values, an expression of the type (T−T⊥)−γ has been used for χs⊥ with Moriya's value for (TN−T⊥), and γ is found to be 0.85. A much better fit is obtained by using the expression for χs⊥ suggested by Tomita, namely, C{A + B(T − TN)γ}−1, for A=0.016 and γ=1.22. The longitudinal staggered susceptibility, χs∥, has been deduced from the measurements around the (100) point. Its temperature dependence above TN is found to be of the form (T−TN)−1, and is not consistent with a four-thirds power law.
Magnetization of Nickel near its Critical Temperature
Authors: Noakes J. E. , Arrott A.
Published: February 2004

Magnetic properties of a single-crystal sphere of nickel as a function of temperature and applied field have been measured in the critical region. The dependent variable, directly measured, is proportional to MV/B where B is the applied field and MV is the magnetic moment of the sphere in the direction of B. Below TC and for B <4πMs(T) /3, where Ms(T) is the spontaneous magnetization, M/B=3/4π. This serves as an absolute calibration of the measurement. Three types of data have been taken: (1) M/B at constant T for 20 G<B<1000 G in 2-G steps for steps of ΔT/TC=3×10−4 from TC−0.01 TC to TC+0.01 TC; (2) M/B at constant B in steps of ΔT/TC=3×10−6 from TC−0.01 TC to TC+0.01 TC for B=20, 240, 500, and 5000 G; (3) B at constant M/B in various steps of ΔT/TC for various values of M/B near 3/4π and near 0.2. From a partial analysis of the data we find an approximate equation of state for Ni. It is: (H/M)0.764=(T−TC)/0.309+ |M/39.5| 2.59. This equation of state fits well to the data of Weiss and Forrer also. But it does not fit for small values of H/M. The initial susceptibility fits better to (H/M)0.764=(T−TC)/0.345.
Satellite Lines in the 59Co Resonance in Cobalt-Nickel Alloys
Authors: Riedi P. C. , Scurlock R. G.
Published: February 2004

The distribution of effective field at the 59Co nucleus in alloys of composition CocNi1−c has been studied for c[similar or greater-than]0.93 using an automatic swept frequency spin-echo NMR spectrometer at 4.2°K. Three satellite lines were observed displaced approximately 7.5 MHz, 15 MHz, and 22 MHz below the main line at 217.4 MHz. The intensities of the satellite lines relative to the main line are in good agreement with the probabilities of configurations with one, two, and three nickela toms respectively in the near-neighbor shell. A further partially resolved satellite 2 MHz below the main line was also observed and attributed to nuclei with one nickel atom in the next-nearest neighbor shell and none in the first-neighbor shell. From these measurements it is concluded that the magnetic disturbance produced by a nickel atom in the cobalt lattice is well localized, in agreement with the neutron-diffraction measurements.
Electrical Resistivity of Some Dilute Gold-Rare Earth Alloys
Authors: Edwards L. Roger , Legvold Sam
Published: February 2004

The electrical resistivity has been measured from 1.3° to 20°K on solid solutions of Ce, Nd, Gd, Tb, and Ho in Au. It was found that the resistivity decreased monotonically with decreasing temperature with no evidence of a resistance minimum. However, for the Gd, Tb, and Ho in Au alloys, the resistivity showed a pronounced decrease in the temperature range 3.5° to 6°K. These results are discussed in terms of the Kondo theory. It was also found that the residual resistivity (4.2°K) is proportional to the concentration of rare earths for the Gd, Tb, and Ho alloys. Furthermore, the proportionality constant is the same for the three sets of alloys, indicating ionic (trivalent) scattering as the main contribution to the residual resistivity.
Core Polarization in 4dn and 5dn Configurations from ESR Data
Authors: Low W.
Published: February 2004

There are enough data from ESR spectra to permit evaluation of the core polarization within certain approximation. In the 4dn configuration this yields about 240 kG per unpaired spin. For the 5dn configuration the data are not as extensive. Preliminary estimates show that the value is about twice that of the 4dn.
Temperature Dependence of the Magnetic Moment and Effective Hyperfine Field of Sm3+ in SmIG
Authors: Nowik I. , Ofer S.
Published: February 2004

The experimental temperature dependences of the magnetic hyperfine field [Heff(T)] and the ionic magnetic moment [Ms(T)] of Sm3+ in SmIG are compared with theoretical predictions. A Hamiltonian, which includes spin orbit energy splittings, the exchange interaction, and a fourth-order cubic crystallinefield potential, was diagonalized within the 14 levels of H5/2+H7/2. Heff(T) and Ms(T) were calculated for various values of the exchange field Hexch at 0°K and the crystalline-field constant (B4). Fairly good agreement with experimental temperature dependences of both Ms and Heff is obtained with B4 = 485 cm−1 and β0 Hexch (0°K)/k=32°K.
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.
A Domain-Boundary Model for a High Coercive Force Material
Authors: Becker J. J.
Published: February 2004

The coercive force of aligned Co5 (rare earth) powders, while always much less than 2K/M, varies greatly with magnetizing field, even up to 50 kOe. The remanence is much more nearly constant. The coherent rotation model for noninteracting particles is not adequate to describe this behavior. A model is presented based on the idea that domain boundaries may be present and move easily, but that a sufficiently large field will drive them out so that they must be renucleated. Two experimental findings support this model. First, the measured rotational hysteresis integral value depends on whether or not a large field is applied before each measurement, as the model predicts. Second, magnetization jumps corresponding to nucleation have been directly observed in single particles. Calculations of the behavior of aggregates based on this single-particle model show the type of variation of coercive force and remanence that has been observed.
Band Theory and Metallic Antiferromagnetism
Authors: Yamashita Jiro , Asano Seturo , Wakoh Shinya
Published: February 2004

In 1951 Slater proposed that there is an intimate relation between the band structure and metallic antiferromagnetism. In this paper, we attempt to examine this relation by evaluating the band structure of perfect antiferromagnetic Cr and γ Mn by the Green's function method, and that of an ordered NiMn in the antiferromagnetic state by the tightbinding approximation. It is found that each of these substances has a very characteristic band structure, which seems to be quite favorable for antiferromagnetism.
Giant Spontaneous Hall Effect in 3d Ferromagnets
Authors: Fivaz R. C.
Published: February 2004

The large spontaneous Hall effect which is observed at low temperatures in ferromagnetic Fe and Ni may arise from accidentally degenerate states on the Fermi surface which are mixed by the spin-orbit interaction. The location of the Fermi level deduced from this interpretation agrees with the present knowledge of the Fermi surface in Ni but is not compatible with recent band calculations in Fe.
Anisotropy of the Magnetic Form Factor in 3d Ferromagnetic Metals
Authors: Hodges L. , Ehrenreich H.
Published: February 2004

A band theoretic explanation of the isotropy of the magnetic form factor of Co and its contrasting behavior with respect to Ni is shown to result both from the lowered Fermi level within the d bands and the more complicated form of these bands in hcp Co. APW calculations were performed for this purpose and used to construct an interpolated band picture for ferromagnetic Co assuming rigid d-band splitting. Some minor modifications of the Ni band structure proposed by us earlier are also discussed.
Orbital Susceptibilities of Transition Metals
Authors: Place C. M. , Rhodes P.
Published: February 2004

The information on the magnitude of the orbital contribution χorb to the magnetic susceptibilities of the transition metals which may be deduced from experimental data is briefly reviewed. Results of a calculation of χorb as a function of Fermi energy are given for electrons in (i) an fcc d band based on the tight-binding calculation of Fletcher and (ii) an interpolated bcc d band obtained from Wood's APW calculation for iron.
Some Properties of Iron deduced from a Tight-Binding Calculation
Authors: Asdente M. , Delitala M.
Published: February 2004

The first constant K1 of the magnetocrystalline energy of Fe has been evaluated by introducing the spin-orbit coupling as a perturbation as compared with the effects of the crystal field and the exchange energy. The latter has been treated as an additional energy ±δ to the various levels depending on the direction of the electron spin. Previous results obtained with the tight-binding approximation are used. A histogram of K1 as a function of the energy of the levels has been constructed which shows that the levels in the lower half of the band give a negligible contribution compared to that due to the ones in the upper half. Using 284 nonequivalent points of Brillouin zone, K1 is found to be positive, in agreement with the experimental data on the directions of easy magnetization, but its value is lower than expected. The 3d electron charge distributions for the t2g and eg symmetries are given as a function of energy. They show two peaks with a minimum in the middle of the band and the eg character predominates at the top and at the bottom of the band. Both the charge and spin densities show the same kind of deviation from spherical symmetry as the ones deduced respectively by x-ray and neutron-diffraction experimental results.
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.
Antiferromagnetism of γ-FeMn Alloys
Authors: Ishikawa Y. , Endoh Y.
Published: February 2004

The antiferromagnetism of disordered γ-FeMn alloys has been investigated mainly by neutron diffraction and Mössbauer effect for specimens with different compositions. The average atomic magnetic moment at 0°K decreases, but the Néel temperature increases with increasing Mn concentration. The hyperfine field at 0°K acting on the Fe nucleus, however, remains almost constant. The temperature dependence of the average magnetic moment is also different for different compositions. In contrast with it, the temperature dependence of the hyperfine field is independent of concentration and is markedly different from that of the average magnetic moment. The magnetic moments of iron and manganese have been separately determined by the magnetic diffuse scattering experiments at room temperature. The results indicate that both temperature and composition dependences of the magnetic moments of iron and manganese are quite different in γ-FeMn alloys.
NMR Study of Ferromagnetic Rare Earth Metals and Alloys
Authors: Itoh J. , Kobayashi S. , Sano N.
Published: February 2004

NMR of several rare earth elements were observed in ferromagnetic rare earth metals and alloys. Generally, the observed lines were split by a nuclear electric quadrupole interaction. By analyzing the observed changes of the magnetic and electric quadrupole hyperfine interactions of Tb and Dy in alloy systems of Tb–Dy, Tb–Gd, and Dy–Gd, as compared with those in pure metals, it is concluded that there exists a considerable contribution of conduction electron polarization to the magnetic hyperfine interaction and that of crystalline field to the quadrupole interaction. T1 and T2 of Dy in Dy metal were measured and it is suggested that Pincus-Winter mechanism and Suhl-Nakamura interaction contribute to T1 and T2, respectively.
Magnetic Anisotropies in Antiferromagnetic Rare Earth Antimonide Single Crystals
Authors: Busch G. , Vogt O.
Published: February 2004

The magnetic properties of the rare earth antimonides are anisotropic below ordering temperatures. In the compounds of Ce, Nd, Dy, and Ho the crystalline field confines the spin to the [100] axis. The observed uniaxial metamagnetism is explained in terms of the Ising model. The induced magnetic moments depend strongly on the direction of the applied field. This anisotropy is less pronounced in the cases of TbSb and ErSb, in good agreement with theoretical considerations. Metastable spin structures are observed in DySb, HoSb, and CeSb.
Anisotropy of Fe3+ Ions in Yttrium Iron Garnet
Authors: Pearson R. F. , Annis A. D.
Published: February 2004

Using the single-ion theory of anisotropy, it is possible to derive the anisotropy constants at 0°K for yttrium iron garnet in which the iron ions on tetrahedral and octahedral sites are replaced by nonmagnetic ions of gallium, indium, or scandium, respectively. The theoretical variation of K1 has been compared with experimental values derived from torque measurements on single crystals of Y3GaxFe5−xO12 (x=1.15), Y3InxFe3−xO12 (x=0.12, 0.20, 0.49), Y3ScxFe5−xO12 (x=0.87) between 1.5° and 300°K. Although the results of the tetrahedral substitution fit the sample theory, the results for octahedral substitution give values of K1 much lower than predicted. These values can be explained by assuming that the octahedral substitutions modify the crystal-field parameters of the unsubstituted Fe3+ ions and thus alter their contribution to the over-all magnetocrystalline anisotropy.
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.
Specific Heat of DyFeO3 from 1.2°–80°K
Authors: Berton A. , Sharon B.
Published: February 2004

Only one specific-heat anomaly was found in DyFeO3 in the range 1.2°–80°K, although two magnetic transitions have been reported in the literature. This λ-type anomaly at TN = 3.7°K is attributed to a magnetic ordering of the Dy3+ spin system. The magnetic and lattice contribution to the specific heat have been separated, finding θD = 390°±7°K.
Magnetic Behavior of Some Orthoferrites in the Anisotropy Change Region
Authors: Gyorgy E. M. , Remeika J. P. , Hagedorn F. B.
Published: February 2004

In a number of canted-spin rare earth (RE) orthoferrites, the easy axis for the spontaneous magnetization changes from the a to the c axis with increasing temperature. We have studied the magnetic behavior in the transition region using both torque and vibrating sample magnetometers with applied fields (Ha) from about 0.1 to 6.0 kG. The measurements were made with Ha in the ab, bc, and ac planes. The use of small values of Ha makes it possible to separate the effects of the weak ferromagnetism from the paramagnetism of the RE lattice. In Sm orthoferrite the reorientation occurs over about 20°, centered at 175°C (Tr). For this material in the ac plane the iron lattice is well described by the energy expression E = +½Ku cos2θ+kb cos4θ. Substantially below Tr, Ku≫Kb and the magnetization has a strong uniaxially preferred axis along a. As the temperature increases, Ku decreases and the easy axis splits symmetrically in two, one on each side of a, and these rotate toward c with increasing T. At 175°C, Ku∼0 and the torque curves have only a fourfold symmetry. For T increasing above Tr, Ku becomes increasingly negative, which leads to a uniaxially preferred axis along c. Analogous behavior has been observed for Tm orthoferrite. Here the reorientation occurs over about 12° centered at 86°K. However, for this material Kb is found to depend on the applied field. Furthermore the paramagnetic RE lattice has c as the easy axis for the whole temperature range. A result is the minimum total energy changes from Ha ∥ a to Ha ∥ c as Ha is increased for T < Tr.
Magnetic Properties of an Antiferromagnetic Orthoferrite
Authors: Gorodetsky G. , Sharon B. , Shtrikman S.
Published: February 2004

The orthoferrite DyFeO3, weakly ferromagnetic at room temperature, was found to become antiferromagnetic at 36°K. Symmetry considerations suggest that at this transition point the iron spin-axis rotates out of the plane perpendicular to the Moriya-Dzyaloshinsky vector, becoming parallel to it. On this basis the magnetic point group mmm is assigned to DyFeO3 below the transition. Further evidence for the correctness of this assignment has been obtained by the observation of a linear dependence of the susceptibility on the magnetic field χxy=CHz, and cyclic permutations as allowed by the mmm symmetry. Another transition, which we associate with an antiferromagnetic ordering of the Dy3+ moment, is found at TN=3.7°K. The magnetization curves measured below 4.2°K at fields up to 40 kG are interpretable, to a good approximation, in terms of |±15/2〉 Kramers' doublet whose axis lies in the mirror plane of the crystal, making an angle of approximately 30° with the [010] axis. Below TN metamagnetic transitions were observed. Symmetry arguments show that provided the chemical and magnetic unit cells are identical, the magneto-electric effect is allowed in DyFeO3 below TN.
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.
On the Direction of Magnetization in Ferromagnetic Thin Films
Authors: Corciovei A. , Vamanu D.
Published: February 2004

A microscopical description of the equilibrium direction of the spontaneous magnetization of thin ferromagnetic films is developed, taking into account in the Hamiltonian, besides the exchange term, also the dipolar and the magnetic anisotropy terms. The problem is studied with respect to the film thickness, magnetic anisotropy constant, and temperature. The first order of the Heisenberg's traces method for a free-energy minimization procedure was used. It is stated that the dipolar and anisotropy terms of the Hamiltonian fully determine the direction of the spontaneous magnetization.
Rare Earth Metal Single Crystals. I. High-Field Properties of Dy, Er, Ho, Tb, and Gd
Authors: Rhyne J. J. , Foner S. , McNiff E. J. , Doclo R.
Published: February 2004

Magnetic-moment measurements have been made along principal axes of Dy, Er, Ho, Tb, and Gd single crystals at 4.2°K and dc fields to 150 kOe. Dy and Tb showed similar magnetic properties. Saturation along the easy axis was achieved at low fields, while along the hard (c) axis the moment was nearly linear with field and did not approach saturation. Anisotropy was observed in the basal plane at low fields. An irreversible change in Dy and Tb occurred below 150 kOe for fields along the hard axis, such that subsequently saturation could not be achieved along the easy axis. Extrapolation of the low-field (unstrained) data along the hard axis indicated anisotropy energies of about 109 ergs/cm3. In Er significant modifications of the zero-field conical moment state were observed and theoretical saturation was almost achieved along the c axis. Fields applied in basal-plane directions collapsed the conical state and produced fan-moment distributions approaching saturation near 150 kOe.
Magnetic Properties of FeS2 and CoS2
Authors: Miyahara Syôhei , Teranishi Teruo
Published: February 2004

Magnetic properties of FeS2 and CoS2 having pyrites structure are studied. Magnetic susceptibility of a good natural pyrites (FeS2) crystal is almost temperature-independent down to 4.2°K. The constant susceptibility is explained by the Van Vleck paramagnetic term and diamagnetic one of the core. This suggests iron in pyrites is in divalent and low-spin state contrary to the assumption of L. R. Walker et al. that iron in pyrites is in a trivalent state from the Mössbauer isomer-shift data. CoS2 is a ferromagnet of a Curie temperature of 130°K. The spontaneous magnetization σ and the Curie constant Cmol are measured on a synthetic crystal of CoS2. We obtained the values, σ=44.4 emu/g and Cmol=0.37 emu·deg. The values are compatible when we assume Co is in divalent and low-spin state. This fact accords with the result of magnetic measurement of FeS2.
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.
The Invar Problem
Authors: Chikazumi S. , Mizoguchi T. , Yamaguchi N. , Beckwith P.
Published: February 2004

Anomalous thermal expansion and its relation to magnetic properties are surveyed for various Invar alloys. Saturation magnetization was measured for alloy systems (FexNi1−x)92M8, where M=Cu, Co, Mn, Cr, and V, and also for Fe70(RexPt1−x)30 at 4.2°K. Sharp drop of the saturation moment occurs at the average electron concentration, N=8.13 to 8.52, for all the Invar alloys including the above-mentioned alloy systems and N=8.21 to 8.52 for all the Fe–Ni base alloys. When, however, it was plotted against the electron concentration of the matrix surrounding less electropositive impurity atoms such as Mn, Cr, or V, all the alloy systems were found to exhibit a sharp drop of the moment in narrower concentration range of 8.48 to 8.60 for all the Fe–Ni base alloys. Saturation moment and a reversible susceptibility in the saturation range were also measured at room temperature for (110) [001] and (001) [110] rolled single crystals of the composition 29 at.% Ni–Fe. It was found that saturation moment was reduced from 79 to 72 emu/g, and the reversible susceptibility increased from 4.0 to 4.6×10−4 emu/g by 70% reduction of the thickness. The mechanism was discussed in relation to the well-known effect of cold rolling on the thermal expansion coefficient of Invar.
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.
Time Correlations and Magnetic-Resonance Linewidth in Finite Heisenberg Linear Chains
Authors: Carboni Fernando , Richards Peter M.
Published: February 2004

We have performed exact calculations of two-spin and four-spin time-correlation functions, such as 〈Siz(t)Sjz〉 and 〈Siz(t)Sj+(t)SkzSl−〉, for finite linear chains with periodic boundary conditions containing as many as ten spin-½ particles coupled by a nearest-neighbor Heisenberg exchange interaction. Previous workers have computed thermodynamic properties of finite linear chains, but this to our knowledge is the first calculation of time-dependent properties, which requires the eigenfunctions as well as eigenvalues. Determination of the correlation functions enables us to compute the variation of magnetic-resonance linewidth with frequency in a linear-chain salt such as Cu(NH3)4SO4·H2O by applying the methods of Kubo and Tomita. Values of linewidth computed with our exact correlation functions give very much better agreement with Rogers' experimental values for Cu(NH3)4SO4·H2O than the usual Gaussian approximation. We also show results for the simple two-spin correlation function, such as measured by inelastic neutron scattering. Its frequency transform is non-Gaussian, showing a steep rise near zero frequency.
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.
Low-Lying Crystal-Field Spectra of Rare Earth Compounds
Authors: Bloor D. , Ellis E. , Martin D. H. , Wadham A.
Published: February 2004

The crystal-field splitting of the degenerate ground state of rare earth ions produces energy differences which correspond to far-infrared frequencies (10–200 cm−1). Absorption spectra of certain rare earth double nitrates, ethyl sulphates, and oxides, cooled to liquid helium temperatures, have been observed in this frequency range. The positions of the absorption lines have been compared with values deduced from optical and other measurements. In general the agreement is good. Measurements of linewidths with different concentrations of paramagnetic ions indicate that spin-lattice relaxation and electric quadrupole interaction are the predominant line-broadening mechanisms. In the case of Pr3+ in La ethyl sulphate splitting of non-Kramers degenerate levels leads to further broadening. The splitting of the crystal-field levels of Er2O3 in the antiferromagnetic state have been observed, but not yet fully analyzed.
Infrared Zeeman Effect for Ce3+ in LaCl3
Authors: Bagguley D. M. S. , Vella-Coleiro G.
Published: February 2004

The Zeeman splittings of the lowest 2F5/2 and 2F7/2 levels for Ce3+ in LaCl3 have been investigated in fields up to 200 kG at 77° and 27°K. The results obtained at 27°K are compared with the predictions from crystal-field theory.
Interaction Constants in CeCl3
Authors: Landau D. P. , Birgeneau R. J. , Hutchings M. T. , Wolf W. P.
Published: February 2004

Results of EPR measurements on Ce3+ pairs in LaCl3 are combined with susceptibility and specific-heat measurements on single crystals of CeCl3 to obtain estimates of the eight parameters which characterize the interactions between nearest and next nearest Ce3+ neighbors. It is found that the major part of the interactions can be accounted for by magnetic dipole-dipole and second-order electric quadrupole-quadrupole couplings, but there is evidence for some additional effects such as anisotropic exchange or higher-order electric multipole interactions. The dominant term is an antiferromagnetic Ising coupling between nearest neighbors, which form linear chains along the c axis. This suggests a simple ordered state for CeCl3, which has been observed to undergo a single sharp transition at 0.27°K. However the coupling between neighboring chains is complicated by cancellations resulting from the high symmetry of the cation lattice and the problem of long-range order is found to be similar to that in the antiferromagnetic triangular Ising model, for which no simple ground state can be predicted although all the interactions are known.
EPR in the Excited Optical States of Exchange-Coupled Chromium Ion Pairs in Ruby
Authors: Imbusch G. F. , Graifman M. B.
Published: February 2004

By means of an optical detection technique, we have studied EPR in the excited metastable optical level of exchange-coupled chromium ion pairs in ruby with concentration of ∼0.2% Cr2O3. In such excited pair states one ion is in an excited optical state while the other is in its ground state. We have confined our attention mainly to fourth-nearest-neighbor pairs. We find evidence that when one ion of the pair is excited, it is antiferromagnetically coupled to its fourth-nearest-neighbor, while both ions are ferromagnetically coupled in the ground state. In the optical detection method we monitor the fluorescence from the particular center being studied and note the change in fluorescence signal which occurs when resonant microwave power changes the population in the excited state. Besides the resonance signals expected from our knowledge of the excited pair state, we find a number of additional resonances. Some of these have been identified as single chromium ion resonances which affect the pair fluorescence because of the transfer of optical excitation from single ion to pair. The other signals appear to be fourth-nearest-neighbor ground-state resonances which are detected because of their effect upon the optical pumping of the pair.
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.
Magnetic-Shape Anisotropy in Polygonal Prisms
Authors: Hagedorn F. B. , Gyorgy E. M.
Published: February 2004

It is shown that only a uniaxial magnetic shape anisotropy can be exhibited by a body of arbitrary shape if the applied magnetic field (H) is large enough to make the magnetization uniform throughout the sample. A square plate will accordingly be isotropic around an axis perpendicular to the plate but uniaxial around any other axis. The purpose of this paper is to emphasize this aspect of shape anisotropy for very high fields and to illustrate the anisotropies which are observed experimentally for several polygonal prisms using typical laboratory values of H. Two interesting examples are equilateral triangles and squares cut from thin plates, which when measured with H in the plane of the plates, yield torque curves of sin6θ and sin4θ, respectively. It is also demonstrated that the easy axes for a cube are the cube edges for fields less than about 6Bs but become face diagonals for larger fields. For thin square plates, the easy axes are diagonals for fields less than about 11Bs but are square edges for larger fields. For a square sample whose height is 0.8 of the square edge, the easy axes reorient for fields near Bs by splitting on either side of the square edges, giving sin8θ components, and then rotating to the diagonals with increasing field. Rotation of the easy axes has not been observed in any of the triangular samples. Although a large reduction in shape anisotropy occurs as large fields are applied, appreciable anisotropy remains at fields as large as 15Bs for some of the samples studied. Experimental anisotropy values are given as a function of H/Bs for several regular polygonal prisms.