bluuebunny/crossref_metadata_2025_split huggingface dataset:
Dipolar Corrections to the Magnon Energy in the Band Theory of Ferromagnetism
Authors: Morkowski Janusz 
Published: January 2006

The magnon energy spectrum in the itinerant d-electron model of ferromagnetism is calculated, taking into account the dipolar interaction of magnetic electrons. The model of band ferromagnetism is considered in which the intra-atomic interband exchange provides the dominant interaction of magnetic electrons. The case of two degenerate bands is discussed and the effective mass approximation for the one-electron energy is adopted.
In the long-wavelength limit, the energy of magnons is given by a formula closely resembling the one derived by Holstein and Primakoff for the Heisenberg model of ferromagnetics. The differences consist, first, in replacing the Heisenberg exchange parameter by a quantity which depends not only on the exchange splitting of spin − and spin + electrons, but also on the applied magnetic field, and second, in the presence of small corrections due to the magnetic form factor of the d electrons.
Magnetic Structures and Phase Transformations in Mn-Based CuAu-I Type Alloys
Authors: Pál L. , Krén E. , Kádár G. , Szabó P. , Tarnóczi T. 
Published: January 2006

Investigations of the magnetic properties in the ordered CuAu-I-type manganese alloys are reviewed. The formation of the ordered phase and the possible magnetic structures are discussed. New experimental results for the Mn-Ni, Mn-Pd, and Mn-Pt systems are reported.
Neutron diffraction shows the basic antiferromagnetic structure to be the same for all the alloys investigated. In MnPt a magnetic-structure transformation has been observed. Below 800°K the magnetic moments turn from the basal plane gradually to the tetragonal axis. The variation of the transition temperature in the Mn-Pt system as well as that of the Néel temperature in the Mn-Ni, Mn-Pd, and Mn-Pt systems with concentration were measured and are theoretically analyzed.
The dependence of lattice parameters on concentration and temperature was determined. The lattice parameters suffer a significant but continuous change near the Néel temperature which is attributed to Mn-Mn exchange interaction.
Magnetic susceptibility measurements support the neutron-diffraction results. The increase in susceptibility, observed by several authors at lower temperatures, is found to be a result of contaminations.
Enhanced Susceptibilities and NMR Relaxation Rates in Co-Rh Alloys
Authors: Walstedt R. E. , Sherwood R. C. , Wernick J. H. 
Published: January 2006

Dilute alloys of Co in Rh show a weakly temperature-dependent susceptibility increase Δχ (Co) ∼20×10−4 emu/mole of Co solute as compared with χ∼1×10−4 emu/mole for pure Rh. This effect is thought to be associated with Coulomb enhancement of the d-electron spin susceptibility in the neighborhood of the Co impurity. By plotting the 9Co NMR shift vs Δχ (Co) one finds an effective core-polarization hyperfine field considerably smaller than that of Co metal.
Spin-echo double-resonance studies of these alloys show that the nearest-neighbor 103Rh nuclei to the Co impurity undergo a negative NMR shift of ∼0.56% relative to the bulk 103Rh nuclei. The origin of this shift is not clearly understood. In particular, attributing such a shift to d-spin polarization is not consistent with the short-range polarization effects expected.
Measurements of T1 and T2 show strongly enhanced hyperfine field fluctuations at the 59Co nucleus, presumably due to local Coulomb interactions. We find T1T = 39.5 msec°K and T2T = 3.0 msec°K for temperatures ranging from 1.2° to 20.4°K. The discrepancy between T1 and T2 (spin lattice) is apparently a consequence of strong first-order quadrupolar broadening of the 59Co Zeeman levels for | m | &gt;12.
Faraday Rotation in YIG and TbIG
Authors: Cooper R. W. , Crossley W. A. , Page J. L. , Pearson R. F. 
Published: January 2006

Measurements of the Faraday rotation in YIG and TbIG have been made as a function of temperature in the range 100°–450°K at the helium-neon laser wavelength of 1.15 μ. This wavelength lies on the edge of the YIG window at the short-wavelength absorption limit. Measurements were made on single-crystal blocks of YIG and TbIG up to 7 mm thick in applied fields of up to 10 kOe.
In YIG the major contribution to the Faraday rotation at this wavelength is the dispersive part associated with absorption bands in the visible and near ir. This contribution reaches a maximum of 188°/cm at 280°K and can be fitted to the sublattice magnetization data of Anderson. For TbIG we find αF = 448°/cm at 300°K and a very strong temperature dependence. In addition we observe a field-dependent Faraday rotation of −3.8°/cm/kOe at 300°K. Extrapolation of the observed rotations to zero internal field removes he discontinuity in | αF | which otherwise appears at the compensation temperature (245°K). The zero-field Faraday rotation may be analyzed in terms of three contributions: a nondispersive part arising from the exchange resonance, a dispersive part arising from the Fe3+ sublattices, and a dispersive contribution from the Tb3+ sublattice. Additional information on the Tb3+ contribution was obtained from Verdet constant measurements on TbGaG and TbAlG.
Transverse Kerr Magneto-optical Effect in EuO Films
Authors: Suits J. C. , Ahn K. Y. 
Published: January 2006

Kerr magneto-optical measurements in the transverse orientation were made on ferromagnetic EuO films. These films were cooled to approx 10°K and measured immediately after deposition without exposing the films to air. For incident light polarized in the plane of incidence, the change in intensity of reflected light upon reversal of the magnetization, δ = ΔI/I0(I0 = reflected light intensity for a demagnetized sample), is large; at a wavelength of 800 mμ, δ = 30%. This may be compared with iron which exhibits a maximum δ ≈ 1% for wavelengths in the visible. Incident light polarized perpendicular to the plane of incidence shows no effect (δ = 0±1%).
The transverse Kerr effect exhibits a strong dependence upon wavelength: δ is small at 400 mμ, increases to a maximum at 500 mμ, changes sign at 600 mμ, increases to a maximum at 800 mμ, and then gradually diminishes in magnitude at longer wavelengths.
By measuring the phase change as well as the intensity change in the transverse Kerr effect, it is possible to derive experimentally the real and imaginary components of the off-diagonal element of the complex dielectric tensor. Measurements of the longitudinal Kerr effect and Faraday effect in EuO films are discussed in terms of these tensor components.
Magnetostriction of Dilute Dysprosium Iron and of Gadolinium Iron Garnets
Authors: Clark A. E. , Rhyne J. J. , Callen E. R. 
Published: January 2006

λ γ,2 and λε,2 have been measured on a series of partially substituted DyxY1−xIG single crystals between 4.2° and 300°K and in fields up to 110 kOe. Because of the ground-state configuration of the Dy3+ ion (6H15/2) in the crystal field, DyIG has a large magnetostriction. However, since the exchange field on the rare-earth ion is small (Hex ≈ 300 kOe), this magnetostriction is large only at low temperatures. The 4.2°K magnetoelastic energies of the Dy3+ ion in the garnet are: Bγ,2 = λγ,2/2(C11–C12) = − 830 cm−1 and Bε,2 = λ111/4C44 = −1090 cm−1 which are in fact the same order of magnitude as the large energies observed in dysprosium metal. The magnetostriction is found to be linear in Dy concentration, establishing a single-ion source of the magnetostriction. Since the rare-earth exchange field is relatively small, the forced magnetostrictions are extraordinarily large and λ actually decreases from a large value to zero with increasing field strength whenever the iron moment dominates (x &lt; 0.25). To understand these large and unusual temperature and field dependences, crystal-field effects, which affect λγ,2( = 32λ100) and λε,2( = 32λ111) differently, are essential.
The magnetostriction in fully substituted GdIG at low temperatures has also been measured. Since the ground state of Gd3+ has zero orbital angular momentum, only a small magnetostriction is expected. This is indeed observed and the magnetostriction of GdIG is of the same magnitude as that of YIG. In particular, at 4.2°K, the contribution of Gd3+ to λγ,2 is 12×10−6, and to λε,2 is 1.8×10−6.
Single-Ion Models and the Temperature Dependence of Magnetostriction and Piezomagnetism
Authors: White R. L. , Phillips T. G. 
Published: January 2006

We have recently demonstrated that the 0°K magnetostriction and piezomagnetic constants of various magnetic insulators can be predicted approximately, using a single-ion model and a microscopic single-ion magnetoelastic tensor, Tijklσ, determined from the strain dependence of EPR spectra. The model leads to a natural classification of the magnetoelastic constants depending on whether their microscopic origin is in the strain dependence of a g tensor (Fijkl = ∂gij/∂εkl) or of a crystal-field energy (Gijkl = ∂Dij/∂εkl). The identification of microscopic origin also allows a prediction of the temperature dependence of the magnetoelastic constants since it identifies the relevant spin components and the power to which they are raised in the approximate Hamiltonian.
The magnetostriction constants of most materials will vary (in the low-temperature region) as [M(T)/M(0)]3. For heterogeneous ion compounds such as the garnets, however, when the principal magnetostrictive mechanism is the strain dependence of the g tensor, the magnetostriction may vary as [MRE(T)/MRE(0)]×[MFe(T)/MFe(0)], e.g., YbIG. For most piezomagnetic materials the piezomagnetic constants will vary as [M(T)/M(0)], as in CoF2; cases exist, however, where more complicated temperature dependence is to be expected, for instance in the rare earth orthoferrites.
Neutron-Diffraction Data on Ti2O3 and V2O3
Authors: Kendrick H. , Arrott A. , Werner S. A. 
Published: January 2006

Without considerable care one might conclude from neutron-diffraction studies of Ti2O3 and V2O3 that these materials are antiferromagnetic. The problem is that multiple-Bragg scattering can masquerade as small superlattice reflections. We have noted a large and rapid change in the intensities at the superlattice positions when the crystal is tilted about the scattering vector, indicating multiple scattering. The intensities of these reflections relative to the nuclear reflections decrease with increased collimation.
In order to reduce this source of scattering, we have used a 2.09 Å beam instead of the usual 1.07 Å neutrons. Energy analysis of the beam reflected from the superlattice positions gives the result that there is essentially no real magnetic scattering at either the (111) or the (100) in Ti2O3. We can put an upper limit of 0.01 μB to Néel-type antiferromagnetism.
Investigations of a single crystal of V2O3 above the phase transition (∼150°K) were subject to the same problems. However, below the transition, the mosaic structure of the crystal increased (indicating that the crystal was broken up) and there remained no detectable intensity at the superlattice positions.
Anomalous Magnetic Properties of Ti5O9
Authors: Keys L. K. 
Published: January 2006

A magnetic susceptibility study from 77° to almost 900°K and an electron-spin-resonance study from 77° to 160°K of Ti5O9 shows an anomalous magnetic behavior. The magnetic susceptibility gives a peak in its temperature dependence which resembles a Néel temperature and can be interpreted to indicate antiferromagnetic-like behavior. The magnetic susceptibility peak occurs at about 130°K. An x-ray study of Ti5O9 indicates face sharing anion octahedra with a short metal-metal distance which lends support to a cation-cation interaction model.
The electron-spin-resonance (ESR) study gives spectra which yield g values of 1.98±0.02. This indicates little orbital contribution to the magnetic moment. The spectral linewidth increases sharply with increasing temperature in the region of the magnetic susceptibility maximum, showing effects of electron-phonon interactions. The signal intensity decreases rapidly above this susceptibility peak. The line shape is asymmetric below this temperature region, however, it becomes symmetrical above it.
The behavior presented in these results reflects a complex effect undoubtedly involving delocalized electrons in which a low-temperature electron localization may occur. The value of the magnetic moment of Ti3+ in Ti5O9 is, therefore, not clear. While some of these results indicate an apparent antiferromagnetic behavior and appear to support the cation-cation interaction model, they cannot be completely resolved as such. The crystalline distortion present may contribute to the trapping of the electrons at low temperatures, and thus facilitate the cation-cation interactions and influence the spin-lattice relaxation times.
Fiber-Reinforced Fe-50Ni and Fe-1.35Si Alloys
Authors: Colling D. A. 
Published: January 2006

The feasibility of employing fiber reinforcement in order to strengthen soft magnetic materials for high-temperature applications has been investigated. Specimens of Fe-50Ni and Fe-1.35Si containing tungsten fibers (0.003 to 0.010 in. in diameter) in concentrations up to 17.3 vol % were prepared by hot rolling laminations which were encapsulated in a mild steel “envelope”.
Short-time tensile properties, saturation induction, and coercivity were measured at ambient and/or elevated temperatures. The tensile stress-strain behavior was consistent with the theory for composites containing continuous fibers aligned parallel to the tensile axis. Saturation induction was found to follow the simple dilution law at all temperatures up to the Curie point, being equal to the product of the matrix saturation and volume fraction of matrix in the composite. An anisotropy was observed in coercivity, dependent on the fiber direction with respect to the applied field. In all cases, the measured Hc was higher when the field was normal to the fiber direction and the difference increased with increasing fiber concentration.
Investigation of Ferrimagnetism in Some Compounds using Polarized Neutrons
Authors: Murthy N. S. Satya , Begum R. J. , Somanathan C. S. , Natera M. G. 
Published: January 2006

Polarized neutrons offer a very useful method of studying ferrimagnetic materials such as ferrites, in which the multiplicity of cations and their valence states prevent a unique determination of the spin structure when only polycrystalline material is available. This paper presents the first extensive use of polarized neutron powder-diffraction patterns for determining the structure of a carbide of Mn and Co and of a number of mixed ferrites having the spinel structure.
The ferrimagnetic carbide with composition (Mn,Co)4C is found to have a cubic structure of the Mn4N type, with one of the Mn atoms at the cube corner and the face centers being occupied by one Mn and two Co atoms in a statistical distribution. The two Mn atoms are antiferromagnetically aligned with respect to each other, the corner atom having a moment of 4.0 μB while the face center moment is 3.0 μB. The two Co atoms have a moment of 0.8 μB each and are aligned parallel to the corner Mn moment along the cube edges. The material has a Néel temperature of 810°K and saturates at a field of 4.5 kOe. Polarized neutrons were used to choose a structure of cubic symmetry in preference to one of tetragonal symmetry.
Two mixed ferrite systems of the general formula MxM′1−xFe2O4 where M = Mg, Zn and M′ = Mn, Ni have been studied for various values of x. Their Néel temperatures and cation distributions have been determined.
NMR of 53Cr and 77Se in Ferromagnetic Chalcogenide Spinels
Authors: Berger S. B. , Budnick J. I. , Burch T. J. 
Published: January 2006

The NMR of 53Cr nuclei has been observed in ferromagnetic CdCr2Se4, CdCr2S4, and HgCr2Se4 at 4.2°K using spin-echo and cw techniques. The spectra are complex with a principal triplet and have been analyzed considering coaxial anisotropic hyperfine and electric quadrupole fields of comparable magnitude to be acting on the chromium nuclei in randomly oriented domains. An excellent fit has been obtained between the calculated spectrum and spin-echo data. For CdCr2Se4, CdCr2S4, and HgCr2Se4, the separation between the outer components of the triplet is 1.76, 1.90, and 1.96 MHz, the isotropic part of the hyperfine field is −182.6, −191.0, and −178.3 kOe and the anisotropic component of the hyperfine field is +2.33, +2.07, and +2.3 kOe, respectively. The signs of the hyperfine field components indicate their direction with respect to the magnetization and were determined by measuring the frequency shift with applied magnetic field.
The NMR of 77Se nuclei has also been observed in HgCr2Se4 and CdCr2Se4 at 4.2°K. The spectra are consistent with the model of randomly oriented domains and exhibit a strongly anisotropic hyperfine field. The origin of the spectra and the sign of the hyperfine field components were determined by measuring the frequency variation of the spectra with applied magnetic field.
Neutron-Diffraction Study of the Ferromagnetic Mixed-Anion Spinel CuCr2Se3Br
Authors: White J. G. , Robbins M. 
Published: January 2006

A new class of mixed-anion spinels has been prepared. These compounds have the general formula Cu[Cr2]X3Y where X = S2−, Se2−, Te2− and Y = Cl−, Br−, I−. The materials are ferromagnetic with TC (Curie temperature) close to room temperature. A neutron-diffraction study was made of CuCr2Se3Br which is a cubic spinel with a0 = 10.416 Å and TC = 274°K. The observed magnetic moment was 5.25 μB at 4°K and a field of 10 kOe.
Neutron-diffraction measurements were made at room temperature and at liquid nitrogen temperature (T/TC = 0.285). From the room-temperature data the material was found to be a normal spinel with u = 0.389±0.002. The low-temperature data showed magnetic scattering which was evaluated in terms of simple models: (a) a spin arrangement corresponding to Cu1+[Cr23+]Se3Br having zero moment on the A sites and a moment of 6 μB on the B sites, (b) a ferrimagnetic arrangement corresponding to Cu2+[Cr3+Cr2+]Se3Br with 1 μB on the A sites and 7 μB on the B sites. The first model gives very good agreement with the experimental data while model (b) is quite incompatible with the data.
Enhanced Effective Exchange Interaction due to Localized Spins in Dilute Alloys and Rare Earth Metals
Authors: Kim D. J. 
Published: January 2006

An effective interaction between conduction electrons is obtained by eliminating the exchange interaction between conduction electrons and localized spins in metals both in the paramagnetic and spin-ordered state. In the paramagnetic state the effective electron interaction is mediated by the flipping motion of the localized spin under the action of the local field and the electron interaction derived is of an exchange type and repulsive in the vicinity of the Fermi surface. On this basis we show that the observed ferromagnetism in dilute alloys like Fe in Pd may be understood from the large enhancement of conduction-electron susceptibility.
In the spin-ordered state, such as rare-earth metals below the Curie temperature, the effective electron interaction arises from the exchange of spin waves between electrons. The electron interaction obtained is of a form of repulsion between electrons of opposite spins at the same atomic site in the vicinity of the Fermi surface. The electron self-energy due to this effective electron interaction is calculated for a simplified model and we discuss the possibility of an appreciable enhancement of the electronic specific heat in rare earth metals.
On the Theory of Anomalous Tunneling due to Paramagnetic Impurities
Authors: Solyom J. , Zawadowski A. 
Published: January 2006

Recently some anomalies have been observed in the characteristics of tunnel diodes at zero bias. Anderson and Suhl have called attention to the resonance scattering of electrons on paramagnetic impurities in the oxide layer. The effective density of states appearing in the formula of tunnel current is determined and the tunnel current is calculated by summing up the contributions of resonance scatterings.
The actual appearance of the effect varies greatly and is strongly dependent on the parameter values: (1) For ferromagnetic coupling: resistivity minimum at zero bias, relative amplitude: 0–0.2. (2) For antiferromagnetic coupling: (a) giant resistivity maximum at zero bias, relative amplitude 0–100; (b) local resistivity minimum at zero bias superimposed on a background curve with resistivity maximum [type 2 (a)].
The investigation of tunneling characteristics may be a powerful method to check the resonance scattering amplitude for paramagnetic impurities.
Dynamic Susceptibilities of Transition Metal Alloys
Authors: Lederer Pascal , Mills D. L. 
Published: January 2006

In this paper, we study dynamical properties of transition metal alloys by examining the form of the frequency and wavevector-dependent magnetic susceptibility within the framework of a simple molecular-field approximation. We describe the metal by a simple one-band model, in which two d electrons in the atomic cell i interact via the intra-atomic Coulomb interaction Ui, which differs from the value in the host if i refers to an impurity site. The impurity also is supposed to produce a local change in crystal potential.
In the general case, an expression for the susceptibility is derived in the form of an N×N matrix, where N is the number of lattice sites. When applied to a pure metal, the result reduces to the expression obtained previously by Izuyama, Kim, and Kubo.
Some applications of the results to the one-impurity problem are considered. In particular, in the case where a magnetic moment has formed in the impurity cell, a description of the electron spin-resonance of the impurity center is obtained.
A discussion of properties of Pd-Ni alloys is presented. The expression obtained for the magnetic susceptibility allows a calculation of the contribution to the electrical resistivity from s-d spin flip scattering. The recent resistivity measurements of Schindler and Rice are interpreted with the results.
Measurements on Lithium Ferrite Crystals having Near-Zero Defect Concentrations
Authors: Spencer E. G. , Lepore D. A. , Nielsen J. W. 
Published: January 2006

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