bluuebunny/crossref_metadata_2025 huggingface dataset:
The Magnetic Susceptibility and Specific Heat of Nearly Ferromagnetic Ni-Rh Alloys
Authors: Brinkman W. F. , Bucher E. , Williams H. J. , Maita J. P.
Published: January 2006

Recently, we reported the observation of the effective mass enhancement due to spin fluctuations in Rh-Ni alloys close to the critical concentration for the onset of ferromagnetism. In this paper we present the complete experimental data giving the specific heat and susceptibility as a function of temperature for a number of alloys near the critical concentration. We also present a qualitative comparison of these results with the theoretical predictions.
The Pure Pd Problem
Authors: Foner S. , Doclo R. , McNiff E. J.
Published: January 2006

Magnetic-moment measurements vs field and temperature are presented for both Pd and Pt. An extreme sensitivity of χ for Pd at low T has been observed and the conditions for unambiguous measurements of χ at low T are discussed. Results for Pt show an analogous sensitivity to trace amounts of impurities and indicate a maximum in the susceptibility near 100°K. Brief comments concerning estimates of exchange enhancement by means of high-field measurements are also made.
Nuclear Magnetic Resonance in Palladium-Silver Alloys
Authors: Narath Albert
Published: January 2006

The 109Ag NMR has been studied in a series of Pd1−xAgx alloys by spin-echo techniques in external fields near 55 kOe and at temperatures of 1°–4°K. Knight shifts (K), spin-lattice (T1), and spin-spin (T2) relaxation times were determined for 12 compositions in the range 0.025≤x≤1. The shifts are negative for x≤0.35. From the observed lineshape in the x = 0.025 alloy (K = −1.41%) it is estimated that K = −1.46% in the limit of infinite dilution. After adjustment for an estimated direct contact shift of +0.34%, this value yields a hyperfine field of −140(±10) kOe/μB of palladium d-spin magnetization, which presumably arises from spin polarization of the s conduction electrons by the palladium host. This process is found to be ineffective as a spin-lattice relaxation mechanism. The observed relaxation times T1T increase gradually from a value of 9.6(±0.5) sec·°K for pure silver to a broad maximum of 26(±3) sec·°K near x = 0.3 and remain nearly constant at lower concentrations [T1T = 22(±4) sec·°K for x = 0.025]. The variation of (T1T)−1/2 with composition is qualitatively consistent with the expected variation of the s electron density of states at the Fermi level. The 105Pd spin-lattice relaxation times in palladium metal have been remeasured with the result T1T = 0.7(±0.2) sec·°K.
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 | >12.
Electronic Structure of Platinum and Palladium Alloys
Authors: Froidevaux C. , Launois H. , Gautier F.
Published: January 2006

The electronic structure of some dilute alloys of Pd and Pt is studied in relation with the band structure of the pure metals (PdRh, Ru… PtIr, Re…). We qualitatively discuss the magnetic susceptibility and specific heat measurements taking account of the band-structure effects (deviation from the rigid-band model) and of the exchange-enhancement effects. We point out that NMR measurements allow the determination of the local susceptibility on the impurity site and of its exchange enhancement factor as shown by new experimental results on Pt-Ir alloys.
The Electron-Phonon Scattering Contribution to the Anomalous Magneto-optical Effects in Ferromagnetic Metals
Authors: Kondorsky E. I. , Vediaev A. V.
Published: January 2006

The expression for the parts of off-diagonal elements of electrical conductivity which are related with anomalous Hall and magneto-optics effects in pure ferromagnetic metals have been found using the methods of thermodynamic diagram technique. It was the electron-phonon scattering mechanism that has been taken as one that is responsible for frequency-dependent terms in the expression of imaginary parts of the off-diagonal elements mentioned above. The calculations have been done for the frequency interval that is not very close to the frequency corresponding to the interband transitions. In this particular case the character of a frequency dependence of the given part of electrical conductivity at low temperatures has been determined and the maximum of its imaginary part near the Debye frequency predicted.
The Faraday Effect in Garnets in the Infrared Region
Authors: Chetkin M. V. , Shalygin A. N.
Published: January 2006

The temperature dependence of the Faraday effect in TbIG was investigated in the infrared where the rotation αφ does not depend on frequency. It was shown that besides the change in the sign of αφ at the compensation point, there is another change in the sign of αφ at T = 110°K. The temperature dependence of αφ agrees qualitatively with its theoretical behavior obtained in the infrared region from the off-diagonal components of permeability tensor [μ]. For the quantitative agreement of the theoretical and experimental values of αφ, it is necessary to assume that the g-factor of Tb3+ diminishes at low temperatures. The temperature dependence of the g-factor of the Tb3+ ion in TbIG was determined, It was shown that in Bi0.24Ca2.76Fe3.62V1.38O12 at λ > 4 μ the Faraday effect is positive and independent of λ. The Faraday effect in the garnet has different signs in the infrared and visible regions. This fact is in accordance with the exchange mechanism of the Faraday effect observed in garnets in the infrared.
Magneto-optic and Magnetic Properties of NdCo5, Nd2Co17, and Co Films
Authors: Stoffel A. M.
Published: January 2006

NdCo 5 , Nd2Co17, and Co films have been prepared by vapor deposition in ultrahigh vacuum using the alternate layer deposition technique. The substrates were held at −116°C during deposition. A subsequent heat treatment caused a diffusion of the layers and formed the intermetallic compounds. Direct-current Kerr hysteresis loops were plotted during the anneal. The coercive force was measured as a function of temperature to determine when the diffusion was completed. It was found that the films had to be heated above 600°C to form the compounds. At 25°C all films exhibited large coercive forces of 535, 270, and 210 Oe for NdCo5, Nd2Co17, and Co, respectively, but Hc decreased rapidly with increasing temperature. X-ray analysis indicated that all films had a strong fiber texture with the c axis normal to the film. It is assumed that isotropic planar stress and a perpendicular anisotropy cause the high coercive forces at lower temperatures. For all films the optical constants n, k, and the Voigt parameters Q0 and q were measured in vacuo below 10−9 Torr in the wavelength range 400–650 mμ. (Q0 and q are the modulus and the phase of the complex quantity Q which is the off-diagonal component of the complex permittivity tensor.) These measurements show that with increasing rare-earth content the magneto-optic amplitude Q0 decreases.
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.
Magneto-optical and Nuclear Magnetic Resonance Studies of RbNiF3
Authors: Smolensky G. A. , Pisarev R. V. , Petrov M. P. , Moskalev V. V. , Siny I. G. , Judin V. M.
Published: January 2006

The Faraday rotation (FR), magnetic circular dichroism (MCD), magnetic linear dichroism (MLD) and nuclear magnetic resonance (NMR) have been studied in the transparent ferrimagnet RbNiF3 (TC = 139°K). It was found that MCD and asymmetric anomalous dispersion of FR may be explained by the exchange splitting of electronic states of Ni2+ ions below TC. The structure and the temperature dependence of MCD of A23→1Ea transition confirms the model of magnetic structure with two unequivalent antiferromagnetically aligned sublattices. For the first time on the basis of NMR results the existence of two oppositely directed sublattices at temperatures about 100° above TC was observed in external magnetic field. The magnetization of one sublattice changes sign at T≃270°K.
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.
New Methods of Magneto-optical Signal Modulation and Detection
Authors: Smith D. O.
Published: January 2006

Methods of modulating magneto-optical signals are useful in improving the signal-to-noise ratio of practical systems. Using the longitudinal or polar magneto-optical orientation and incident light polarized out of the plane of incidence (say at 45°), an intensity-modulated magneto-optical signal can be generated by modulating the phase of the component of light which is ‖ (or ⊥) to the plane of incidence. No analyzer is required with the consequence that this type of modulation can be used in fully focused light if axial symmetry is maintained. Signal modulation can also be obtained by thermal modulation of the magnetic material. For a 1-μ-diam region of a thin film the frequency response is calculated to be ∼500 MHz. Various magneto-optical configurations are readily devised which yield the value of a bit (1 or 0) in terms of the phase (0 or π) between the magneto-optical signal and the electron-beam intensity modulation. If the thermal modulation is effected by an electron beam, the need for a high-resolution optical deflector is eliminated in a high-bit-density computer-memory application.
The Magnetostriction Behavior of Iron Single Crystals
Authors: Williams G. M. , Pavlovic A. S.
Published: January 2006

The magnetostriction of iron single crystals has been measured as a function of temperature (77°K to 900°K), magnetic field (up to 14 kOe), and magnetic field orientation. These data have been used to evaluate the magnetostriction constants for two- and five-constant expressions. The high-temperature maximum in λ100 as reported by Tatsumoto and Okamoto has been confirmed but not the low-temperature maximum. A comparison of the five constants with the conventional magnetoelastic coupling theory revealed no correlation. The forced anisotropic magnetostriction constants have been evaluated as a function of temperature and found to be small for iron, while the volume effect was in agreement with previous results.
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 < 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.
Magnetostriction of Paramagnetic Transition Metals and Alloys
Authors: Fawcett E. , White G. K.
Published: January 2006

Measurements of the longitudinal magnetostriction of transition metals and alloys in groups IV, V, VI, and VIII are reported. With the assumption that the magnetostriction is isotropic the volume-dependence of the magnetic susceptibility is evaluated. A theoretical estimate of the volume-dependence of the orbital susceptibility, ∂ lnχorb/∂ lnV≃1.5 (≃ electronic Gruneisen parameter), agrees well with the measured values for the group V metals. The group IV and VI metals appear to have a linear magnetostriction, though the field-independent susceptibility of a paramagnetic metal would indicate a quadratic magnetostriction as observed in the group V and VIII metals. The negative magnetostriction of Pd, Pt, and their alloys indicates that the exchange interaction decreases with increasing volume. But it is not possible to estimate theoretically the magnetostriction of these and other group VIII metals and alloys since too many unknown factors are involved. The emiprical relation between susceptibility and electron density also fails to predict correctly the magnetostriction.
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.
Thermal Expansion and Forced Magnetostriction in a Terbium Single Crystal
Authors: Alberts L. , du Plessis P. de V.
Published: January 2006

Forced magnetostriction and thermal-expansion measurements on a terbium single crystal are reported. The isotropic component of the basal-plane forced magnetostriction is evaluated for applied fields between 17 500 and 19 500 Oe. A peak value of −18.5×10−8/Oe is found at 246°K. Large, positive, field-dependent forced-magnetostriction values are obtained along the 〈0001 〉 axis for fields applied along the 〈1010〉 axis. The field dependence of the 〈0001 〉-axis forced magnetostriction is in agreement with Belov's thermodynamic description in the vicinity of the Curie temperature. A large negative expansion anomaly of − 104×10−6/deg is obtained at 224°K. The magnetic component of this strain is identificed with the exchange and ordinary magnetostriction, and not only with an ordinary term as was done by Rhyne and Legvold. The large magnetothermal strain of 900×10−6 occurring at the Curie point, and the persistence of the anomalous behavior high in the paramagnetic region can be ascribed to the exchange magnetostriction. Using 〈0001 〉-axis forced strain measurements, a calculation by Belov's method of thermodynamic coefficients yields a value of −47×10−6 /deg at the Curie point.
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.
Studies of Curie-Point Increases in EuO
Authors: Shafer M. W. , McGuire T. R.
Published: January 2006

The ferromagnetic transition temperature (TC) of EuO has been increased from 69° to 135°K by selectively doping to increase the electrical conductivity. Three different chemical systems have been studied: the EuO-Eu, the EuO-Eu-RE2O3, and the EuO-RES systems (RE is a rare earth other than europium). Compositions in the latter system were multiphase because the solubility of the rare-earth sulfides in EuO is very small and it was necessary to add about 10% to cause significant Curie-temperature increase. Single crystals have been grown from ternary compositions in the EuO-Eu-RE2O3 system with magnetizations at 77°K as high as 170 G cm3/g and ferromagnetic Curie temperatures (TC) close to the paramagnetic θ values, a condition not observed in the other doped europium chalcogenides. The effect of the Eu metal on the formation of these crystals and its role in “forcing” the trivalent rare-earth oxide into the rock-salt lattice is discussed. From Kerr measurements and the optical absorption data it is shown that the magnitude of the rotation of the doped material at 80°K is equal to that of pure EuO at 18°K. This makes this material attractive for use in magneto-optical devices operating at nitrogen temperature.
Magnetic Oxides Crystallizing in the Rutile Structure
Authors: Villers G. , Gibart P. , Druilhe R. , Burlet P.
Published: January 2006

Mixed oxides Cr1−xMnxO2(0 ≤ x ≤ 0.7) were prepared in powder form. Measurements of resistivity versus temperature and of the optical absorption edge point to semiconductor-like behavior. The field dependence of magnetization is linear from 7 to 20 kOe. Variation of the mean number of Bohr magnetons as a function of x and neutron diffraction experiments suggest a canted spin structure.
The Magnetic and Crystallographic Properties of MnAs0.92P0.08
Authors: Ridgley D. H. , Geisman J. H.
Published: January 2006

The magnetic and crystallographic properties of polycrystalline MnAs0.92P0.08. were studied over a range of temperatures. A gradual distortion of the NiAs to the MnP structure coincides with an anomaly in the susceptibility curve, similar to that found with MnAs. It is suggested that the distortion of the NiAs structure results primarily from anion-anion bonding. The susceptibility anomaly is attributed to an increase in the strength of the antiferromagnetic exchange coupling resulting from a decrease in Mn-Mn separation during distortion. The appearance of metamagnetism at low temperatures is shown to be consistent with this view.
Resistivity and Magnetic Order in Ti2O3
Authors: Van Zandt L. L. , Honig J. M. , Goodenough J. B.
Published: January 2006

Electrical resistivities of pure and vanadium-doped single crystals of Ti2O3 have been measured as a function of applied magnetic field strength and temperature. The anomalous high-temperature increase in electrical conductivity has been confirmed. It is argued that the symmetry of Ti2O3 leads naturally to a two-band model having bandwidths and an energy separation between band centers that are sensitive to the crystallographic axial ratio c/a. With this model, the change in conductivity with temperature can be adequately described on the basis of known variations in the c/a ratio with temperature. The vanadium-doped samples are good p-type conductors and exhibit a negative magnetoresistance at low temperatures. With a model of inelastic scattering at trace impurities carrying a localized magnetic moment, it is possible to describe the negative magnetoresistance of vanadium-doped samples provided the total, local (applied plus intrinsic) magnetic fields are within a few gauss of the applied field. It is concluded that the existence of antiferromagnetic order in Ti2O3 is in doubt and that the resistivity behavior can be readily interpreted without recourse to a magnetic-ordering mechanism.
Magnon Drag at Optical Frequencies and the Infrared Spectrum of MnTe
Authors: Zanmarchi G. , Haas C.
Published: January 2006

A phenomenological theory is given for the interaction of free charge carriers with localized spins in an antiferromagnetic semiconductor. Deviations of the spin system from the normal isotropic equilibrium distribution, induced by the motion of the charge carriers, are taken into account. The theory is used with success for the interpretation of the electrical resistivity, the thermoelectric power (magnon-drag contribution), and the optical properties of the antiferromagnetic semiconductor MnTe.
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.
Development of a Co-W Ferromagnetic High-Temperature Structural Alloy
Authors: Ashbrook R. L. , Hoffman A. C. , Sandrock G. D. , Dreshfield R. L.
Published: January 2006

Rotors for space power generators require a compromise between high-temperature strength and magnetic properties. Rotors must withstand high centrifugal stresses at high temperatures and develop high induction for small exciting fields. Alloys considered for rotors include maraging steels, H-11 steel, and a Co-base alloy, Nivco. This paper discusses work to develop alloys with improved high-temperature strength and good high-temperature magnetic properties. Because Co has the highest Curie temperature of any metal and is a good base for high-temperature alloys, a NASA superalloy Co-25W-1Ti-12Zr-12C was chosen for further study. Modifications of this alloy were screened for magnetic induction (H = 100 Oe) over a range of temperatures. For increasing W, Curie temperature decreased for the base Co-XW-1Ti-12Zr-12C, and Bmax above 1000°F decreased. Below 1000°F, low W alloys show Bmax vs T inflections due to instability of the fcc phase. Stability of the fcc increased with increasing W and Fe. A preferred alloy, Co-712W-212Fe-1Ti-12Zr-12C, was evaluated for magnetic and mechanical properties in cast form and for mechanical properties as sheet. After aging at 1700°F for 72 h, this alloy had a coercive force of 10.5 Oe at 75°F, and a Bmax of 11.5 kG and 19.3 kG at 1200° and 1400°F, respectively. The stress rupture life at 1200°–1400°F was greater than that of the strongest high-temperature commercially available magnetic-structural alloy.
Effect of Dispersoids on Magnetic Properties of Iron, Cobalt, and Nickel
Authors: Towner R. J. , Pavlovic D. M. , Detert K. , Bufferd A. S.
Published: January 2006

Coercive force and saturation induction of cobalt, iron, and nickel, dispersion strengthened with 0.02 to 0.10 volume fraction of alumina or thoria, were measured at temperatures up to 80%–98% of TC. Saturation magnetization values of iron and cobalt at a given temperature level were found to decrease in direct proportion to the volume fraction of nonmagnetic phase present. The temperature dependence of the measured coercive force was interpreted as a cooperative effect of inclusions and internal stress by reference to coercive force values calculated from the equations of Néel. This was particularly apparent in the Hc vs T curve of nickel where the contribution of inclusions was significant in the low-temperature region, whereas stress was an influential factor at all temperatures. Close correlation between measured and calculated Hc was obtained for all three metals containing 0.02–0.025 volume fraction of dispersoid.
Classification of High-Permeability Nickel-Iron Alloys
Authors: Rassmann G. , Hofmann U.
Published: January 2006

Based on known nickel-iron alloys with very high permeabilities and our own systematic studies of ternary nickel-iron-vanadium, nickel-iron-tungsten, and higher systems with metal additions Me = Cu, Cr, Mo, W, V, and others, universally valid concepts will be developed on the relations existing in these alloys between chemical composition, structure, heat treatment, and properties. In the case that the added metals enter into an essentially stronger bond with Ni than with Fe, a rule is presented which connects the chemical composition of the high-permeability alloys with the valency of the added metal. The consequences of this rule are discussed and compared with experiment.
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.
Coercivity and Domain Structure of Silicon-Iron Single Crystals
Authors: Küppers D. , Kranz J. , Hubert A.
Published: January 2006

For an understanding of the characteristic values of the hysteresis of a ferromagnetic material one must find a connection between the magnetic domain structure and the magnetization curve of a specimen. This problem was approached experimentally, using oriented silicon steel with approximate (110) surfaces, the domain structure of which had been investigated in previous work. The coercivity of monocrystalline disks with different misorientations and heat treatments (thus having different internal stresses and defect densities) was measured. The phase-volumes of the domains oriented at right angles to the preferred direction of the material were determined by magnetostriction measurements on the same crystals. A linear relation was found between the coercivity and the phase-volume of cross domains, but there was no correlation with other parameters. It was concluded that crystal defects, internal stresses, and stray fields (as produced by misorientation) do not influence the coercivity directly but through the cross domains they may cause. Estimates of possible mechanism lead to reasonable results.
Magnetic Anisotropy Induced by Cold Rolling of a 50Ni-50Co Alloy
Authors: Von Neida A. R. , Chin G. Y. , English A. T.
Published: January 2006

An unusual behavior in the magnetic torque curves of cold rolled 50Ni-50Co has been observed. The easy axis of magnetization in the rolling plane was found to switch abruptly from the transverse direction to the rolling direction as reduction increased from 97% to 99%. The torque curves are found to consist of two components, one of which is removed by annealing at 300°C below the recrystallization temperature of the alloy. The component that remains after annealing has a principal easy axis in the transverse direction and is shown to originate from magnetocrystalline anisotropy associated with the {110} 〈335〉 sheet texture. The other component, which is removed by the anneal, is found to be uniaxial with the easy axis in the rolling direction. The magnitude of the uniaxial component is small up to 95% reduction, but increases abruptly thereafter, becoming comparable in magnitude to the contribution from the crystal anisotropy and causing the observed reversal in the principal easy direction after 99% reduction. The uniaxial anisotropy is thought to originate from slip-induced directional order which we have observed in a deformed NiCo single crystal. Since the anisotropy is observed to develop early with deformation in the single crystal, its near absence in ploycrystalline sheet at small reductions is attributed to opposing anisotropy contributions from various texture components. At very large reductions textural changes are observed which can account for the final appearance of the uniaxial component.
Configurational Studies of the Ising and Classical Heisenberg Models
Authors: Domb C.
Published: January 2006

Recent developments in graph classification and enumeration on crystal lattices carried out by the Theoretical Group at King's College are described. As a result of this enumeration, several new terms have been added to the high-temperature specific-heat expansions for the Ising and classical Heisenberg models. The critical behavior is discussed. It has been possible to single out the types of graph which provide a dominant asymptotic contribution to the coefficients of these expansions. Hence the Curie temperature can be related to the statistical properties of self-avoiding walks on crystal lattices.
Convergent, Bounding, Approximation Procedures with Applications to the Ferromagnetic Ising Model
Authors: Baker George A.
Published: January 2006

The Padé approximant method is generalized in such a way that converging upper and lower bounds can be established from the early power series coefficients for a wider class of functions than was previously possible. These procedures are proved to be applicable to many thermodynamic properties of the ferromagnetic Ising model and used thereon. Although nonbounding calculational procedures are shown to be satisfactory for most states of the system, certain pitfalls of those procedures are noted near the critical points.
Fluctuations in Antiferromagnetic Order
Authors: Kociński J. , Wojtczak L.
Published: January 2006

The spatial dependence of magnetic moment of a fluctuation in antiferromagnetic order has been calculated for cubic, two sublattice Heisenberg antiferromagnets with spin s = 12, for temperatures at or above the Néel point without external field. The method of maximal fluctuation has been applied in the two limiting cases of (1) very strong and (2) very weak exchange interaction between the nearest neighbors as compared with that between the next-nearest neighbors. The spatial distribution of magnetic moment and the correlation between spins of a single sublattice have been determined in the Ornstein-Zernike form, and the | sin κ2r | /r form. The qualitative behavior of the parameters κ1 and κ2 which characterize the correlations is the same in both the cases. For the nearest-neighbor number z = 8, at the temperature TN, κ1−1 is infinite, while κ2−1 equals to 0.15 or 0.24 in the units of the lattice constant. At 2TN, κ1−1 is equal to 0.31 or 0.92, while κ2−1 equals 0.11 or 0.22.
Equation of State of a Ferromagnet in the Critical Region
Authors: Domb C.
Published: January 2006

It has been suggested that the equation of state of a ferromagnet in the critical region can be put in the form βmH = (1−t)ΔF[M−1(1−t)Δ−γ](t = Tc/T). F(v) is a function which characterizes the critical behavior, and γ and Δ are two parameters from which all the indices which describe thermodynamic behavior in the critical region can be determined. Griffiths and Helfand have considered possible froms of the function F(v). The present investigation makes use of the higher-order derivatives of magnetization with respect to field as T→Tc+ to provide a series expansion for F(v) in powers of v(t<1); and of corresponding derivatives as T→Tc− to provide information about F(v) near the value corresponding to the spontaneous magnetization (t>1). The forms of F(v) for a number of lattices and models are compared.
Critical-Point Behavior of the Susceptibility of Classical Heisenberg Ferrimagnets
Authors: Freeman S. , Wojtowicz P. J.
Published: January 2006

This paper deals with the critical properties of a class of particularly simple ferrimagnets. We consider the simple cubic and bcc lattices having alternate sites occupied by spins of different magnitudes, SA and SB. Classical Heisenberg exchange interactions are assumed to act between nearest-neighbor sites. For such ferrimagnets, general arguments determine certain features of the dependence of the susceptibility χ and the specific heat on the variables R = SA/SB and j = SASBJ/κT. We are able to show that the critical point occurs at a fixed | j | for either sign of the exchange and arbitrary spin values. Moreover, the exponent γ of the singularity in χ has a value independent of the sign of the exchange and of the spin values. The only exception permitted occurs at the singularity of the simple antiferromagnet (R = 1, j < 0), which has a reduced critical exponent. The nature of the dependence of χ on R permits one to obtain its expansion in powers of j from the known expansion coefficients for the related ferromagnet. A Padé approximant study of χ was carried out for a range of R values. For R ≠ 1, the dominant singularity for positive and negative j showed the familiar power law behavior and was consistent with the general features described above, The critical points and exponents were estimated for the cases studied by a new method making use of the freedom to vary R in the ferrimagnet.
Molecular Field Theory, the Onsager Reaction Field, and the Spherical Model
Authors: Thomas H. , Brout R.
Published: January 2006

We have extended the Onsager method of solution of the many-dipole problem to other types of interaction, particularly to the Ising model, and to the presence of long-range order. We demonstrate that the use of linear response theory for the calculation of reaction field and cavity field is justified on account of the fluctuation theorem. In the paramagnetic phase, the Onsager method reduces to the spherical model. In the magnetized phase, we introduce a scheme of successive approximations and recover the Weiss theory and the modified spherical model after the first and second iterations, respectively.
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.
Magnetic Structure and Metamagnetism of HgCr2S4
Authors: Hastings J. M. , Corliss L. M.
Published: January 2006

HgCr 2 S 4 is a normal cubic spinel whose metamagnetic properties were first reported by Baltzer et al. Our neutron diffraction studies show that the magnetic structure at 4.2°K is a simple spiral, identical with that proposed by Plumier for ZnCr2Se4. The propagation vector τ is parallel to the symmetry axis of the spiral and directed along a particular cube edge in a given domain. The moment of Cr3+ is 2.73 μB, in agreement with the magnetization measurements, and the wavelength of the modulation is ∼42 Å. The wavelength increases with temperature, reaching a value of ∼90 Å at 30°K, and shows very little further variation up to the Néel point (∼60°K). Application of a magnetic field along a cube edge produces no magnetization in that direction, but rather a growth of domains for which τ ‖ H. This process is complete at ∼4 kOe and is followed by a rapid collapse of the spiral into the field direction which saturates at ∼10 kOe. The growth of favorably oriented domains decreases progressively as the direction of the applied field departs from the cube edge.
Magnetic Structure of Cobalt Manganite by Neutron Diffraction
Authors: Boucher B. , Buhl R. , Perrin M.
Published: January 2006

Cobalt manganite CoMn2O4 is prepared at 1250°C and quenched from different temperatures. It always crystallizes in centered tetragonal system but its lattice parameters and inversion degree change by quenching. Measurements of paramagnetic susceptibility above the Curie temperature and magnetization in high fields show the ferrimagnetic behavior of CoMn2O4 with a very weak spontaneous magnetization at 4.2°K. Anisotropy is very strong. The magnetic structure of CoMn2O4 has been worked out from low-temperature neutron-diffraction patterns. In tetrahedral sublattice, spins are collinear, and their mean length is in very good agreement with theory assuming that Co2+ and Mn3+ moments are spin-only ones. In octahedral sublattice, a Yafet-Kittel structure is in very good agreement with experimental results. The B resulting moment is collinear with the A spins along the [110] direction. The net spin value in B sublattice is much smaller than the theoretical one. This low-temperature structure becomes collinear at 70°K.
Reinvestigation of Magnetic Structures of CoCr2O4 and MnCr2O4 Obtained by Neutron Diffraction
Authors: Plumier René
Published: January 2006

Spinels CoCr2O4 and MnCr2O4 display a magnetic structure in which moments on octahedral sites split into two groups. In one of these, transverse components are antiparallel and have the fcc symmetry of the chemical cell. The transverse components of the other group together with those of the tetrahedral sites build a (3a, 3a, a) magnetic cell. Axial components are along [001] for CoCr2O4 and along [110] for MnCr2O4, and are in good agreement with magnetization measurements. Good agreement is also obtained between measured and calculated magnetic intensities. These structures can be explained in a molecular-field approximation. Short-range order is still present at low temperatures.
Indirect Exchange Interaction in Metals—A Status Report
Authors: Kittel C.
Published: January 2006

A survey is given of the indirect coupling of nuclear magnetic moments in metals via the hyperfine interaction with conduction electrons. The treatment is given in terms of the wavevector-dependent static susceptibility of the conduction electrons. The criterion for the absence of a long-range uniform magnetization is discussed. The usual divergence in the self-energy of a single nuclear magnetic moment in a metal is shown to be caused by the attribution of a zero range to the contact interaction, whereas the appropriate range is ħ/mc. The divergence recently claimed in the interaction between two nuclear moments at absolute zero is believed to be a manifestation of the Kondo effect. Mean free path and correlation effects are considered.
Effect of Virtual Spin Waves on the Properties of Strongly Paramagnetic Metals
Authors: Schrieffer J. R.
Published: January 2006

The theory of spin fluctuations in nearly ferromagnetic metals is presented and their effect on the properties of such systems is discussed. The importance of momentum-dependent exchange and band-structure effects is stressed.
Effect of Magnetic-Ions Multiplicity on Exchange Interaction in Crystals
Authors: Vonsovsky S. V. , Svirsky M. S.
Published: January 2006

The theory of s-d(f) direct and indirect exchange coupling in crystals involving the ions of d and f metals is generalized by taking into account variation of multiplicity of magnetoactive shells of these ions. The generalized exchange Hamiltonian are applied to the problems of electro- and superconductivity and those of magnetic order in metal crystals containing the magnetic ions. The excitations of ion multiplicity is shown to lead to the minimum of electroresistance at the temperature which exceeds the multiplicity excitation energy. The conditions are set at which the following decreasing of temperature results in appearance of the electroresistance maximum. It is shown that virtual multiplicity excitations of magnetic ions induce the repulsion of singlet pairs and thus prevent from the establishment of superconductivity at such electron coupling. Due to this effect the critical temperature of La decreases when Eu impurities are added. For triplet pairs the above-mentioned interaction can have the attraction nature. This ensures the real possibility of the nonphonon mechanism of superconductivity in three-dimensional crystals with high critical temperature of superconductivity. The effect of changes of multiplicity on appearance and character of long-range magnetic order in crystals with localized magnetic ions is considered.