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Open-Shell Hartree—Fock Molecular Orbital Theory of Transition Metal Ion Complexes: KNiF3
Authors: Ellis D. E. , Freeman A. J. , Ros P.
Published: January 2005

In order to investigate the magnetic properties of transition metal salts, we have developed the open shell single determinant Hartree—Fock SCF molecular orbital method for transition metal ion complexes. This cluster approach removes many of the shortcomings of earlier treatments1 and, in principle, provides a framework for obtaining fairly accurate and meaningful results within the single determinant approximation. These wave functions thus provide a realistic basis set for configuration interaction calculations of superexchange and other properties. By choosing a special one-center basis set for the cluster, we are able to compute all matrix elements of the molecular Hamiltonian accurately including the effects of the crystal field external to the cluster. Furthermore, the computation is sufficiently fast so that we may include all electrons of the molecular cluster while allowing considerable variational freedom in all representations.

Detailed self-consistent field calculations have been made using, as example, KNiF3, the antiferromagnetic Perovskite treated extensively by previous workers.1 By considering a NiF64− cluster in its crystalline environment, the crystal field splitting parameter 10 Dq is found to be in fairly good agreement with experiment, but sensitive to a number of factors. The resulting molecular orbitals are compared with those obtained by earlier LCAO calculations. While the radial distributions are quite reasonable, the limitations imposed on these first calculations with this one-center method are apparent; the restriction to low angular momentum in the basis sets used leads to a poor description of ligand core orbitals.

Spin densities throughout the cluster have been computed; neutron magnetic form factors have been calculated for comparison with experiment. In agreement with earlier work2 based on a single parameter LCAO scheme, we find that the cluster spin density gives a large peak in the form factor near zero scattering angles compared with the Ni2+ free ion result. This peak is seen to arise from the eg spin density on the ligand sites; the spin density from all the remaining molecular orbitals, unpaired by exchange polarization, is found to be small (≈2%).

The limitations imposed by the restricted basis set used have led us to consider a triatomic system, Ni2F, as the cluster for the calculation of F19 hyperfine interactions. While the calculated isotropic hyperfine term was found to be too large relative to experiment, the computed anisotropic hyperfine interaction agreed (surprisingly) well.

A full report will be submitted to the Physical Review.
Spontaneous Band Magnetism
Authors: Goodenough John B.
Published: January 2005

With sharply defined, critical overlap integrals Δc and Δcf for a localized-electron ⇆ collective-electron transition and for spontaneous band ferromagnetism, the conditions for band ferromagnetism to occur are: Δc <Δb <Δcf, and Δc <Δab <Δcf <Δb, where the overlap integrals Δab <Δb are each proportional to the bandwidths of antibonding and bonding bands, respectively. Spontaneous magnetism also depends upon the electron/atom ratio: Half-filled bands may exhibit antiferromagnetism, but not ferromagnetism. If Δc <Δb <Δcf, bands less than one-quarter filled may exhibit ferromagnetism with magnetization ≤ ndμB per atom and a distributed spin density as in ZrZn2, where nd, nh, and nab are numbers of electrons, holes, and antibonding electrons per atom. Bands more than three-quarters filled may be ferromagnetic with a localized atomic moment of nhμB. Bands more than half-filled and less than three-quarters filled give a localized atomic moment of nhμB, if Δc <Δb <Δcf, and are either ferromagnetic or exhibit a spiral-spin configuration. However, if Δc <Δab <Δcf <Δb, ferromagnetism with a reduced atomic moment of nabμB per atom is predicted. The spin density is localized, but a small negative-spin density may occur at large distances from the atom. It is indicated how these ideas can account satisfactorily for the spontaneous magnetism, atomic moments, and spin-density distributions in first-row transition metals.
Application of Cluster Expansions to the Dynamics of the Heisenberg Ferromagnet
Authors: Reiter G. F.
Published: January 2005

We describe an approximate method for treating the dynamics of the Heisenberg ferromagnet, based upon a cluster expansion of the nonequilibrium density matrix. The dynamical variables are taken to be the magnetization and the spin—spin correlation function. The equations of motion for these quantities yields a hierarchy of equations, involving higher order correlation functions, similar to the BBGKY hierarchy for a classical gas. These are terminated by neglecting correlation functions between spins on three different sites. In the spin-wave region it is shown that this procedure leads to the correct temperature dependent spin-wave frequency renormalization. When applied to the longitudinal fluctuation in the magnetization, the resultant equations may be interpreted as equations of motion for the distribution of magnons in phase space (the Wigner distribution). A dispersion relation for the magnon density fluctuation is derived, which yields a spectrum of quasiparticles and describes the effect of the interaction between magnons on the propagation of local density fluctuations.
Spin Waves in a Two-Band Ferromagnetic Metal
Authors: Antonoff Marvin M.
Published: January 2005

The theory of ferromagnetism in itinerant electron systems has been developed in recent years as a possible explanation for the properties of the 3-d metals. In the work on the spin-wave states, excited states involving an electron in one band and a hole in another have been neglected. However, band-structure calculations indicate that the Fermi level intersects several d bands, often near degeneracies. In these latter regions of the Brillouin zone the interband scattering of electrons will distort the band structure, and will introduce interband electron—hole pairs into the acoustic spin wave eigenfunctions, thereby affecting the spin wave spectrum. To the present time, interband scattering has been neglected in spin-wave investigations, representing a weakness of the theory. The interband effects might be expected to be important in such metals as Ni and Ni alloys, where the Fermi energy lies close to degenerate band structure. We consider a metal consisting of two bands with a ferromagnetic ground state. The electrons are assumed to interact via the Coulomb potential. Interband scattering of electrons by the other electrons in the system couples states of the same wavevector k and like spin σ. The interaction itself is spin-dependent since the interband scattering includes an exchange contribution. The modification of the spectra of the single-particle excitations and the collective modes by the interband transition is discussed.
Note on Spin-Wave Operators
Authors: Roth Laura M.
Published: January 2005

If, together with the spin lowering operator S−, which creates a spin deviation, we consider the operator Ŝ+ = Q−s (S+Sz)−1 S+, where Q−s excludes the Sz = − S state, we can show that the number of spin deviations S − Sz = S−Ŝ+, and the operators obey the commutation relations [Ŝ+, S−] = 1 − (2S+1) P−s, where P−s is the projection operator for the − S state. The Heisenberg spin Hamiltonian written in terms of these operators assumes the Dyson form. We compare the Ŝ+, S− operators with ideal spin wave operators, and also use them to obtain the random-phase approximation results in a simple and revealing form.
Simple Narrow-Band Model of Ferromagnetism due to Intra-Atomic Exchange
Authors: Roth Laura M.
Published: January 2005

We consider a narrow band constructed from two degenerate orbital states such as dz2 states. Including intra-atomic Coulomb and exchange integrals as well as hopping on a bcc or sc lattice, we find that if n is the number of electrons per atom, for n = 1, the tendency is, for sufficiently narrow bands, for the crystal to break up into two sublattices A and B, with primarily orbital 1 on sublattice A and primarily orbital 2 on sublattice B, and for the spins to line up ferromagnetically. A self-consistent method is used to extend the result beyond the narrow band limit, and the stability of the ferromagnetic state is investigated by calculating the spin wave spectrum as a collective mode. The effect of intra-atomic exchange and orbital degeneracy on the effective exchange parameter is discussed for n≤1.
Exchange Energy, Stress, and Momentum in a Rigid Ferrimagnet
Authors: Morgenthaler Frederic R.
Published: January 2005

A self-consistent formulation of the exchange energy density, effective exchange field, and Poynting vector is carried out, for a general ferrimagnet, in terms of the spin and orbital angular momentum densities. When there is more than one magnetic lattice or when the gyromagnetic ratios are tensor quantities, this formulation leads to an exchange energy density and Poynting vector that differ from those commonly employed. The associated boundary conditions at a surface of passive discontinuity are also discussed; power flow considerations lead to the conclusion that one of these is a dynamic boundary condition.

With the help of the correspondence principle and a quasi particle interpretation of spin waves, a small-signal energy density, momentum density, and stress tensor are postulated for a ferromagnet. The associated small-signal force density (postulated to equal the divergence of the stress tensor minus the time rate of change of the momentum density) is found to be the negative of the force density that accelerates the envelope of the spin wave packet and is interpreted as a reaction force density acting upon the lattice. A prediction is made that a magnon incident upon a surface of discontinuity such as a material—air interface, will exert an exchange-radiation pressure on it.
``Super'' Transferred Hyperfine Interactions for Fe3+ Salts
Authors: Šimánek E. , Li Huang Nai , Orbach R.
Published: January 2005

The experiments of Treves on rare-earth orthoferrites exhibit a hyperfine field at 57Fe which decreases on going from LaFeO3 through LuFeO3. In this paper we calculate the increase of hyperfine field at 57Fe on going from Fe3+ in dilute oxide to LaFeO3, and find for the overlap part an increase by 51 kG which is about twice as large as the experimental value. We suggest that the overlaps between ligands and inner shells of the magnetic ion are reduced due to a repulsion of closed shells. The observed change of hyperfine field with rare-earth substitution is qualitatively explained by applying the Slater model of superexchange to the mechanism of ``super'' transferred hyperfine interaction.
Is 3.25% Si Oriented Core Steel The Ultimate?
Authors: Getting Milan P.
Published: January 2005

Significant developments in core steel are reviewed briefly. The role of magnetic and physical properties of 3.25% Si oriented steel are discussed in some detail as they enter into the construction of cores for distribution and power transformers. The magnitude of the strain sensitivity and/or flatness of strip in practical core structures is examined in some detail. An alternative is suggested, some of the anticipated difficulties are discussed, and an estimate is made of anticipated improvement in material properties.
The Solubility of Sulfur in Silicon Iron
Authors: Grenoble H. E.
Published: January 2005

An earlier determination of the solubility of sulfur in silicon iron by Ainslie and Seybolt appears to be somewhat high for a material prepared in the manner of cold-rolled oriented steel strip. Accordingly, a redetermination has been made with materials having this particular processing.

The solubility was obtained using an equilibration method with the reference potential of sulfur provided by powdered ferrous sulfide or by a high-sulfur silicon iron. For the primary recrystallized structure the solubility is found to be 0.015% at 900°C and increases to 0.025% at 1100°C. For a large-grain structure the solubility at 900°C is significantly lower, indicating that there is a grain size effect upon solubility. This effect diminishes with increasing temperature.
Coalescence of Sulfides during Secondary Growth in 3% Silicon—Iron
Authors: Flowers J. W. , Karas S. P.
Published: January 2005

The behavior of manganese sulfide inclusions in the development of the cube-on-edge texture in 3% silicon—iron was investigated. Primary-recrystallized specimens of two commercial alloys were heated from 590°C to 760°, 870°, 980°, 1090°, and 1200°C in dry hydrogen. The sulfide-particle sizes were measured as a function of annealing temperature by electron microscopy. The measurements showed that a marked coalescence of the particles occurred between 870° and 980°C. In one of the alloys studied, vigorous secondary grain growth took place concurrently with the coalescence of the inclusions. The secondary growth was complete before any sulfur was removed from the specimens by diffusion. In the second alloy, which had a weaker cube-on-edge component in the primary recrystallization texture, normal grain growth occurred despite a similar coalescence of the sulfide particles.
Development and Application of Low-Noise 6.5% Si–Fe Sheet
Authors: Kernick A. , Lane D. H. , Ogden J. W. , Pavlovic D. M.
Published: January 2005

The effects of composition, magnetic annealing and texture on the magnetic properties, magnetostriction, and core noise of pilot-produced 6.5% Si–Fe sheet and transformer cores have been studied and the results compared with the core-loss and core-noise characteristics of domain-oriented 2V-CoFe and cube-textured 3% Si–Fe transformer cores. The application of magnetic annealing reduced magnetostriction of 6.5% Si–Fe sheet to 1×10−6 at 18 kG. The use of a low-magnetostriction core material, such as 6.5% Si–Fe, was shown to result in a considerable reduction in transformer core noise, reducing in turn the maximum noise level of a 3-phase, 400-Hz, 1250-VA static inverter to 50 dB in an acoustic frequency range of 0.4–20 kHz.
Domain-Wall Motion in Grain-Oriented Silicon Steel in Cyclic Magnetic Fields
Authors: Houze G. L.
Published: January 2005

A technique has been developed for the direct observation of magnetic domain-wall motion in grain-oriented silicon steel. The magneto-optical Kerr effect was employed to obtain a visible contrast between antiparallel domains. Domain-wall motion at 30, 60, and 120 cps was photographed using a high-speed camera synchronized with a high-intensity electronic-flash system. Motion pictures at rates up to 5500 frames/sec were obtained. The effects of peak induction, waveform and frequency on domain-wall motion were observed. The films showed that domain-wall positions did not repeat precisely from cycle to cycle, particularly at high inductions, and that the average domain-wall spacing decreased with increasing frequency. Frame-by-frame analyses of these high-speed films revealed that domain walls may hang up, or become pinned several times during a reversal, and that a domain wall does not necessarily move as an entity. The pinning effects are attributed to the presence of non-magnetic inclusions and/or surface defects. The possible effects of pinning on core losses are discussed, and it is concluded that pinning could be responsible for a substantial portion of the anomalous losses.
Texture—Electrical-Property Correlations in Oriented Silicon Steel
Authors: McCarty M. , Houze G. L. , Malagari F. A.
Published: January 2005

Grain-by-grain measurements of crystallographic orientations have been made to study the relationship between texture and electrical properties of oriented silicon steel. An etch was used to produce a faceted surface of (100), cube, planes thus making each grain brightly reflective in three perpendicular directions. An optical goniometer was used to determine the crystallographic orientation of each grain. Orientation is defined in terms of three angles as follows: (1) α-the divergence in the plane of the sheet of the [001] direction from the rolling direction, (2) β-vertical tilt of the [001] direction from the rolling direction, (3) γ-the rotation of the (110) plane about the direction of magnetization. Statistical methods were used to calculate the degree of texture in terms of the spread or distribution of these angles and to correlate the distribution with electrical properties. A strong correlation was found between α and permeability at 10 H. About 75% of the variation in permeability at 10 H could be accounted for through variations in α. Only about 55% of the variation in core loss could be accounted for through variations in α. Correlation of β with permeability was not significant. The angle γ should not appreciably affect electrical properties and no correlation was found.
A Comparison of the Use of Aluminum and Vanadium Nitrides for Making Grain-Oriented Silicon—Iron
Authors: Fiedler H. C.
Published: January 2005

The cube-on-edge secondary recrystallization texture is developed in silicon—iron strip containing either aluminum- or vanadium-nitride particles. For minimum losses, the constituents comprising the particles must be capable of being removed from or dissolved in the alloy. Although the nitrogen is readily removed by a heat treatment in dry hydrogen, aluminum oxide is formed at and beneath the surface of the strip, with the result that for the same degree of grain orientation, the losses are higher in alloys containing aluminum than in alloys containing vanadium.
Effect of Sulfur on the High-Density Magnetic Properties of Oriented 3¼% Silicon Steel
Authors: Benford James G.
Published: January 2005

Although it is generally accepted that sulfur remaining in oriented silicon steel after final treatment has a harmful effect on the magnetic properties, the effects have not been determined quantitatively. It was the object of the present investigation to determine quantitatively those effects. Core loss is decreased in the range 0.018% to 0.004% sulfur by 0.002 W/lb/15 kG/60 for each thousandth of a percent of sulfur removed. At 17 and 18 kG, the losses in the range of 0.018% to 0.008% sulfur are reduced by 0.005 and 0.006 W/lb/60, respectively; and by 0.012 and 0.016 W/lb/60, respectively, in the range 0.008% to 0.004% sulfur for each thousandth of a percent of sulfur removed. Permeability is increased in the range 0.018% to 0.004% sulfur by 400, 105, 25, and 1 for 15, 17, and 18 kG and 10 Oe, respectively, for each thousandth of a percent of sulfur removed. It is theorized that the breaks in the core loss curves for 17 and 18 kG at 0.008% sulfur are related to sulfur removal in a heterogeneous diffusion system in which a surface zone of the steel becomes virtually free of domain-blocking sulfides at about 0.008% sulfur. When this zone reaches a depth comparable to the width of domains, a change in the slope of the curve results.
Domain Configuration and Losses in Cube-Textured Silicon Iron
Authors: Wiener G. W. , Foster K. , Shull D. S.
Published: January 2005

Studies of the domain configuration of single crystals with the (001) plane parallel to the surface in 3% silicon iron were made at various states of magnetization up to saturation. These measurements were made in the 〈100〉 and 〈110〉 direction. It was found in both cases that the predominant magnetization process was 90° wall motion and nucleation of new 90° wall domains. Alternating current losses and dc hysteresis losses were measured on highly oriented polycrystalline silicon iron having the (001) [100] orientation in a direction parallel to the 〈100〉 and parallel to the 〈110〉 direction. A large increase in losses was noted in going from the 〈100〉 to the 〈110〉 direction. Only a small part of the increase was due to an increase in the hysteresis loss. It is concluded that the large increment in total losses in the 〈110〉 direction is related to the nucleation of a unique 90° domain-wall structure. The data obtained also suggest that the easiest process of magnetization is not necessarily the motion of 180° walls.
Three-Sublattice Ferrimagnetic Structure
Authors: Boucher B. Y. , Buhl R. , Perrin M.
Published: January 2005

We show that, in the hypothesis of molecular field theory, a ``star'' structure (one direction for each sublattice moment) can exist and be stable. Such a structure becomes collinear for some T1<Tc. From the variation of the magnetization of one sublattice vs temperature in the neighbourhood of T=T1, we deduce the high-temperature structure. The neutron diffraction measurements relative to (MnxNi1−x) (NixMn2−x) O4 (0.74<x<0.93) show the existence of a ``star'' structure which explains the spontaneous magnetization values.
High-Field Magnetization Curve of Porous Polycrystalline YIG
Authors: Schlömann Ernst , Kohane Theodore
Published: January 2005

The magnetization has been measured as a function of magnetic field strength on porous polycrystalline YIG (porosities up to 27.1%). Measurements on spherical samples were done with a vibrating sample magnetometer at internal fields between 30 Oe and 9 kOe, on toroidal samples at fields up to 50 Oe. The results agree with an extension of Néel's theory, not only at high field strength but down to the remanence point. In the extended theory the influence of the exchange interaction has been taken into account. This refinement of the theory is essential for obtaining agreement with the experimental data at relatively low magnetic fields (below 50 Oe), but of little consequence at higher fields. From a comparison of the experimental data with the theory, we infer the mean-squares deviation of the local saturation magnetization from its average. The values obtained agree well with values deduced from measurements of the longitudinal susceptibility at microwave frequencies. The analysis of the data also indicates that the materials investigated contain inclusions of a secondary magnetic phase (approximately 1% magnetite) in addition to pores.
Chemical Vapor Growth of Single-Crystal Magnetic Oxide Films
Authors: Pulliam G. R.
Published: January 2005

The chemical vapor deposition technique provides a means of growing single-crystal films of ferrite and garnet magnetic oxides on nonmagnetic substrates. The technique involves a chemical reaction at elevated temperatures between volatile metallic compounds and gaseous oxidizing agents on the substrate surface to form the solid film. It is possible to control the orientation of the magnetic vector with respect to the film, the film composition, and the surface condition of the film. The factors which affect the achievement of epitaxy and the crystal quality of the film include the structural similarity between the substrate crystal and the film, the chemical conditions of the reaction, the deposition temperature, the rate of crystal growth, and the relative expansion characteristics of the film and substrate. Epitaxial deposits of a variety of ferrites have been made on MgO, Al2O3, and MgAl2O3 single-crystal substrates in the deposition temperature range of 800° to 1100°C. Film thicknesses in the range 0.5 to 500 μ have been produced in (100), (110), and (111) orientations. The values obtained for saturation magnetization anisotropy constant and resonant linewidths are similar to bulk-crystal values of the same composition.
Growth, Magnetic, and Microwave Characteristics of Monocrystalline BiCaVIG
Authors: Hodges L. R. , Wilson W. R. , Rodrigue G. P. , Harrison G. R.
Published: January 2005

Monocrystalline ferrimagnetic pentavalent vanadium garnets conforming to the general formula {Bi3−2yCa2y} [Fe2] (Fe3−yVy)012 for 1.0<y≤1.4 have been grown and their magnetic and microwave properties evaluated. A molten flux technique using PbO–Bi2O3 flux was used in the growth procedure. The PbO/Bi2O3 ratio (mole percent ratio) in the single-crystal melt from 0 to 4 covers the compositional variation listed above. Single crystals have been produced with 4πMs values from approximately 0 to 630 G. The minimum linewidth has been measured for the composition y=1.3 to be approximately 1 Oe at 5 GHz (0.7 Oe at 1 GHz). Heat treatment of the finished spheres has been observed to improve the linewidth as in YIG compounds. Data on linewidth, anisotropy field, and 4πMs, as functions of composition, are presented.
Hall Effect in Single-Crystal Lithium Ferrite
Authors: Wang Franklin F. Y. , Gravel Robert L. , Kestigian Michael
Published: January 2005

Between 170° and 330°K, the Hall mobility of the flux-grown lithium ferrite single crystal has a maximum at 295.5°K. At 295.5°K, the ordinary Hall coefficient R0 was found to be +3.26×102 cm3/C, which corresponds to a carrier concentration of 1.92×1016-cm−3. The extraordinary Hall coefficient R1′ was 1.9×102 cm3/C. Above 295.5°K, μH = 1.39×10−2[exp(1.54×103/T) −1], which indicates a mechanism of optical mode scattering. Below 295.5°K, μH = (2.591×105/T) exp(−0.149 eV/KT), which indicates a diffusion mechanism. The majority carriers (p-type) can be attributed to the Fe2+ ions, and the minority carriers (n-type) to the oxygen vacancies.
Variation of the Low-Temperature Resistivity in Dilute Magnetic Alloys
Authors: Klein Michael W. , Harrison Ralph J.
Published: January 2005

We examine the effect of internal fields upon resistivity of dilute magnetic impurities in nonmagnetic metals, using the second Born approximation. Several distributions of internal fields are considered. We find that the internal field effects suppress the Kondo log T term at moderately low temperatures (several orders of magnitude above the Suhl—Abrikosov resonance temperature Tr). This low-temperature behavior is found to be sensitive to the variation of the probability distribution of the fields P (H) near zero field. When P (H) is proportional to Hn−1 for small H, the change in the low-temperature resistivity Δρ (T) is found to be proportional to Tn (1-α logT). α is about 0.06 for copper and gold alloys. More generally, we find that, except for the small logT term, Δρ(T) is proportional to that part of the low-temperature specific heat which arises from the magnetic disordering of the impurities. For an Ising model, n=1, and the resistivity is thus approximately linear in T for 0.01<T<1°K. This linearity has been observed for a 0.1% Au-Fe alloy where the resistivity has been measured to sufficiently low temperatures, thus giving additional support to the Ising-like internal field model of the specific heat and Δρ(T). The theory predicts the resistivity maximum as well as the disappearance of the minimum as a function of the impurity concentration in reasonable agreement with experiment. It is suggested that the low-temperature resistivity measurements be used to probe the distribution of the internal fields in the dilute alloy system.
Hyperfine Fields in Fe-Si Alloys
Authors: Budnick J. I. , Skalski S. , Burch T. J. , Wernick J. H.
Published: January 2005

We have measured the hyperfine field at Fe and Si nuclei in Fe-Si alloys containing 18.4 to 26.5 at. % Si by the NMR spin-echo technique at 4.2°K. We observe Fe resonances from nuclei at sites with 3, 4, 5, 6, and 8 Fe nearest neighbors at frequencies which are in good agreement with the reported Mössbauer results. In Fe3Si, we observe an additional line at about 31.5 Mc/sec which we identify with the Si nuclei. In the 23.0 at. % sample, this line is diminished in intensity and another line appears at about 47 Mc/sec which grows in intensity as the Si concentration is decreased below 23.0 at. %. At 22.3 at. % Si and below, the 31.5-Mc/sec Si line is not observed. In addition, our data shows that a significant change in the Fe hyperfine field at sites with 4 and 8 nearest-neighbor Fe atoms occurs between 22 and 24 at. % Si. These observations on the hyperfine fields correlate well with the anomalous behavior of the resistivity in this concentration range and indicate a change in the electronic structure of Fe-Si alloys that occurs in the vicinity of 23 at. % Si.
Pulsed NMR in Fe
Authors: Stearns Mary Beth
Published: January 2005

Measurements were made of the free induction decay (FID) and spin echo amplitudes of 57Fe in pure Fe and some of its alloys. Complex spectra are observed consisting of many oscillations often covering a range of many Mc/sec. The spectral shape is very dependent on the pulse length, τ, and applied rf field, H1. Some of the gross features of these spectra can be explained in terms of turning angle effects due to being off resonance and having a large enhanced rf field at the nucleus. However, there are other prominent features of the spectra that are not consistent with and not explained by the usual picture of NMR in ferromagnetic metals. One most puzzling feature is that in terms of an enhancement factor, ε, the spectra appear as if ε were about a factor 2.5 times larger on the high as compared to the low frequency side of resonance. These features have also been seen in the spin-echo spectra of Fe alloys. Since the shape of the spectra is dependent on the rf power and τ and contains a large asymmetry, it appears very doubtful that at present Fe-alloy spectra can be reliably unfolded to obtain the variation of the internal field for second- or higher-neighbor impurity atoms.
The Kondo Effect—The Link Between Magnetic and Nonmagnetic Impurities in Metals?
Authors: Schrieffer J. R.
Published: January 2005

Kondo has shown that the resistance minimum in dilute alloys which exhibit localized magnetic moments arises from a resonant antiferromagnetic (J<0) exchange scattering. Below the Kondo temperature Tk = T0 exp − [1/N(0) | J |], the conventional spin-disorder scattering is dominated by this resonant scattering. Here T0 is of order the Fermi temperature, and N(0) is thedensity of states at the Fermi surface. Perturbation calculations of the susceptibility in powers of N(0) | J | valid for T>Tk show that this exchange scattering acts to reduce the magnitude of the localized moment by inducing a localized polarization of the conduction electrons which partially compensates the impurity moment. More complete analysis indicates that the susceptibility, which for T≫Tk has a Curie-law term, saturates at a finite value for T≪Tk. This suggests that at least some of the alloy systems which are traditionally viewed as nonmagnetic in the context of the Friedel-Anderson type of Hartree-Fock analysis, are best described in terms of Kondo compensated magnetic impurities. To check this view, the properties of an exchange model with a realistic exchange integral are being worked out. One finds that the resistivity of the (nonmagnetic) Al based 3-d metal alloys is largest at the center of the 3-d series, dropping on either side, in agreement with experiment. Since these experiments are conventionally quoted as evidence for the validity of the Hartree-Fock treatment, further comparisons with experiment are necessary to resolve the question. Other results of the analysis and experimental evidence for the temperature dependent spin compensation are discussed.
NMR and Magnetic Susceptibility of Co Magnetic Impurities in Transition Metal Hosts
Authors: Brog K. C. , Jones Wm. H. , Booth J. G.
Published: January 2005

The 59Co NMR has been observed in Mo-y at. % Co and W-x at. % Co alloys where: y=0.54 and 1.08; x=0.53 and 1.05. The NMR frequency shifts exhibit a strong temperature dependence which can be correlated with the temperature dependent part of the bulk susceptibility. The resonance lineshapes are symmetrical and the linewidths show a temperature and field dependence which is approximately linear in H/T. The magnetic susceptibilities can be fitted to an equation of the Curie-Weiss form: χ−χ0=C/(T−θ) with θ∼−11°K and −24°K for the W and Mo hosts, respectively. In each alloy the temperature-independent susceptibility is approximately equal to that of the host metal, and the values of the Curie constant correspond to ``effective'' moments per Co atom (gS) of 1.79±0.10 in W and 1.52±0.15 in Mo. Using temperature as an implicit parameter over the range of 4.2°–300°K, a plot of the Knight shift vs susceptibility for each alloy yields a linear relationship from which the hyperfine field per Bohr magneton is found to be much smaller than expected for Co. Assuming pure d states this suggests that the ``effective moment'' in these alloys does not reside entirely on the Co atom, and the host matrix is polarized in the vicinity of the impurity; however an alternate explanation is that positive contributions to the internal field such as an admixture of s character into the d states of the impurity tend to cancel the large negative hyperfine field due to core polarization by the unpaired d spins.
Hyperfine Interactions at 57Fe Nuclei in Intermetallic Compounds of the Fe–Mn System with the β-Manganese Structure
Authors: Kimball C. W. , Tison J. K. , Nevitt M. V.
Published: January 2005

Mössbauer spectroscopy has been used to investigate intermetallic compounds of the Fe–Mn system with the β-Mn structure. The data are analyzed using a model based on recent NMR results of Drain. Although β-Mn is nonmagnetic, alloy phases containing 10 at. % or more of Fe are magnetically ordered at 4.2°K. Iron is found to preferentially occupy Site II. The slight dependence of the isomer shift and quadrupolar coupling on Fe concentration is indicative of the electronic similarity of Fe and Mn in a given site. The average Debye temperature for Fe in β-Mn is ∼100° larger than that for Fe in α-Mn.
Low-Temperature Resistivity and the Sign of the Exchange Integral
Authors: Sarachik M. P. , Shaltiel D.
Published: January 2005

Kondo has predicted that a minimum should occur in the resistivity of alloys which exhibit a localized moment if they have a negative s-d exchange integral, and a logarithmic decrease in resistivity with decreasing temperature should take place for alloys with positive exchange. The exchange J is known from EPR measurements to be negative for gadolinium in palladium and positive for manganese in palladium. Measurements of resistivity as a function of temperature for several dilute alloys of Pd-Gd show no such minima, and no change in resistivity at the Curie point. The Pd-Mn alloys show a sudden linear decrease in resistivity below a temperature which varies with manganese concentration and which corresponds approximately to the magnetic transition temperature of the alloy.
Occurrence of a Minimum in the Electrical Resistivity of Chromium Alloys at Low Temperature
Authors: Arajs Sigurds , Dunmyre G. R.
Published: January 2005

Electrical resistivity as a function of temperature between 4.2 and 70.0°K has been determined for binary chromium alloys containing 0.4, 0.8, 1.7, and 2.6 at. % nickel, 0.4, 1.2, 1.7, 4.4, 6.2, and 8.0 at. % cobalt, and 2.1 and 4.0 at. % manganese. The chromium-cobalt alloys with 4.4, 6.2, and 8.0 at. % cobalt exhibit a minimum in the resistivity vs temperature plot at low temperatures. A similar minimum occurs also for 0.4 and 0.8 at. % nickel-chromium alloys, but not in any of the chromium-manganese samples.
Temperature Dependence of the Sm3+ Spin 〈 S(T) 〉 in Intermetallic Compounds
Authors: Jones E. D. , Hesse J. E.
Published: January 2005

The temperature dependence of the Sm3+ spin 〈 S(T) 〉 in the NaCl cubic intermetallic compounds SmP, SmAs, SmSb and SmBi has been studied by the observation of the nuclear magnetic resonance (NMR) of the nonmagnetic constituent, e.g., 31P:SmP etc. The Knight shifts in these intermetallic compounds were found to consist of two principal contributions: (1) a temperature-independent term K0 equal to the Knight shifts in the nonmagnetic isomorphs, e.g., 31P:LaP etc., and (2) a temperature-dependent term, proportional to the Sm3+ spin 〈 S(T) 〉. In all the compounds, the temperature-dependent part of the Knight shift reversed sign at T≃300°K in agreement with theory. The temperature-dependence of the Sm3+ spin 〈 S(T) 〉 was calculated for a Sm3+ ion in an octahedral cubic field and an exchange energy of the form 2βHexS. The 31P Knight shift in SmP was measured between 4.0 and 575°K with the result that good agreement between theory and experiment was obtained using: (1) a crystal-field splitting of 130°K between an upper quartet and lower doublet of the J=52 ground state and (2) an exchange field Hex=λS of strength λβ/k=1.5°K.
Magnetic Materials for Space Power Systems
Authors: Beiler A. C.
Published: January 2005

Deep space missions will require megawatts of electric power. Nuclear-electric systems, reliable for 50 000 h, will need materials to operate up to 1600°F in vacuum. They must withstand liquid alkali metals or their vapors and nuclear or cosmic radiation. Magnetic materials must meet high electrical efficiency requirements under severe environmental conditions and in some cases, stringent mechanical requirements.

Many types of electrical equipment, e.g., inverters and other devices in the manned quarters, will not be required to withstand such severe environments, but must still operate with the highest efficiency and reliability. Materials for such uses and the basis of their selection are reviewed.

The components and their environmental and operating requirements are reviewed. The status of available magnetic materials and the basis of their selection to satisfy these requirements for the two principal temperature ranges, 800°–1100°F and 1100°–1600°F, are presented. Weak areas and gaps are identified. The major gap is in materials for high-speed rotors in the highest temperature range.

The various metallurgical approaches applied to this problem and the necessary magnetic and physical compromises are presented.

The three approaches now being investigated are: (1) improved martenistic alloys; (2) improved precipitation strengthened Co alloys; (3) new dispersion strengthened Co and Fe-Co alloys. Encouraging preliminary results are presented.
Electron-Metallographic Examination of Soft-Magnetic Nickel—Iron Alloys
Authors: Ananthanarayanan N. I. , Coles J. A. , Slepian R. M.
Published: January 2005

Etching and replication techniques, suited for electron metallography of grain-oriented 50Ni-50Fe alloy tapes, are described. Using these techniques, the electron microstructures of several such tape materials have been compared in relation to their metallurgical history, secondary recrystallization behavior during annealing, and as-annealed magnetic hysteresis-loop characteristics. The existence of relatively large variations between materials in regard to the dispersions in their microstructures has been established. A correlation is shown, indicating that materials with rectangular hysteresis loops are invariably those having fine dispersions in the microstructure visible in the electron microscope. The dispersion control essential to the manufacture of grain-oriented nickel—iron alloy materials has been achieved from the results of this work.
Effects of Composition and Cooling Rate on the Initial Permeability of Mumetal
Authors: Snee D. J.
Published: January 2005

This paper shows the effects of Ni and Cr content and cooling rate on the initial permeability of Mumetal. Several laboratory heats having a range of composition from 74% to 77% Ni, 1% to 3% Cr, and 5% Cu were vacuum melted and hot and cold rolled to a thickness of 0.014 in. After annealing in dry hydrogen at 2150°F for 4 h, the samples were cooled at rates from 50° to 2000°F/h below 1200°F. Magnetic test results show that initial permeabilities (actually μ at 40 G) of over 50 000 can be obtained provided the proper Ni–Cr combination is used with the optimum cooling rate. The best results were obtained for a 200°F/h cooling rate for alloys having a Ni content from 75.5% to 76.5% and Cr from 2.0% to 2.9%. For a given Ni content, the cooling rate for the highest initial permeability generally increases with decreasing Cr content. For constant Cr content, the optimum cooling rate increases with increased Ni. An empirical equation relating Ni and Cr content and cooling rate to permeability is given.
Production and Properties of Grain-Oriented Commercially Pure Iron
Authors: Kohler D. M.
Published: January 2005

Flat-rolled commercially pure iron such as Armco magnetic ingot iron has been found useful in applications requiring high-flux density. The existing commercial iron products do not have a strong texture. The development of a process for grain orientation in commercially pure iron could be expected to substantially improve the magnetic properties, making possible new applications.

In order to obtain a strong secondary recrystallization texture of the cube-on-edge type it is necessary to restrain grain growth of the primary structure, so that this fine-grained structure is maintained until secondary growth occurs at higher temperatures. Inhibitors added to the melt have not been effective in inhibiting the strong normal grain growth in commercially pure iron.

Effective inhibition of normal grain growth has been accomplished by diffusing extra sulfide inhibitors into the primary grain boundary in a very early stage of the final anneal. This has the effect of inducing a strong secondary growth into a material that will not normally support this type of secondary recrystallization.

Magnetic properties of highly oriented flat-rolled iron are given for sheet thicknesses from 6 to 25 mils. Comparisons of properties are made with 3% silicon iron and 50% cobalt—iron sheet.
Some Concepts Concerning the New High-Permeability 50–50 Nickel—Iron Alloys
Authors: Kang I. K. , Scholefield H. H. , Martin A. P.
Published: January 2005

A substantial increase in initial permeability as well as maximum permeability in 53% and 58% nickel—iron alloys after annealing at below the Curie temperature under a magnetic field was obtained. The permeability at 40 G was 38 000, and corresponding maximum permeability was 320 000. The response to magnetic annealing was observed to be dependent on secondary recrystallized textures, of which two kinds were observed. The texture of which the central cube pole of the cube texture rotated around [100] axis parallel to rolling direction showed good response to the magnetic annealing, while the texture of which the central cube pole of the cube texture rotated around [111] axis showed poor response to the magnetic annealing. The percentage increase of the permeability at 40 G is also shown to be dependent on the squareness of the hysteresis loop of specimens before the magnetic annealing. Increase in the permeability at 40 G could be explained by considering the relationship between the induced uniaxial anisotropy and the crystal anisotropy, and also by the reduced magnetostriction.
Metallurgy and Magnetic Properties Control in Permalloy
Authors: English A. T. , Chin G. Y.
Published: January 2005

The increasingly broad range of applications for the Permalloy family of magnetic materials has made them the object of intense and continuing study over the years. In this review, four main types of magnetic anisotropy are first discussed. These are the magnetocrystalline, magnetostrictive, thermomagnetic, and slip-induced anisotropies. It is pointed out that control of these anisotropies through composition selection and judicious processing procedures is the key to attainment of high initial permeability and squareness in the Ni–Fe–Mo–Cu system. Specifically, while zero anisotropy from all sources is the goal for high initial permeability, introduction of a nonzero anisotropy has proven effective in obtaining good squareness. The influence of metallurgical factors, in particular the role of crystallographic texture, is discussed.
Miniature Ferrite Cores
Authors: Brownlow J. M. , Grebe K. R.
Published: January 2005

Several performance advantages can be realized in ferrite memory cores by reducing the aperture size and the diameter ratio. Advantages which can be obtained are: lower drive currents, wider operating margins, lower back voltage, and greater packing density. The smallest cores produced by conventional core pressing technology have apertures of 180 μ and diameter ratios of 1.6. A new forming method has been developed for producing, in quantity, cores having apertures of 110 μ and diameter ratios of 1.36. Excess fragility is avoided by building the cores with two materials in concetric relationship. Both the inner magnetic layer and the outer nonmagnetic layer have thicknesses of 20 μ, leading to a physical diameter ratio of 1.7. In the process, a cylindrical monofilament is coated with successive layers of varnishes loaded with ferrite powders. Curing and cutting short lengths of this formed tubing produce green cores which are then fired to high temperature. The materials are chosen for compatibility of firing shrinkage, low interlayer reactivity, and zero magnetostriction. The inner magnetic layer has zero magnetostriction with the composition Fe1.62Mn0.80Cu0.45Zn0.10Bi0.02La0.01O4. The nonmagnetic layer is Fe1.20Mn0.78Cu0.30Zn0.70Bi0.02O4.
Magneto-Optic Detection of High-Density Recordings
Authors: Treves D.
Published: January 2005

The various noise sources in a high-density magneto-optic readout system are evaluated. It is shown that shot noise is not severe even at interrogation rates of 107 bit/sec and bit areas of 10−6 cm2. Various techniques used to reduce the noise originating from surface imperfections are described and their effectiveness demonstrated by experimental results.
Switching Properties of Europous Oxide
Authors: Ahn K. Y. , Shafer M. W.
Published: January 2005

Measurements of quasistatic and dynamic switching properties of EuO have been made. EuO was pressed in the form of toroidal cores, and fired at different temperatures to obtain a variety of grain sizes. The quasistatic switching properties measured at 4°K with a 105 cps drive field (H<100 Oe) show that the hysteresis loop is not square and the remanent magnetization Mr is typically 60% of saturation value. The coercivity Hc was shown to decrease with increasing grain size. For example, with a grain size increase from 55 to 220 μ, Hc decreases from 13 to 10 Oe (with H=50 Oe). Hc also decreases with decreasing drive field. The temperature dependence of Hc is similar to that of M but decreases at a slower rate for temperatures up to 63°K. The dynamic switching properties, when expressed in τ(H–H0) = S (τ is the switching time, H is the applied field, H0 is the threshold field, and S is the switching coefficient), of a typical sample with Hc=5 Oe (at H=30 Oe) are τ(H−20) = 2.5 μsec·Oe for H≥70 Oe and τ(H−12) = 3.1 μsec·Oe for H≤70 Oe at 4.2°K for 90% switching. At low field, the flux reversal appears to be dominated by domain-wall motion; at high field the flux may reverse by nonuniform rotation. In contrast to conventional ferrite materials, EuO has slower switching speed and, consequently, has few application possibilities as computer storage elements. However, the large value of M coupled with nonsquare hysteresis loop and the insulating property make this material attractive for use in a number of low-temperature applications.
DTPL—New Thin-Film Technique for Magnetic Logic
Authors: Spain R. J. , Jauvtis H. I.
Published: January 2005

Improvements in the technique of domain tip propagation logic (DTPL) have been made possible through the use of two coupled magnetic layers. The resulting increase in the forces of interaction between domain tips has led to the construction of reliable DTPL logic elements which operate over ±30% variations in drive field strength. The construction of film-film information transfer elements and noninteracting domain tip channel crossovers which greatly simplify the design of complex DTPL networks is described.