bluuebunny/crossref_metadata_2025 huggingface dataset:
Sublattice Magnetization in Several Rare-Earth and Yttrium Iron Garnets by Means of 57Fe NMR
Authors: Gonano R. , Hunt E. , Meyer H. , Harris A. B.
Published: April 2005

We have observed the NMR of 57Fe on the a and d sublattices of YIG, GdIG, and LuIG between 4° and 200°K. Using the spin-echo technique the frequencies could be determined to within a few kHz. For LuIG the determination of the frequency was less accurate due to the presence of the lutetium resonances which overlay the iron resonances. Assuming the frequency is proportional to the sublattice magnetization, the data were fitted to the equation derived from spin-wave theory. For YIG and LuIG inclusion of the T7/2 term was necessary to represent the data above 40°K. Using the theory of noninteracting spin waves we have derived expressions for the sublattice magnetizations in terms of the exchange integrals Jaa, Jad, Jdd, and J′ad, where J′ad describes interactions between next-nearest-neighboring pairs of spins on the a and d sublattices. Our experimental results indicate that Jaa and Jdd are not negligible. The T32 coefficients were found to be about 15% larger for LuIG than for YIG. Our value of the exchange stiffness constant of YIG is 10% larger than those determined calorimetrically and hence agrees with values determined by microwave instability measurements. For LuIG our value of this constant agrees with the specific heat value.
Magnetostriction of Dysprosium, Holmium, and Erbium Iron Garnets
Authors: Clark A. E. , DeSavage B. F. , Tsuya N. , Kawakami S.
Published: April 2005

The temperature and field dependences of the anisotropic magnetostriction coefficients of Dy, Ho, and Er iron garnets were measured from 78°K to room temperature. At the compensation points there is a reversal in the field-dependent magnetostriction (anisotropic forced magnetostriction) and a sharp dip in the apparent saturation magnetostriction. At high temperatures, the magnetostriction coefficients approach the values measured previously for YIG (≅10−6). At low temperatures, large strains arise because of the large magnetoelastic coupling of the rare-earth ion: λ100 (0°K) REIG/λ100 (0°K) YIG≅103; λ111 (0°K) REIG/λ111 (0°K) YIG≅50. Estimates of the 0°K magnetostrictions based upon the single-ion theory of magnetoelastic coupling are −1400, −930, and 420×10−6 for λ100, and −550, −220, and −300×10−6 for λ111 of Dy, Ho, and Er iron garnets, respectively. These values, although 50 to 1000 times larger than YIG, are one order of magnitude smaller than the enormous strains observed in the heavy rare-earth metals. This difference can be accounted for by the difference in elastic moduli and density of rare-earth ions. In both the metal and garnet the magnetoelastic coupling coefficient of the rare-earth ion is approximately 103 cm−1.
Induced Anisotropy of Silicon-Doped YIG
Authors: Hunt Robert P.
Published: April 2005

The induced anisotropy of single-crystal silicon-doped YIG (Y3Fe5−δSiδO12; 0≤δ≤0.18) was studied by means of a torque magnetometer. It was found that the annealed component of the torque could be adequately described by a free energy of the form Aan=−GΣ lim i>iαiαjβiβj,  i,j=x,y,zwhere αi and βi, respectively, specify the direction cosines of M during measurement and anneal.

A model consistent with these observations was formulated. Specifically, it was assumed that the annealed anisotropy was caused by an ordering of the Fe2+ ions over the four types of magnetically inequivalent octahedral sites. Taking into account the interaction of crystal field, spin-orbit, and exchange interaction, a calculation of the energy levels of the octahedrally coordinated Fe2+ ion provides an eigenvalue spectra compatible with the symmetry and magnitude of Aan.
Antiferromagnetic—Weak-Ferromagnetic Behavior in Aged Chromium—Rhodium Alloys
Authors: Booth J. G.
Published: April 2005

The magnetic susceptibilities of some aged Cr-Rh alloys show unusual properties when cooled from above 300°C in an applied field. An apparent ``frozen in'' moment of order 10−2 emu·g−1 appears on the result of an anisotropy which sets in at or near the temperature at which, for the same specimen cooled in zero field, a maximum in susceptibility occurs. Reverse fields up to 10 kOe are insufficient to reverse this moment. The remanent moment is also a function of aging time and disappears again when the alloy is completely precipitated. Resistivity measurements suggest that the anisotropy sets in at the Néel temperature of the matrix and the general character of the results may be interpreted as resulting from some type of exchange between the weakly ferromagnetic precipitate and the antiferromagnetic matrix.
Studies of Hyperfine Fields in Iron Alloys
Authors: Rubinstein M. , Stauss G. H. , Stearns M. B.
Published: April 2005

The 57Fe hyperfine field spectra of several bcc iron-rich binary alloys have been studied by the Mössbauer effect, the spin-echo technique, and by frequency-swept nuclear magnetic resonance. The alloys contained low concentrations of Al, Si, Mn, Cr, V, Co, or Ni. By computer analysis, the experimental spectra have been decomposed into component lines, assuming a model where the effects of the individual neighbor shells are additive. The resulting shifts in hyperfine fields due to the three nearest-neighbor shells obtained by the three techniques are compared and discussed.
Localized Moment of Dilute Fe in Iridium
Authors: Taylor R. D. , Steyert W. A.
Published: April 2005

The Mössbauer effect of 57Fe impurities in various host metals has proved to be a useful tool in determining any localized moment on the impurity. In general the results have been in good agreement with those obtained from susceptibility measurements for higher Fe concentrations. We report measurements on very dilute Fe in Ir taken over the range 1.1° to 300°K and 0 to 62 kOe applied field. These measurements yield s(J+1)/J=66±10°K and μ Hsat(J+1)/J=−188±30 μB−kOe, where J is the spin associated with the localized moment μ, Hsat is the internal field for fully aligned spins, and s is an interacting host field which tends to depolarize the spins being aligned in the external field. The quality of the fit does not allow an independent determination of μ; however, it certainly is not zero. Similar results were obtained for an Ir999Fe1 alloy. This is in contrast to recent susceptibility measurements where for this alloy no localized moment was found; susceptibility measurements on an Ir99Fe1 alloy indicate the presence of a localized moment.
Magnetostriction of Erbium Single Crystals
Authors: Rhyne J. J. , Legvold S.
Published: April 2005

The magnetostriction of Er single crystals has been measured from 300° to 4°K in applied fields up to 30 kOe. Standard strain gauge methods were used. The exchange magnetostriction which results from the application of a c axis field was determined in the quasiantiphase domain and modulated moment temperature region. Above the exchange critical field, the c axis expanded sharply, and the basal plane contracted isotropically. At 29°K, for example, the critical field was 5.5 kOe, and the c axis and a axis strains were 2.8×10−3 and −1.1×10−3, respectively. Below 20°K application of a field in the basal plane produced a sharp change in strain at 18 kOe. A maximum c axis strain of 1×10−3 was accompanied by a smaller nonisotropic contraction of the basal plane and a net increase in volume. Examination of the high-field dependence of the strain and magnetic moment data suggests that these results arise from a field-induced breakdown of the conical ferromagnetic structure into a conical fan state. The b axis strain was measured as a function of applied field angle, and from these data the second-order anisotropic basal plane magnetostriction constant was obtained. In accordance with theoretical predictions,1 negative values (e.g., −8.2×10−5 at 65°K) were found above 55°K. Below 18°K unexpectedly small and positive values (e.g., 7.2×10−4 at 4.7°K) were obtained, presumably due to the effects of the exchange magnetostriction. The temperature dependence of the a, b, and c axis strains in zero applied field and in a 30-kOe field was determined. The zero-field data show inflection points at the 85° and 55°K oscillatory magnetic state transitions and sharp discontinuities at the 18°K transition to the conical ferromagnetic state.
Effect of Assumed Electronic Configuration on the Electronic Band Structure of Nickel
Authors: Snow E. C. , Waber J. T. , Switendick A. C.
Published: April 2005

The electronic band structure of nickel has been computed by the APW method by using the atomic Dirac-Slater wavefunctions of the free nickel atom in five configurations of the general type 3d10−x4sx. Movement of the d and sp bands relative to each other occurs as a function of x, the assumed number of holes in the d states. The area of the neck at L is strongly dependent on x. A neck of sufficiently small area to agree with deHaas-van Alphen data is found only when 0.5<x≤1.0. It is shown that if there is a significant difference between the number of s-like electrons in the spin-up and spin-down bands when a magnetic field is applied, the topology of the two Fermi surfaces will be different.
Localized Impurity States in Metals: Dilute Solutions of Ni in Be
Authors: Klein A. P. , Heeger A. J.
Published: April 2005

Measurements of the residual resistivity as a function of solute concentration in dilute alloys of nickel in beryllium are reported. The resistivity data together with specific-heat measurements on similar dilute alloys of the same system determine the occupation number and level width of the virtual d-states on the nickel impurity. The results indicate that the number of d electrons per nickel atom is approximately 8.7, and that the virtual level width is about 0.4 eV. This relatively narrow width is to be compared with the much greater value of the Coulomb-exchange quantity; (U+4J)≃7 eV. The anomalously large residual resistivity for Ni in Be appears to be the result of the small number of carriers in the nearly filled band of Be.
Shiftless Fermi Level in Iron, Nickel, and Cobalt
Authors: Belson Henry S.
Published: April 2005

Walmsley has suggested a method whereby one can deduce the relative density of states at the Fermi level for spin-up and spin-down electrons. This method compares the shift in Fermi level with applied magnetic field for a magnetic metal with that of a nonmagnetic metal by measuring the voltage induced across the plates of a capacitor, one plate of which is of each metal. His measurements indicate that all Fermi surface electrons have moments parallel to the bulk magnetization. We have repeated and extended these measurements and get different results. We have measured the voltage induced in Fe-Al, Ni-Al, and Co-Al capacitors (evaporated magnetic metal on one side of a high-permittivity ceramic wafer and Al on the other) as a function of applied field. We have also measured a series of Fe-Cu capacitors of different thicknesses of iron, and a capacitor constructed of rolled iron foil and aluminized Mylar. Voltages appear which relate to the change of magnetization rather than to applied field. A magnetostriction-mechanical strain-piezoelectric voltage is consistent with these results. The only reliable data is thus that taken at high fields approaching or exceeding saturation. Local demagnetization or anisotropy in a thin film deposited on rough ceramic increases the field necessary for saturation, which may account for Walmsley's result. Thicker iron films show a decrease in these voltage changes and the foil capacitor shows essentially nothing. We find the shift in Fermi level in iron, cobalt, and nickel to be less than ½ μV/kOe at high fields, and the ratio of spin-up to spin-down density of states at the Fermi level to be less than 1.18.
Anomalous Superparamagnetism and Interface Effect
Authors: Kneller E. , Wolff M.
Published: April 2005

In precipitation alloys, a gradual transition of composition (interface) is expected between precipitates and matrix. Since the Curie temperature of solid solutions is a continuous function of composition, this implies that the effective volume Veff of ferromagnetic precipitates in a nonferromagnetic matrix, and the effective ferromagnetic packing fraction peff both depend on temperature (interface effect). It is shown that deviations of the superparamagnetic behavior of Fe-Ni-Cu alloys from that calculated for particles with constant volume and the maximum possible magnetostatic interaction effect, may quantitatively be accounted for by the interface effect. On account of the fact that the interface effect is proportional to the surface-to-volume ratio, and that this ratio at a given volume is for spheres smaller than for any other particle shape, a corresponding analysis of experimental data also permits to distinguish between spheres and other particle shapes.
The Chain-A New Magnetic Film Memory Device
Authors: Leilich H. O.
Published: April 2005

A copper strip plated with a nickel-iron film forms a new device for orthogonally switching word organized memories. The strip carries the word current. Bit-sense wires passing through holes in the strip determine the storage locations.

The device has closed flux in both word and bit directions, such that the film thickness, miniaturization, and bit packing density are not limited by demagnetization and stray field phenomena. Films of 25 000 Å thickness give signals of 500 mV·nsec which allow the use of slower rising read pulses and less gain bandwidth in the sense amplifiers relative to known thin-film devices. The configuration of the chain also enhances magnetic stability and permits nondestructive readout.

The characteristic impedance of the chain word line is strongly influenced by the film properties; stray fields and Ohmic losses are small. The bit-sense wire has a high impedance, very high bit density, and low attenuation; very large sense segments are possible.

The manufacture of chains can be done in a low-cost batch process, while the wiring of the array resembles the mass assembly process of ferrite core planes.
Sharp Films as Memory Elements
Authors: Barker P. D. , Torok E. J.
Published: April 2005

The concept of sharp films results from a study of the behavior of the magnetization vector at the edge of a thin film. In that study it was shown that many of the effects of the demagnetizing field at the edge of a film can be predicted by assuming a local shape edge-anisotropy field, whose easy axis lies parallel to the edge of the film. According to this theory, square films have a low nucleation threshold because the edges of the film perpendicular to the easy axis have an edge anisotropy that subtracts from the ordinary field-induced anisotropy yielding a region of low resultant anisotropy. Sharp films are memory elements in which the angle between the film edge and the easy axis is everywhere small. Consequently, the resultant anisotropy field along the edge is the sum instead of the difference of the two anisotropy fields, and the nucleation threshold is high. In fact, reverse domains in these films generally form in the center rather than at the edge. Sharp films have typical Hc values of 3 Oe for films of 4½ to 5 Oe Hk, while the reversible limit (creep threshold for zero easy axis field) will be 0.1 Oe less than H̄k.

Since magnetization creep is the principle limitation of thin film memory elements and since sharp films have creep thresholds far larger than films of ordinary shape deposited on the same substrate at the same time, new fast, low-power NDRO memory modes are possible with sharp films. These modes involve rotationally switching the films from one saturated state to another and use fields that are ⅔ Hc and ⅔ Hk so that no unselected films are disturbed.
Closed-Flux Thin Magnetic Film Memory Prepared by Electroplating
Authors: Eide J. E.
Published: April 2005

The bit density in an open-flux thin magnetic film memory is limited by stray and demagnetization fields. The effect of this field can be reduced by utilizing film memory elements in pairs, one on top of the other. Such a technique has been used with a ``hard'' magnetic upper film layer and a ``soft'' magnetic lower film layer. Prepared samples for test purposes consist of strips which were 1 in. long and 0.01 in. wide, located 0.02 in. apart from center-to-center. The strips have a 0.005-in.-thick electroplated copper wire running between the upper and lower magnetic films. The easy axis for both films is in the same direction perpendicular to the length of the copper wire. When tested in a NDRO mode the copper wire acted as a common digit sense line. The word lines are electroplated in such a way as to form a line pattern 90° to the common sense digit lines. An over-all bit density of 2500 bits per square inch has been prepared and pulse tested in a NDRO mode.
Coincident Current Magnetic Film Memories Using Locked Hard-Direction Films Having Microshape Anisotropy
Authors: Billing H. , Rüdiger A. , Schilling R.
Published: April 2005

Specially prepared NiFe films allow information storage in two hard-direction stable states. Most promising are films with very narrow strips of alternating thickness (e.g. D0=200 Å, D1=400 Å, strip widths b≈10 μ). The Néel wall forces, and the microshape anisotropy introduced by the strips of alternating thickness provide extremely stable locked magnetization states in the hard direction. A bias field forces the Néel walls to align along the thickness slopes, thus completely eliminating creeping. These unique magnetic properties can be utilized for coincident current selection and a nondestructive readout in memories of high storage capacity.

A readout method is employed using two orthogonal high-frequency fields of different frequencies fx and fy, providing an output signal at the difference frequency fm=fx−fy. The readout amplitude differs by two orders of magnitude, depending on the information stored. Pulse measurements with a number of these films showed the feasibility of the method. No deterioration of the output signals was observed even after 108 read, write, or half-select cycles. An evaluation of possible speed and storage capacity is made, taking into account various sources of noise and disturb signals.
Diodeless Magnetic-Film-Shift-Register Designs Utilizing Shifted Hysteresis Loops
Authors: Schmidt E. H. , Holmen J. O.
Published: April 2005

Improved diodeless magnetic shift registers have been designed which utilize electrolessly deposited Ni-Co-P films exhibiting shifted hysteresis loops. Hysteresis loop shifts along the H axis can be controlled during the deposition process or during an annealing process. Loops with coercivities unbalanced by ratios greater than four-to-one have been realized. This unidirectional anisotropy is stable over a large drive current and temperature range. The dynamic switching properties are not influenced by the magnetic state of the film. Diodeless magnetic-shift-register designs are discussed. Substantial reductions in circuit complexity and power consumption are obtainable and the operational tolerance is increased by these designs. This magnetic behavior is believed to result from a magnetic exchange interaction between separate phases in the deposited Ni–Co–P material. Mechanisms which explain this phenomena are proposed. Theoretical extensions of these effects to monostable hysteresis loops and multithreshold magnetic devices are also presented.
Electrical Transport Properties of the Insulating Ferromagnetic Spinels CdCr2S4 and CdCr2Se4
Authors: Lehmann H. W. , Robbins M.
Published: April 2005

Electrical transport properties were measured on the recently discovered ferromagnetic spinels CdCr2S4 (Tc=85°K) and CdCr2Se4 (Tc=130°K). The large Cr−Cr separation (≥3.63 Å) excludes metallic conductivity due to Cr−Cr overlap. Electrical conductivity, Seebeck effect, Hall effect, and magnetoresistance measurements were made on high-density, polycrystalline samples (CdCr2S4: 99.6%; CdCr2Se4: 99.9% of the theoretical density). Both materials show a negative temperature coefficient of the resistivity in the para- and ferromagnetic region without any discontinuity at the Curie temperature. The room-temperature conductivities of CdCr2S4 and of CdCr2Se4 are 5×10−4 (Ω·cm)−1. At 77°K the conductivity of CdCr2S4 is 3.5×10−10 (Ω·cm)−1 and of CdCr2Se4 6.7×10−5 (Ω·cm). The Seebeck coefficient for both materials is rather small: (CdCr2S4: −60 μV/°K; CdCr2Se4: +60 μV/°K), which indicates that the materials are almost compensated. The room-temperature mobility of CdCr2Se4 is 7 cm2/Vsec. In the ferromagnetic region CdCr2Se4 exhibits a negative magnetoresistance effect. An applied field of 7 kG results in a 4% increase of the conductivity. Band formation in CdCr2Se4 due to overlap of the 4p orbitals of the Se ions is proposed.
Magnetic Anisotropy in CoMnO3
Authors: Cloud W. H. , Jesson J. P.
Published: April 2005

Magnetization studies on an aggregate of single crystals of ferrimagnetic CoMnO3 oriented with their trigonal axes parallel gave a value of K1+2K2= −1.4/×107 erg/cm3 at 300°K for the magnetocrystalline anisotropy expressed in the usual form: K0+K1 sin2θ+K2 sin4θ. The very large anisotropy is believed to arise from partial removal of the orbital degeneracy of the 4T1 ground state by a trigonal component of the crystal field. The anisotropy energy was calculated following the method of Slonczewski except that the entire ground-state manifold was treated rather than using a perturbation approach. The fact that the moments lie perpendicular to the trigonal axis makes the more complete calculation necessary. The observed anisotropy energy was obtained for a trigonal splitting of 1250 cm−1 and a spin orbital parameter (αλ) of 204 cm−1. The sign of the trigonal splitting is such that an orbital singlet lies lowest.
Theory of the First-Order Magnetic Phase Change in UO2
Authors: Blume M.
Published: April 2005

A simple model accounts semiquantitatively for the first-order magnetic phase change observed recently in UO2 by Frazer, Shirane, Cox, and Olsen. The model assumes that the electronic structure of the paramagnetic U4+ ion consists of a nonmagnetic singlet ground state and a low-lying magnetic triplet, and that only bilinear isotropic exchange interactions are present. In a molecular-field theory the triplet is split by an internal field proportional to the magnetization. If the molecular field is sufficiently strong one of the components of the triplet will lie, in the magnetic state, below the singlet, and a self-consistent magnetic solution is obtained at T=0. Increasing the temperature causes the magnetization to be reduced, and the low lying component of the triplet is raised in energy. It is shown that a ``catastrophe'' may occur at some critical temperature so that the magnetization is reduced discontinuously to zero. It is also found that, depending on the ratio of the singlet-triplet energy difference to the molecular field splitting of the triplet, one obtains either no magnetic ordering, a first-order phase change, or a second-order transition.
Mössbauer Study of 57Co(57Fe) in CoO at High Pressure
Authors: Coston C. J. , Ingalls R. , Drickamer H. G.
Published: April 2005

The room-temperature internal magnetic field Hi, electric quadrupole coupling ε, and isomer shift IS of divalent 57Fe in CoO have been measured as a function of pressure up to about 250 kbar. Radioactive samples were prepared by heating 57Co-enriched Co3O4 in vacuum above 1000°C. The main features of the velocity spectra are qualitatively similar to those of the temperature study of this system as reported by Wertheim,1 except that the fraction of trivalent 57Fe observed is substantially reduced.2,3 As the pressure is raised the velocity spectrum unfolds into a magnetic hyperfine pattern in which Hi increases from zero to about 210 kOe at 250 kbar. This value is somewhat higher than the low-temperature saturation value of approximately 180 kOe. The rate of increase of Hi with pressure, coupled with low-temperature and x-ray pressure-volume measurements,4 shows that the Néel temperature TN (291°K at atmospheric pressure) increases with decreasing volume in a manner consistent with the results of Bloch et al.5 [d(lnTN)/d(lnV)≅ −3 at atmospheric pressure]. The velocity spectra also indicate small changes in both IS and ε with pressure, the former varying from −1.16 mm/sec at atmospheric pressure to −1.08 mm/sec at 250 kbar, relative to a stainless steel absorber. Both the change in IS and saturation value of Hi are consistent with an expansion of the 3d charge density and an accompanying increase in the 3s charge and spin density at the nucleus, because of less screening. The parameter, ε=¼e2qQ, in the antiferromagnetic phase is observed to approximately double from −0.03 mm/sec at 100 kbar to −0.06 mm/sec at 250 kbar. (These values are based on the unproven assumption that Hi is parallel to the axis of an axially symmetric electric field gradient tensor.)
Effects of Hydrostatic Pressure on the Magnetic Ordering Temperatures and the Magnetization of Some Ionic Compounds
Authors: Bloch D. , Chaissé F. , Pauthenet R.
Published: April 2005

We have measured the variation of the magnetic-ordering temperatures θ of CoO and of several ferrite garnets as a function of hydrostatic pressure up to 6000 bar. One observes that ∂(log θ)/∂(log V), where V is the volume, is of the order of −3.2. An analysis of the thermal variation of the paramagnetic susceptibility gave the same result. We have measured at room temperature the variation with pressure and field of the magnetization of some ferrite garnets; the observed results are related to the variation with pressure of the compensation and Curie points.
Growth of Europous Oxide (EuO) Single Crystals
Authors: Guerci C. F. , Shafer M. W.
Published: April 2005

The desirability of having large sound single crystals of EuO for a number of physical measurements has been well established. Although crystals of EuO had previously been grown, they were either of poor quality, primarily because of container contamination, or too small for many measurements. We report here on a method of growing large, single-phase, mechanically sound crystals of EuO. The method is one where growth takes place from a solution containing an excess of europium metal. The solution, sealed in molybdenum crucibles, is cooled from 1950°–2000°C at the rate of about 25°/h. Centimeter-size crystals were grown and shown to be of extremely good quality by an examination of their Laue spots and their microstructure. The crystals have a lattice constant of 5.1451 Å±0.0003 and a density of 8.180±0.002. The data from the crystal-growing experiments were used to propose a phase diagram in which EuO, when pure, is shown to be an incongruently melting compound.
Covalency Criterion for Localized vs Collective Electrons in Oxides with the Perovskite Structure
Authors: Goodenough John B.
Published: April 2005

In many oxides the outer d electrons are not localized, magnetic electrons but collective, metallic electrons either as a result of cation-sublattice band formation or of covalent mixing of anion p and cationic d states. It is shown that cation-sublattice band formation does not take place in oxides with ReO3 or perovskite structure and that they are therefore suitable for testing any covalency criterion for the magnetic vs metallic state. A parametric criterion is developed from physical arguments, and it is used to interpret systematically the magnetic and electric properties of oxides with the perovskite structure. The role of the Hartree—Fock intra-atomic exchange correlations is found to be important, and the physical origin of the ferroelectric transitions is identified.
Rare-Earth Compounds with the Th3P4-Type Structure
Authors: Holtzberg F. , Methfessel S.
Published: April 2005

Th3P4-type compounds occur in rare-earth systems with elements of Vth and VIth group of the periodic system. In general, the existence of Th3P4 compounds appears to be coupled with the formation of 1:1 compounds of the NaCl type in the same system. Analysis of I 4̄ 3d symmetry reveals certain similarities of atomic coordination and distances in both structures.

In RE3−xvxX4 (X=S, Se, Te) (0≦x≦⅓) the rare-earth ions occupy a defect Th3 lattice with a random vacancy distribution. With increasing vacancy concentration x, the materials change continuously from metals to insulators and interesting electrical, ferromagnetic, or superconducting properties have been observed. The Vth group elements, Sb and Bi, form metallic compounds without a homogeneity range and with the rare-earth ions on the P4 sites.
Magnetic Properties of the Terbium Oxides at Temperatures between 1.4° and 300°K
Authors: MacChesney J. B. , Williams H. J. , Sherwood R. C. , Potter J. F.
Published: April 2005

The six terbium oxide phases whose compositions range between Tb2O3 and TbO2 have been prepared and their magnetic properties measured at temperatures from 1.4° to 300°K. The lower oxide phases (C and B polymorphs of Tb2O3, TbO1.715, TbO1.809, and TbO1.823) were prepared by equilibration at appropriate temperatures and oxygen pressures. TbO2 could not be attained by equilibration with molecular oxygen, even at pressures as high as 4000 atm. Instead it was formed hydrothermally at 162°C and 306 atm of perchloric acid (HClO4·2H2O). X-ray diffraction confirmed the crystallographic parameters published by Baenzieger et al.1 for these phases.

Measurements of magnetization vs temperature revealed that all of the phases with the exception of TbO1.809 exhibited long-range magnetic order. Ordering temperatures are as follows: Tb2O3 (C type) 2°K, Tb2O3 (B type) 7°K, TbO1.823 6°K, TbO2 3°K. Except for TbO1.823 the ordering is antiferromagnetic as evidenced by negative paramagnetic Curie temperatures and absence of remanence effects. In the case of Tb1.823, however, a remanence amounting to 2% of the magnetization value at 80 kOe was observed upon removal of the field. All of the magnetically ordered specimens exhibited metamagnetic behavior; wherein at fields above a critical value (≈2 kOe), observed moments exhibited a nonlinear dependence upon applied field. In the paramagnetic region, the calculated effective moment was close to the appropriate free-ion value.
Nature of Exchange Coupling in Transition Metals
Authors: Herring Conyers
Published: April 2005

It is now fairly well accepted that the magnetic electrons of the d-shell transition metals must be viewed as itinerant. It appears, moreover, that they are only moderately correlated: although they occupy moderately narrow bands and have a spatial distribution similar to that of atomic d electrons, they fluctuate from atom to atom almost as randomly as the electrons of nontransition metals, thanks to the operation of various screening effects. In the exchange coupling of these electrons, their itinerancy plays a central role, and the concepts of the Heisenberg model are quite inapplicable. Significant contributions to the exchange coupling can arise both from polarity energy (the energy cost of having too many or too few electrons on an atom) and from the Hund's-rule coupling of electrons on the same atom. Correlation effects, though not strong enough to prevent sizable polar fluctuations, are very important in that they give rise to magnon modes, critical fluctuations, etc. Details of band structure are important in determining whether a metal prefers ferromagnetism, antiferromagnetism, or neither.
Magnetic Form Factor of Nickel
Authors: Hodges L. , Lang N. D. , Ehrenreich H. , Freeman A. J.
Published: April 2005

The magnetic form factor of Ni is calculated using the pseudopotential method, the ferromagnetic interaction being supplied by a parametrized Hubbard—Kanamori Hamiltonian. This approach is useful in the present instance because the form factor is primarily determined by uncompensated majority spin electrons near the Fermi surface where LCAO d-band functions represent a reasonable approximation for the wave functions. The asphericity of the d-electron spin distribution as well as the constant negative polarization of electrons in the outer regions of the unit cell observed by Mook and Shull are reproduced. The latter effect is accounted for by a reversal of the s-spin polarization in that region of the unit cell. A possible contribution due to a slow spatial variation of the spin polarization over the unit cell associated with compensated d electrons throughout the d band is also discussed.
Wick's Theorem for Spin Operators and Its Relation to the Coupled-Fermion Representation
Authors: Wang Yung-Li , Shtrikman S. , Callen H.
Published: April 2005

It is shown that Wick's theorem and the linked diagram expansion theorem for S = ½ operators (applied elsewhere by the authors to discuss antiferromagnetic spin waves) can be derived by a direct application of conventional theorems to the coupled-fermion representation of spin operators.
Mechanism for the Direct Exchange Interaction of Europium in Compounds with Rocksalt Structure
Authors: Smit J.
Published: April 2005

From the strong decrease in the nearest-neighbor exchange interaction going from EuO to EuS, EuSe, EuTe, it has been concluded that this positive interaction must be caused by direct orbital overlap. Since the 4f cores are very small, this has to occur via partial occupation of outer orbits. The excitation to the 5d wave function by zero point lattice vibrations has been considered and is thought to be responsible for the ferromagnetism of these compounds. The order of magnitude has been estimated and agrees with experiment.
Structural and Magnetic Characteristics of Annealed Electrodeposited Permalloy Films
Authors: Chang J. T. , Von Neida A. R. , Calbick C. J.
Published: April 2005

Electrodeposited uniaxial Permalloy films 10 000 Å thick were annealed for 3 min at temperatures up to 400°C in an easy direction field greater than Hk. Dispersion, α90, increases from 1.8° as plated to about 3.3° with annealing at 325°C. In the same temperature interval, skew and Hk remain unchanged. Above 325°C the magnetic properties change rapidly towards isotropic behavior. The onset of this effect is correlated with a large change in crystallite size. Transmission electron micrographs show a small increase in crystallite size D from 150 Å as-plated to 500 Å for annealing at 325°C, and a rapid size increase thereafter. The data for the change in α90 with D does not agree with theoretical predictions of Hoffmann; experimentally α90 is found to be proportional to D0.5 for annealing to 325°C.
Magnetic Properties of Layered Iron-Nickel Films
Authors: Morrison R. D. , Hanson M. M. , Oberg P. E.
Published: April 2005

A study of layered vacuum-deposited Fe–Ni films was made with varied layer thickness (15 to 180 Å) and deposition temperature (300° and 350°C); average film composition was held to a nominal value of 25% Fe. Magnetic property measurements included total flux, coercivity, magnetostriction, anisotropy field, and dispersion. Composition was determined by x-ray fluorescence and physical thickness by inter-ferometry. As expected, a lower limit of layer thickness (∼20 Å for 300°C substrates, ∼30 Å for 350°C substrates) has been observed below which the films have properties comparable to the nominally homogeneous films from a normal evaporation. At the other end of the range, a thickness is reached where interdiffusion of layers is negligible and further increase in layer thickness produces negligible change in properties. Variation of properties between these two extremes of layer thickness was used to obtain information about diffusion rates in the films and the effect of composition inhomogeneities on magnetic properties. Experimental results indicate that the equivalent rate constant associated with diffusion during deposition is consistent with a vacancy or surface mechanism and differs widely from high-temperature diffusion constants. Of the magnetic properties measured, dispersion and magnetostriction yield the most significant information regarding the relationship between magnetic properties and the extent of interdiffusion. The results show that composition homogeneity normal to the film surface will result only when the source vapor has the correct composition when averaged over any time interval corresponding to a film thickness no greater than 20–30 Å.
Magnetic Properties Observed During Vacuum Deposition of Permalloy Films
Authors: Ahn K. Y.
Published: April 2005

The quasistatic magnetic properties of vacuum-deposited Permalloy films of zero magnetostrictive composition were continuously monitored during deposition and substrate heating and cooling period in an evaporator equipped with a laser-operated Kerr magneto-optic hysteresigraph and a quenchable substrate holder in the temperature range of −196° to ∼400°C as a function of thickness up to ∼2000 Å. Films deposited at liquid-nitrogen temperature exhibit low (∼3 Oe) coercive force, with a very square loop, at thicknesses as low as 25 Å; this decreases rapidly with thickness increase. Films deposited at elevated temperature, for example 300°C, exhibit high (>20 Oe) coercive force with a very rounded loop when first observable at about 100-Å thickness. This, however, plummets downward sharply near 150-Å thickness, the loop meanwhile becoming square. The room-temperature coercive force of films deposited at high temperatures is more than that measured during deposition, while that of films deposited at liquid-nitrogen temperature drops as the film attains room temperature. In general, no change in Hc is observed upon exposing the fresh film to air at room temperature. The 2000-Å low-temperature films (deposited at −196°C) exhibit a well-defined uniaxial anisotropy of ∼6 Oe. This anisotropy field decreases monotonically on heating after deposition. At room temperature, Hk becomes ∼4.5 Oe. Upon further heating, Hk decreases to <1 Oe at 335°C. At 350°C a new easy axis with Hc∼1 Oe is rapidly induced by the applied magnetic field along the previous hard axis. This coercivity increases to >2 Oe when the film is cooled to room temperature. Smaller changes in Hk are observed upon cooling in films deposited at temperatures above 200°C. Some results on anisotropy spectrum are discussed.
Stripe Domains in Oblique-Incidence NiFe Films
Authors: Baltz Alfred
Published: April 2005

Stripe domains have been observed in NiFe films of various compositions evaporated at oblique incidence. The compositions ranged from 35% Ni to 92% Ni. The angles between the vapor source and the substrate normal were 0°, 30°, 60°, and 80°. Stripe domains were observed in all films evaporated at angles >30°. The domain width ranged from 600 to 9000 Å. Hysteresis loops were obtained in the plane and perpendicular to the plane of the films. Torque measurements were made to determine the rotatable anisotropy in the films.
Flux Reversal in Single-Crystal MnBi Films
Authors: Chen D.
Published: April 2005

Single-crystal MnBi films of thickness ranging from 2500 to 260 Å were grown epitaxially on mica substrates by vacuum deposition followed by a prolonged annealing procedure. The c axis of these films is perpendicular to the plane of the film. Magnetic hysteresis in the direction along the c axis has been measured by both the magneto-optic method and the torque magnetometer technique. The hysteresis loop shows an abrupt decrease in magnetization as the field is reduced from positive saturation to a critical value. This critical field is positive in films thicker than 1200 Å. The coercive force of the films varies from 200 Oe to 2 kOe as film thickness decreases. The thickness dependence of magnetic hysteresis was also measured on a 2400-Å film by repeated etching down to 1000 Å. The general characteristics are the same as measured on films of different prepared thickness. This thickness dependence of coercive force is in agreement with the theoretical result calculated from domain theory assuming a stripe domain configuration. The field required to saturate the films is 3.7 kOe and is approximately identical for all films. The dynamic flux reversal properties of these films were measured using a magneto-optical technique. The switching coefficient Sw was found to be 0.067 Oe·sec. These experimental results suggest that the flux reversal in these films is not by domain rotation, but by the motion of the domain wall.
Propagation of Transverse Domain Walls in Thin NiFeCo Films
Authors: Shafer P. E.
Published: April 2005

A new phenomenon of straight transverse domain walls has been observed in longitudinal propagation of walls in thin films. When the drive field is sufficiently large, the domain wall is observed to become nearly straight losing the jagged configuration typical of static transverse walls. If the drive field is rotated away from the longitudinal direction, the direction of propagation rotates the opposite way, but the wall remains straight. A model is suggested, relating the transverse component of external field near a skewed domain wall and the coherent rotation threshold in the material to the observed wall motion phenomena. The films were NiFeCo,1 nonmagnetostrictive, vacuum-evaporated on glass substrate, and 1000 to 3000 Å thick. The cobalt content was varied from 5% to 35%. The measured anisotropy, nucleation,1 and wall motion fields ranged, respectively, 6 to 40 Oe (Hk), 5 to 20 Oe (Hs), and 2 to 5 Oe (H0), the values in each case increasing with increasing cobalt content. Longitudinal domain wall velocities up to 5000 m/sec were observed. The velocity-drive field relation is strongly curved, lying between V=kH2 and V=kH3. The value of wall motion field (H0) does not appear to be directly related to the velocity-field curve, and H0 clearly does not act as subtraction from H.2 Wall velocity is sensitive to film thickness and composition, increasing with thickness and decreasing with increasing cobalt content.
Electron Microscopic Observation of Domain Wall-Inclusion Interactions in Iron
Authors: Johnson Charles A. , Glenn Richard C.
Published: April 2005

Transmission electron microscopic observations of the dynamic behavior of domain walls in thin polycrystalline foils of iron containing inclusions of varying sizes have been carried out under conditions of known applied field.1 The field component in the plane of the specimen was varied over the range 0→±10 Oe, traversing hysteresis loops in times of the order of 10 sec.

The observations show that inclusions affect the mobility of domain walls not only through the formation of individual Néel spike domains, but also by acting as tie points for domain wall intersections and by the formation of ``ladder'' domain structures connecting closely spaced inclusions.

The detailed domain structures observed during the cutting of large (about 1 μ) inclusions by 180° domain walls correspond closely to the structures predicted by detailed theoretical models of this process.2

New domains are readily formed at grain boundaries. A frequently observed alternative to the cutting of an inclusion by a domain wall is the formation of one or more new domains in other parts of the same grain.

Continuity of the normal component of magnetization across grain boundaries is accomplished either by echelon structures of the sort observed in thin nickel platelets3 or by individual spike domains extending from the boundary. A 16-mm motion picture film illustrating these points has been prepared and was presented at the conference.
Cu, Ni, Ag, and Fe Densities of States
Authors: Spicer W. E.
Published: April 2005

An experimental method for determining the densities of states in solids based on photoemission and optical measurements is described and illustrated with data from Cu and Ni. Densities of states for Cu, Ag, Ni, and Fe determined by this technique are presented. The Cu density of states is found to be in reasonable agreement with the band calculations of Burdick except for the appearance of a rather large peak in the experimentally determined density of states 6.2 eV below the Fermi surface. The Ni density of states is dominated by a strong maximum 4.5 eV below the Fermi level. This maximum is not predicted either by recent band calculations or by the rigid band model using the Cu density of states. Recent suggestions of Phillips and Mott concerning this are outlined.
Stripe Domains in Thin Magnetic Films and Their Application to Magneto-Optical Displays
Authors: Spain R. J. , Fuller H. W.
Published: April 2005

A thin magnetic film display element is described which consists of a planar, hermetically sealed unit containing a RIS 1 magnetic film and an overlying colloidal suspension of iron oxide. The effect of the ``stripe'' domain structure of the magnetic film upon the colloid is such as to furnish an element which is capable of diffracting light incident upon the surface of the element in a manner similar to that of a diffraction grating. The interference phenomena are, however, controllable by a magnetic field applied so as to cause changes in the distribution of the magnetization within the film. Both the intensity and color of the diffracted light can be modified by the applied field and such modification, once produced, is permanent until subsequent alteration is required. Command of the element can be accomplished by coincident drive currents in matrix fashion as is common in the operation of planar magnetic memories. Measurements performed on experimental RIS 1 display panels indicate an element switching speed of less than 10 μsec, a brightness of over 30 ft·L and a contrast ratio of greater than 70:1. The feasibility of manual entry of information and electrical read of the latter has been demonstrated as well.
Structure and Magnetic Properties of Dy2Mn4O9
Authors: Nowik I. , Williams H. J. , Van Uitert L. G. , Levinstein H. J.
Published: April 2005

Single crystals of Dy2Mn4O9, a new rare-earth transition metal oxide, were grown by a three-component flux method. X-ray studies indicate that the space group of this crystal is Pbam and the dimensions of the orthorombic unit cell are; a=7.24, b=8.44, c=5.62 Å. Magnetization measurements at 1.3° to 300°K in a magnetic field of 14.2 kOe show that an antiferromagnetic transition takes place in Dy2Mn4O9 at about 8°K. Large magnetic anisotropy is observed, the easy direction of magnetization lying along the a axis. At 4.2°K in a field of 100 kOe the magnetization along the c axis is less than 50% of that along the a-axis. In Mössbauer studies of the 26-keV γ-transition in 161Dy typical paramagnetic relaxation spectra were observed, from which the ``g'' tensor of the ground stark level of the Dy3+ ions was deduced; gz=18.5gx≈0, gy≈0. The spin-relaxation time of the Dy ions at 5°K was estimated to be 2×10−9 sec.
Magnetic Structure of EuTiO3
Authors: McGuire T. R. , Shafer M. W. , Joenk R. J. , Alperin H. A. , Pickart S. J.
Published: April 2005

Europium titanate has the cubic perovskite structure containing divalent Eu (7 μB) and tetravalent Ti. From magnetic measurements we find that EuTiO3 is one of the few antiferromagnetic materials with a positive θ (TN=5.3°K, θ=3.8°K). At 1.3°K the magnetic moment (σ) increases linearly with field to 10 kOe; above 14 kOe the moment saturates and σ=156 emu/gm (6.93 μB) at 20 kOe. Powder neutron-diffraction work indicates that EuTiO3 has the Type G magnetic structure in which a given Eu++ has six nearest-neighbor europium ions antiparallel and 12 next-nearest-neighbor europium ions parallel. In a perovskite structure where only the 12-coordinated ion is magnetic, i.e., Eu++, the molecular field relations for a two sublattice model yield J1/k=−0.021°K, where J1 is the effective intersublattice exchange interaction, and J2/k=0.040°K, where J2 is the effective intrasublattice exchange interaction. The signs of J1 and J2 are opposite to those found in the europium chalcogenide series. The chalcogenides, however, have the rocksalt structure in which the number of 90° cation-anion-cation interactions differs from the perovskite structure.