bluuebunny/crossref_metadata_2025 huggingface dataset:
Influence of Magnetic Order on Conduction Electrons and Phonons in Magnetic Semiconductors
Authors: Baltensperger W.
Published: February 2004

Magnetic correlations influence the energy of conduction electrons through the exchange coupling. A magnetization leads to a splitting of the band where, however, the states of the higher band are unstable against spin-flip with spin-wave production. The rather unknown ion-position dependence of the spin Hamiltonian couples the spins to the phonons. For weak spin-spin couplings an adiabatic principle is assumed. The effect of spin order on the phonon frequency, on the infrared and Raman spectra, and the isotope effect of magnetic couplings is discussed.
Rare-Earth-Compound Permanent Magnets
Authors: Becker J. J.
Published: February 2004

Since the discovery of the extremely high magnetocrystalline anisotropy of YCo5 in 1966 there has been rapidly increasing interest in the development of cobalt-rare-earth intermetallic compounds as permanent magnet materials. The observed coercive forces are still only a small fraction of the anisotropy fields, and for some reason the coercive forces attainable with SmCo5 are larger than in other isostructural compounds with comparable anisotropy fields. A number of experiments have shown that the coercive force is very closely related to and can be profoundly influenced by the nature of the particle surface. The processing of these materials into magnets can be approached in several different ways, with due regard to the problem of chemical stability. The long-range prospects of these materials may well be related to the improvement of the properties of compounds other than SmCo5 by influencing the factors that control the magnetization reversal process.
Magnetic Properties of Stable Dispersions of Subdomain Magnetite Particles
Authors: Kaiser R. , Miskolczy G.
Published: February 2004

Stable colloidal dispersions of subdomain-size magnetic particles have been prepared that retain their liquid characteristics in the presence of a magnetic field. Magnetization versus applied field curves were obtained as a function of particle size and volumetric solids concentration for magnetite dispersions in a wide variety of carrier liquids. The magnetic properties of these colloidal dispersions have been corrolated by superparamagnetic theory in terms of the size distribution of the suspended particles and their volumetric concentration, correcting for the formation of a nonmagnetic surface mantle one-unit-cell thick.
Application of Stoner Theory to Ferromagnetic ZrZn2-x Alloys
Authors: Knapp G. S.
Published: February 2004

We have studied the magnetic properties of a series of ferromagnetic alloys of ZrZn2−x, where x varies from 0.05 to 0.2. We found that the Stoner theory of ferromagnetism was consistent with the data taken below Tc for all samples. Above Tc, however, the susceptibilities obeyed Curie-Weiss laws, χ∝[1−(T/Tc)]−1, and not χ∝[1−(T2/Tc2)]−1, as expected from the Stoner theory.
Electron Spin Resonance in Ferromagnetic Sc3+xIn Alloys
Authors: Dunifer G. L. , Knapp G. S. , Corenzwit E.
Published: February 2004

We report the observation of electron spin resonance (ESR) in ferromagnetic Sc3+xIn. This material shows a strong narrow peak in the total magnetization as a function of x, with ferromagnetism occurring at low temperatures for x in the range of 0.10–0.20. We have studied the ESR properties of thin polycrystalline plates for several values of x lying both within and also outside the ferromagnetic region. Measurements were made at 12 and 18 GHz as a function of temperature. The temperature range extended from 1.3 to 50 K (several times the maximum Curie temperature, Tc, of 7 K). The g-value (corrected for demagnetization effects) is 2.02±0.01 at 1.4 K and appears to decrease to approximately 1.99 at the highest observable temperatures. The minimum linewidth occurs at Tc and increases slightly at lower temperatures. For T>Tc the line broadens rapidly with increasing temperatures. A comparison of the ESR linewidth with the reciprocal of the total magnetization as a function of temperature shows that even though both have the same qualitative type of behavior, the quantitative agreement is not as good as that predicted by the theory of exchange enhancement of spin lifetimes. Although one might normally expect a rather fast relaxation rate for the electrons of such an alloy, it appears that the small g-shift and a form of exchange enhancement are important for substantially increasing spin lifetimes and producing narrow lines at low temperatures.
Magnetic Field Dependence of the Specific Heat of Dilute Pd–Co, Pt–Co, and Pd–Mn Alloys
Authors: Boerstoel B. M. , Van Baarle C.
Published: February 2004

The specific heat of dilute alloys of the type palladium-cobalt has been measured in the temperature range from 1.2 to 30 K in external magnetic fields up to 30 kOe. Due to a high accuracy detailed results have been obtained. The excess specific heat appears to be strongly affected by magnetic fields. A comparison between palladium and platinum alloys reflects the smaller exchange enhancement in platinum. Preliminary results on dilute alloys of manganese in palladium show a striking difference between this element and cobalt and iron, when dissolved in palladium.
Exchange Enhancement of Conduction Electron Spin Lifetimes in ZrZn1.9
Authors: Walsh W. M. , Knapp G. S. , Rupp L. W. , Schmidt P. H.
Published: February 2004

The magnetic resonance originally observed by Ogawa in the ferromagnetic regime of ZrZn2 powder has been reinvestigated in thin plates of ZrZn1.9 of maximal Curie temperature and magnetization, at several microwave frequencies and over a wide temperature range extending well into the paramagnetic region. A g-value g = 1.98±0.01 is found at all frequencies and temperatures when demagnetization effects are taken into account. Well above the Curie temperature the resonance broadens rapidly and independently of frequency, following the Curie-Weiss behavior of the susceptibility. We attribute this width entirely to lifetime (spin-lattice) broadening as in the conduction electron spin resonance of normal metals but here subject to strong exchange enhancement. The deduced ``uncoupled'' relaxation time is crudely consistent with an estimated transport collision frequency and the degree of spin-orbit coupling indicated by the small g shift. Extrapolation of the relaxation mechanism into the ordered regime predicts a linewidth proportional to the observation frequency roughly as observed, through an additional orientation dependent broadening contribution appears at the lowest temperatures.
Ferrimagnetic Compositions in the System Fe1+xCr2−xS4
Authors: Robbins M. , Wolff R. , Kurtzig A. J. , Sherwood R. C. , Miksovsky M. A.
Published: February 2004

Materials in the system Fe2+Fex3+Cr2−xS4 have been prepared between x=0 and x=0.5. All of the compositions form with the spinel structure. Curie temperatures increase with increasing Fe3+ from 180°K for FeCr2S4 to 302°K for Fe12+Fe0.53+Cr1.5S4. Magnetic data suggest an ionic distribution of Fe1−x2+Fex3+[Fex2+Cr2−x]S4. From low-temperature resistivity measurements, it appears that all of the materials are semiconductors.
Multiplet Structure in the Reflectance Spectra of Europium Chalcogenides
Authors: Dimmock J. O. , Hanus J. , Feinleib J.
Published: February 2004

The ferromagnetic semiconducting europium chlacogenides exhibit two strong reflectance peaks arising from 4f–5d transitions of the Eu+ + ion which are split by a strong crystal field. The lower peak corresponds to transitions from the 4f7(8S7/2) ground state to the 4f6(7FJ)5d(T2g) configuration, whereas the higher energy peak corresponds to transitions to the 4f6(7FJ)5d(Eg) configuration. The structure and polarizations of the peaks in a magnetic field are analyzed in terms of the transition probabilities for right and left circularly polarized radiation taking into account (i) the multiplet structure of the 4f6(7FJ) configuration, (ii) the spin-orbit splitting of the 5d level, (iii) a phenomenological exchange field which acts on the 5d electron spin in the ordered phase, and (iv) the Zeeman splitting due to the domain orienting magnetic field.
Magnetic Behavior of MnCr2S4 in High Magnetic Fields
Authors: Denis J. , Allain Y. , Plumier R.
Published: February 2004

Magnetization curves obtained by pulsed field techniques in MnCr2S4 at low temperatures display two types of transition. At magnetic fields of the order of a few tens of kilo-oersteds, a transition from a Néel structure to a Yafet and Kittel one is occurring. At a field of about 105 Oe, another transition takes place between a Yafet and Kittel structure and a collinear one where the magnetic moments of the nonequivalent A sites may be different in length and sign.
Preparation and Properties of Ferromagnetic Bronze-Iron Composite Materials
Authors: Swisher J. H. , Fuchs E. O.
Published: February 2004

A combination of powder metallurgy and wire drawing techniques was used to prepare composite materials consisting of fine iron fibers in a 5% Sn bronze matrix. In addition to being ferromagnetic, the materials have excellent mechanical properties and corrosion resistance. Property data are reported on alloys containing 2.0, 5.6, 9.9, and 14.3 vol % Fe. The 9.9 vol % Fe alloy, after 99.9+% reduction in area, has a coercive force of 320 Oe, a remanent induction of 1800 G, and a hysteresis loop squareness, Ir/Is=0.85. The tensile strength of the same alloy is 156 000 psi (1077 MN/m2) and its corrosion rate in a solution of 5% NaCl in H2O is not measurably different from the bronze matrix material. The magnetic and mechanical properties are easily controlled by varying the amount of cold working. The magnetic properties attained are within the range of applicability for magnetic recording, and with modest improvements in properties, the alloys could be used in other applications for hard magnetic materials.
Transition Region in Recorded Magnetization Patterns
Authors: Curland N. , Speliotis D. E.
Published: February 2004

Various theoretical approaches have been recently offered to describe the writing and demagnetization processes in magnetic recording. All invariably correlate their calculations with readback pulse measurements, thus clouding their results with the dominant readback losses. In this paper a self-consistent iterative approach was used to calculate the demagnetization in an isolated recorded transition between two areas of opposite magnetization, as a function of the coercivity, remanence, and thickness of the recording medium. Lorentz transmission microscopy was used to verify the predictions of the theoretical calculations. For this purpose, a series of thin magnetic films of different magnetic properties and thicknesses were prepared and then recorded with an inductive-type transducer. The magnetization transition regions were observed to resemble a sawtooth structure. The walls of the sawtooth were inclined towards the easy magnetization direction, and the magnetization on either side of these walls was not equinormal. The size of the sawteeth varied with the magnetic properties and the thickness of the films. The average height of the sawteeth correlated well with the theoretically predicted transition regions.
Switching Dynamics for an Interacting Anisotropic Dipole Pair of Arbitrary Bond Angle
Authors: Bertram H. N. , Mallinson J. C.
Published: February 2004

The switching dynamics for a pair of identical uniaxially anisotropic dipoles of arbitrary bond angle is calculated for the case of the applied field coincident with the common anisotropy axis. Recently, we presented the nucleation fields (as a function of bond angle and interaction strength) which were derived by following the system quasi-statically from initial saturation to the first unstable equilibrium. Here, with these fields as initial conditions, we use the dynamic Gilbert equations to follow the precession of the moments to a stable equilibrium state. For the two possible final configurations, parallel or nearly antiparallel moments, an interaction strength-bond angle plot gives regions where these states are accessible. These regions are only moderately dependent on interaction strength. For small bond angles (with respect to the anisotropy direction) the moments rotate incoherently to the low-energy parallel state. For large bond angles the moments are constrained to rotate coherently to the parallel state. At intermediate bond angles the moments rotate incoherently to a stable antiparallel state. These conclusions are found to be independent of the dynamic damping parameter.
Analysis of Write Field Distribution in Permalloy Recording Head
Authors: Lin Y. S. , Tolaba J. H.
Published: February 2004

The magnetization and the write field configuration in permalloy heads are analyzed based on the micromagnetic torque equation. Instead of solving the nonlinear integro-differential equation directly, Fourier method is used to simplify the computation of the magnetostatic term. The method is esentially an extension of Dove's,1 by taking into account both the exchange coupling and the air gap. The equilibrium state for the magnetization and its induced stray field around the air gap must be solved for by the inversion of an N×N matrix (N=number of harmonics for the Fourier series), arising from the N linear equations approximating the nonlinear differential equations. The magnetization configuration in the head and the write field (both longitudinal and transverse) distribution are calculated as functions of air gap length, film thickness, anisotropy field of the film, magnetic path length along the head, and drive current, etc. Finally, a number of applications for the present method are also indicated.
Semihard Magnetic Alloys of Co–Fe–Nb System
Authors: Sasaki Tatsuji , Okada Masanori , Kassai Makoto , Henmi Zenzo
Published: February 2004

Ductile alloys of the Co–Fe–Nb system in the vicinity of 90% Co were studied for reed switch applications. Wires have been investigated which have high values of coercive force, squareness ratio and remanence as well as high stability of these magnetic properties against heating. As a result of this research, an 85 Co–12Fe–3Nb wire, 0.5 mm in diam., subjected to a sequence of a 1100°C intermediate anneal, 90% cold reduction and 750°C aging is deemed best for this application. This wire shows a coercive force of 20 Oe, a squareness ratio of 0.95 and a remanence of 15 000 G. Intermetallic Co–Nb compounds precipitate during aging treatment. This phenomenon causes the coercive force to increase. The cold drawing facilitates the precipitation. The intermediate anneal temperature should be sufficiently high to realize a complete solid solution in the wire. The drawn wire has 〈111〉 fiber texture. Since 〈111〉 is an easy magnetization direction, the wire shows a good rectangular hysteresis loop along the axis. This texture remains the same up to 900°C anneal. Some wires of these alloys are used for semihard magnetic reed switches in various electronic equipment such as control devices and electronic switching systems.
Further Magnetic and Thermal Studies of Cast Rare-Earth Permanent Magnets
Authors: Nesbitt E. A. , Chin G. Y. , Gallagher P. K. , Sherwood R. C. , Wernick J. H.
Published: February 2004

Studies have been made of the effect of composition on the magnetic properties of arc-cast alloys in the vicinity of Co3.5CuFe0.5Ce. The residual induction varies from 4000 to 6400 G with intrinsic coercive force values from approximately 5000 to 12 000 Oe. The maximum energy product values range from about 4 to 10×106 G Oe, the higher values generally associated with alloys of lower copper content. Freezing points of these alloys were determined for the first time using differential thermal analysis. Solidification occurs over a range of temperatures; initial freezing point decreases from 1177°C for a low copper alloy (Co3.94Cu0.5Fe0.56Ce) to 1124°C for a high copper alloy (Co2.63Cu2.0Fe0.36Ce). Several additional peaks were observed in the cooling curves after the initial freezing had occurred. These peaks are tentatively attributed to additional phases which are likely in view of the complexity of the Co–Ce and Cu–Ce binaries. The precipitation reaction at 400°C which was previously observed by metallography was evidently too weak to be detected in the DTA analysis. Measurement of magnetization versus temperature indicated that Curie temperatures are generally above 700°C depending on composition and heat treatment.
Relation between NMR Properties of 31P in the Paramagnetic State of the UP1−xSx System and the Magnetic Ordering
Authors: Kuznietz Moshe , Baskin Yehuda , Matzkanin G. A.
Published: February 2004

The UP–US solid solutions have a NaCl-type structure, are good conductors of electricity, and show systematic changes in the paramagnetic Curie temperature θ and the magnetic ordering (from antiferromagnetic type-I in UP to ferromagnetic in US). These changes are accounted for by RKKY-type interactions. NMR measurements, made on 31P in the paramagnetic state of the UP1−xSx system, are related to the magnetic ordering. There is good consistency between the NMR linewidths and the free induction (Bloch) decay-time constants, and between the echo decay-time constants and the calculated internuclear dipolar linewidths. The Knight shift K is linear in the susceptibility with a slope of (4.0±0.5) (mole/emu), that is independent of x, and does not reflect the changes in θ and magnetic ordering, thereby disqualifying the simple RKKY model for K. The spin-lattice relaxation time T1 increases with temperature T for all compositions, regardless of the magnetic ordering. T1T is empirically related to K differently in the antiferromagnetic and ferromagnetic compositions. The T1 results are discussed in terms of recently proposed models for nuclear relaxation due to indirect interactions with the localized magnetic moments via the conduction electrons.
NMR Observation of Domain Structure in Antiferromagnetic MnO
Authors: Christensen C. R. , Guenther B. D. , Daniel A. C.
Published: February 2004

The frequency pulled 55Mn nuclear resonance1 in MnO at 4.2°K was observed as a function of the angle of rotation of the applied field H0 about a [111] direction. The resonance spectrum was found to consist of one branch, independent of the position of H0, and three other branches which coincide in frequency with the angle independent branch at 60° periods and move to lower frequencies at other positions of H0. These branches correspond to resonance in antiferromagnetic T-domains ordered along the four equivalent [111] directions. The components of H0 perpendicular to each of the [111] directions were calculated as a function of magnet angle. The pulled resonance frequencies corresponding to these components of H0 agree well with the observed dependence of the four branch frequencies on the angle of rotation of H0. This dependence of the resonance frequency on the components of H0 in the {111} planes provides additional evidence that the pulled nuclear resonance mode is associated with the weak {111} plane anisotropy.
Longitudinal Relaxation of 57Fe Nuclei in Yb-Doped YIG
Authors: Myers S. M. , Meyer H. , Remeika J. P.
Published: February 2004

Measurements of T1 for Fe57 nuclei in Yb-doped YIG are reported for the temperature range 1.3–140 K, with the magnetization along the [111], [100], [110], and [112] crystallographic directions, respectively. These results are interpreted in terms of the ``slow relaxation theory,'' and are correlated with the ferromagnetic resonance work of Clarke, Teale, and Tweedale, whose data have been reanalyzed by us. Both sets of data can be represented fairly well by the theory, with a consistent set of relevant parameters. However, the tensor which describes the splitting of the Yb ground-state doublet must be modified somewhat from that deduced by Clark et al. Below approximately 10 K, when the magnetization was in the [110] or [112] direction, the nuclear relaxation rate was higher than predicted. These anomalies correspond to those observed in ferromagnetic resonance linewidth, which have been attributed to Yb ions on the octahedral lattice sites normally occupied by iron. Anomalously large values of T1−1 were also observed below approximately 4 K in the [111] and [100] directions, and these remain to be accounted for.
Mechanisms of Reversal with Bias Fields, Deduced from Dynamic Magnetization Configuration Photographs of Thin Films
Authors: Kryder M. H. , Humphrey F. B.
Published: February 2004

Flux reversal with a transverse field in Ni–Fe thin films has been studied using a Kerr magnetooptic apparatus which permits 10-nsec exposures to be taken of the dynamic magnetization configuration. Whenever the applied fields just exceed the critical asteroid, noncoherent rotation occurs, and a 50–100 μ wavelength striped configuration appears in the film. Before the stripes form there is a fast relaxation of the ripple as the magnetization rotates coherently to angles greater (5°–20°) than either the critical angle for reversal or the uniform torque minimum. Therefore, previous models of noncoherent rotation based on instabilities in the ripple which were expected to occur before or at the critical asteroid or uniform torque minimum do not explain the observed reversal process. After the stripes form, depending on the magnitude of the applied fields, one of two processes occurs: either (1) the rotation of the magnetization stops until the stripes break up into small nucleated regions or (2) the rotation is slowed by an order of magnitude and the stripes decrease in amplitude until they vanish. With lower pulse fields diffuse boundary propagation occurs. Magnetostatic stray fields from the boundary cause the magnetization in small regions to reverse by noncoherent rotation so that the propagation is predominant in the direction of the stripes.
Spin Relaxation and the Kondo Effect
Authors: Garland J. W. , Bennemann K. H. , Ron A. , Edelstein A. S.
Published: February 2004

The results of a theoretical investigation of the resistivity, susceptibility, and spin relaxation time of a Kondo system is presented. It is found that the Kondo term ρK in the resistivity is proportional to ln [1+T2/(r−2+ω02)], where ω0 is the molecular field acting on the impurity spins. This result is found to be in excellent agreement with experiment. The dependence of θ2=τ−2+ω02 on temperature and on the concentrations of magnetic impurities and of spin-orbit scatterers is discussed. Experiments are proposed to test the ideas set forth and to probe the nature of the Kondo spin polarization cloud.
Toward Simple Powers of T in the Kondo Effect?
Authors: Star W. M. , Boerstoel B. M. , Van Baarle C.
Published: February 2004

Experimental evidence is presented which strongly suggests that simple power laws govern the temperature dependence of ground-state properties of dilute magnetic alloys exhibiting the Kondo effect. The systems Cu–Fe, Au–V, Pd–Cr, and Pt–Cr are discussed to show that in most cases the impurity specific heat ΔC∝T and the temperature-dependent part of the electrical resistivity Δρ∝−T2, provided the concentration of impurities is low enough. If this concentration is increased above some critical value, the temperature dependences become more complicated.
Magnetic Moment Distribution in Dilute Alloys of Nickel in Palladium
Authors: Aldred A. T. , Rainford B. D. , Stringfellow M. W.
Published: February 2004

Measurements have been made at 4.2°K of the elastic diffuse scattering of 4.8 Å neutrons from ferromagnetic Pd(Ni) alloys containing 3.0, 3.4, 4.7, and 6.3 at.% Ni. The magnetic cross sections, measured with scattering vectors ranging from 0.17 to 1.1 Å−1, are all strongly peaked towards the forward direction. The range of polarization of the palladium matrix around a nickel atom deduced from the measurements is independent of nickel concentration up to 4.7 at.% Ni, and is larger than that obtained by Holden and Low1 for dilute Pd(Fe) and Pd(Co) alloys. The cross section per nickel atom extrapolated to the forward direction increases with increasing nickel concentration up to 4.7 at.% Ni, and then drops sharply. For the most dilute alloys the extrapolated forward cross sections are about a factor of 2 less than those calculated from a general expression due to Marshall and Balcar,2 and it is concluded that the effective concentration of aligned polarization distributions is less than the true concentration of nickel atoms. The mean moment of the nickel atom and the matrix polarization per nickel atom were calculated from the measured cross sections and are independent of concentration for the three most dilute alloys, with values of 0.9±0.2 μB and 3.7±1.4 μB respectively.
Temperature Dependence of the Renormalized Exchange Coupling Constant in the Kondo Effect
Authors: Zawadowski A. , Fazekas P.
Published: February 2004

The exchange coupling J is renormalized above the Kondo temperature TK by applying the Abrikosov-Green function method. The renormalized J decreases as TK is approached. The conclusion is drawn that the current theoretical treatments do not contain all the essential contributions, because the many-particle-intermediate states are neglected in the calculation of the scattering amplitude.
Rayleigh Hysteresis Shape: Its Relationship to Displacement Distance of a Single Domain Wall in 50% Ni–Fe
Authors: Woodbury R. C. , Hunt M. R.
Published: February 2004

The need to measure the displacement distance of domain walls from equilibrium for very weak alternating fields (H≪coercive force) in bulk magnetic material has prompted a study of the possible use of the opening of the Rayleigh hysteresis loop to indicate the amount of wall displacement. This paper contains (1) a review of the theoretical relationship between hysteresis shape and the displacement distance of a domain wall, based upon defect-energy models of Rodbell and Bean, and Baldwin; and (2) an experimental approach which provides a measure of the wall displacements versus hysteresis shape for 50% Ni–Fe tape. Discrepancies between the theoretical and measured relationships are noted. In addition, an application is described in which the measured relationship between hysteresis and wall displacement is used to obtain the size of residual domains in 50% nickel-iron.
Grain Boundary Demagnetizing Fields in 3% Si–Fe
Authors: Shilling J. W.
Published: February 2004

Using the Kerr magneto-optic effect, domain structure was observed during dc and 60-Hz magnetization in 3% Si–Fe bi-crystals and commercial samples with (100) [001] grain orientation. High-speed movies were taken at 3600 frames/sec using a stroboscopic light source. A significant influence of grain boundary demagnetizing fields on domain structure was found. Reverse spikes and complex V-line structures were observed which reduced the normal component of magnetization at grain boundaries. These structures did not appear in the demagnetized state and occurred only when the sample was magnetized.
Hall-Effect Domain Detector
Authors: Strauss W. , Smith G. E.
Published: February 2004

Electrical readout of digital information transported by closed domains in magnetically uniaxial platelets requires sensing flux changes of 1–10 pWb emanating from an area 2–25 μm in diameter. Using an n-type epitaxial layer on a p-type silicon substrate we have developed a beam-leaded Hall-effect device suitable for sensing domains in orthoferrites. In these materials the minimal domain diameter is approximately 25 μm and the flux density is typically 0.01 T. Some properties of the Hall-effect detector are: active area ≈400 μm2, active thickness ≈1 μm, input and output resistance ≈1.5 kΩ, rated current Ir=8 mA, and risetime <50 nsec. Over the experimental range |B| ≤0.01 T and I≤Ir, the measured Hall voltage satisfied VH = (S0 - S2I2)IB, where S0≈16 V/A·T and S2≈ 3×104 V/A3·T. In detecting orthoferrite domains were have obtained 0.5 mV signals. We discuss the design and fabrication, the electrical and mechanical characteristics, and the limitations of the device. Improved detector performance is possible, and guidelines for its realization are given.
Measuring WR and dEK/dψ with an RSM and Integrator
Authors: Flanders P. J.
Published: February 2004

A new method to measure WR and dEK/dψ uses a rotating simple magnetometer induction technique and an electronic integrator. To measure M sinα, the integrated component of the induced signal normal to H, the sample turns at an ω<5 rpm; to measure WR/H the dc component for an ω>10 Hz, M 〈sinα〉Av, is recorded continuously for a single slow sweep through the field. Changes of less than 10−2 emu can be detected in vM sinα, recorded versus ψ, or in vM 〈sinα〉Av, plotted versus H.
Magnon Interactions in Terbium
Authors: Nielsen M. , Mo/ller H. Bjerrum , Mackintosh A. R.
Published: February 2004

Magnon energies and lifetimes have been studied in Tb and Tb-10% Ho single crystals by inelastic neutron scattering. The lifetimes of magnons propagating in the c-direction have been measured in the ferromagnetic phase of Tb, and are found to decrease with increasing temperature and wave-vector, probably principally due to magnon-magnon interactions. The interaction of magnons with phonons has also been observed and the effect of Ho impurities on this interaction studied. In addition, excitations which are ascribed to local modes associated with the Ho ions have been observed. The dependence of the indirect exchange interaction on temperature in the alloy gives information on the mechanisms responsible for the transition from the helical to ferromagnetic structures. The dependence of the magnon energies on magnetic field at low temperatures gives detailed information on the role of magnetoelastic effects in the magnetic anisotropy. It is found that the cylindrically symmetric magnetoelastic effect gives a large contribution to the q=0 magnon energy, in accordance with the ``frozen lattice'' model, and that the hexagonal anisotropy is probably principally due to crystal field effects.
Magnetic and Crystallographic Properties of Pr–Gd Alloys
Authors: Tissot L. , Blaise A.
Published: February 2004

Various Pr–Gd alloys, covering the whole range of compositions, have been studied by x-ray diffraction and static magnetic measurements. The magnetization measurements were made in fields extending to 26 KOe in the temperature range 2°–500°K. For the Pr–Gd system, we find the following phase diagram with the corresponding magnetic properties: (1) a Pr-rich phase of double hexagonal structure which is paramagnetic down to 2°K and which follows the Curie-Weiss Law; (2) A Gd-rich phase of compact hexagonal structure which is ferromagnetic at low temperature; and (3) A phase based on the composition Pr2Gd5 of super hexagonal structure (analogous to the structure of Sm) which is antiferromagnetic at low temperature. Two alloys having compositions just either side of this superhexagonal phase were studied. Their crystallographic structures could not be determined with precision. Their magnetic behavior corresponds to that observed in ferrimagnets. The ferromagnetic Curie temperatures of these alloys are higher than those observed in Gd93Pr7, situated in the Gd-rich phase.
Spin-Wave Dispersion Relation for Gadolinium
Authors: Koehler W. C. , Child H. R. , Nicklow R. M. , Smith H. G. , Moon R. M. , Cable J. W.
Published: February 2004

A large single crystal (23 g) of 99.99% 160Gd has been grown and measurements of the spin-wave dispersion relations in the a-, b-, and c-directions have been carried out at 78°K by means of the coherent inelastic scattering of neutrons. Constant-Q and constant-E modes of operation of the triple axis spectrometer at the HFIR were utilized. Least-squares analyses of the data show that five interplanar constants are required for a satisfactory fit. The constants exhibit both positive and negative signs as expected for a long-range oscillatory interaction. The dispersion curves are similar to those observed for ferromagnetic Tb,1 but have much greater maximum energies. The energy gap at q=0 is unmeasurably small and indicates a relatively small anisotropy energy. In the c-direction, the measured dispersion curve gives directly the Fourier transformed exchange interaction J(0)-J(q). This exhibits no other extreme values except that at the origin. At higher temperatures, the magnitudes of the maximum magnon energies decrease, as expected, and the shape of the curve is modified as well.
Field-Induced Spin Reorientation in ErCrO3
Authors: Holmes L. , Eibschütz M. , Van Uitert L. G.
Published: February 2004

A field-induced spin reorientation has been observed in the weak ferromagnet, ErCrO3, at temperatures below the Néel point, TN=133.2°K. With a magnetic field, H, along the a axis of this orthorhombic compound, the spontaneous magnetization rotates from the c axis, at H=0, to the a axis, at H=Ht. The ``transition'' field, Ht, increases from zero at TN to 11 kOe at T=22°K. The temperature dependence is discussed in terms of a formula which gives the first-order Er3+ contributions to Ht. Above 120°K, the data can be fitted to the curve Ht=a(1-T/TN)1/2, with a=8.1±0.5 kOe. The canting angle for the Cr3+ sublattices and the effective field, Heff, on the Er3+ ions have been estimated from spontaneous-magnetization data. These data were obtained by extrapolating from high magnetic fields to H=0 for both the c and a axes. A canting angle of 35 mrad gives reasonable agreement with both sets of data, but Heff reverses sign on reorientation of the spins. At low temperatures, Heff≈−10 kOe along the c axis.
Magnetically Ordered Perovskites in the System La1−xCaxFe1− xMnxO3
Authors: Banks E. , Tashima N.
Published: February 2004

A series of solid solutions with the general formula La1−xCaxFe1− xMnxO3, where x is from 0.0 to 1.0, have been synthesized and their structural, magnetic and electrical properties have been studied. Polycrystalline samples were prepared by the usual ceramic method, firing at 1350° under a flow of oxygen gas to keep the cations in the desired valence states. X-ray diffraction shows these samples to be orthorhombically distorted perovskites for compositions up to x=0.3 and apparently cubic perovskites from 0.3<x<0.7. Beyond this composition two phases are present. From the measurements of magnetization between liquid-nitrogen and room temperatures, there appeared no evidence of ferromagnetic couplings between cations in the B sites as expected from the Goodenough and Kanamori rules, but they showed very weak residual magnetic moment (around 0.04 μB per formula unit). Mössbauer spectra showed that the iron ions stay in the trivalent state. Chemical analysis shows that at least 97% of the Mn is present as Mn4+. Electrical resistivity and thermo-emf measurements indicate that conduction in these samples apparently occurs by a hopping mechanism.
Anisotropic Magnetic Structures in Spinels
Authors: Boucher B. , Buhl R. , Perrin M.
Published: February 2004

A molecular field theory is developed to find the possible configurations of magnetic moments for cubic and tetragonally distorted spinels in the presence of anisotropy. The starting assumptions are, in a normal spinel both A and B ions are magnetic, A-B interactions are predominant and anisotropic, A moments are ferromagnetically ordered and have no anisotropy, only B moments have a local anisotropy, the magnetic cells remain either fcc for the cubic spinels or bcc for the tetragonal spinels. For one B ion the Hamiltonian is H=-μBHA [G]S-μBH0 [g]S, where HA is the field created by A moments, H0 is the external field, and [G] and [g] are tensors representing exchange and local anisotropy, respectively, and are taken to have the symmetry of the surrounding oxygen octahedron. By minimizing the energy of the whole system and taking into consideration the symmetry of the cell, we find at T=0 and H0=0 a general solution corresponding to a nonregular configuration of B moments. This configuration itself depends on its direction in crystal space, which in turn is defined by the choice of parameters. The resulting A and B moments are generally noncollinear. Some particular cases that correspond to earlier experimental data for spinel manganites are described. The deformations of one structure under the influence of an external field are also given.
Rare-Earth Sublattice Canting in DyIG, ErIG, and YbIG
Authors: Pickart S. J. , Alperin H. A. , Clark A. E.
Published: February 2004

Neutron diffraction data taken on DyIG, ErIG, and YbIG at show superlattice reflections at low temperatures that indicate a decomposition of the rare-earth sublattice. The data are interpreted with a model in which rare-earth spins tilt away from [111] in {110} planes, with a double conical arrangement, although this model is not unique.
Adiabatic Magnetization Cooling in Ytterbium and Gadolinium Iron Garnets
Authors: Clark A. E. , Alben R. S.
Published: February 2004

We have observed large adiabatic magnetization cooling (≈6°K) in ytterbium iron garnet (YbIG) and dilute gadolinium iron garnet in the 3°–30°K temperature range. In samples of YbIG diluted with yttrium, reductions in temperature up to 10°K were observed. In pure YbIG, isentropic curves taken near the compensation point outline a magnetic phase boundary in the H-T plane at which the cooling suddenly ceases. The boundary extends from the compensation point (≈8°K) at H=0 to above 17°K for H=110 kOe. The high-temperature phase is characterized by a collinear sublattice configuration with the rare earth antiparallel to the field and thus possesses a large negative magnetocaloric effect (−0.1°K/kOe). Isentropes and magnetization curves were calculated for YbIG in the molecular field approximation using an iterative method to find the lowest-energy configuration of the iron sublattice and the six rare-earth sublattices. Depending upon the direction of the field, several phase transitions arise from the competing influences of anisotropy, exchange, and Zeeman energies. Some transitions are first order and others are second order.
Role of the Ytterbium Spins in the Spin Reorientation in YbFeO3
Authors: Aring K. B. , Sievers A. J.
Published: February 2004

The spin-reorientation transition in YbFeO3 is explained by including the rare earth-iron exchange interaction in a spin-wave model, without resorting to a temperature-dependent iron anisotropy. In a four-sublattice model (2 Fe and 2 RE) the iron spins are coupled to each other and to the RE spins by both symmetric and antisymmetric exchange. There are four modes at k=0. Two of these modes reduce to those of the iron-only model in the absence of the RE spins. Another mode has the frequency of a single RE spin in the exchange field of the iron sublattices. The fourth mode goes to zero frequency when the Fe-RE interaction cancels the iron anisotropy, resulting in a spin-reorientation transition. Measurements of far-infrared absorption spectra of YbFeO3 have been made and confirm many aspects of the model. The similarities between the spin-reorientation transitions in different orthoferrites suggest that a similar model may be valid for all.
New Approach to the Theory of Itinerant Electron Ferromagnets with Local-Moment Characteristics
Authors: Evenson W. E. , Schrieffer J. R. , Wang S. Q.
Published: February 2004

The understanding of ferromagnets, like iron, which exhibit localized moment behavior above the Curie point yet show itinerancy has long stood as a major theoretical problem. An account will be given of recent progress on this problem which was achieved through functional integral methods. This technique transforms the interacting electron system into an average over a system of noninteracting electrons moving in a Gaussian-weighted external ``magnetic'' field which acts only on the electronic spins. For a single magnetic impurity in a free electron metal, a single approximation allows one to go from Pauli paramagnetism to localized moment behavior in a smooth manner as the atomic exchange interaction is increased. The two impurity problem leads to an effective exchange coupling as in the Heisenberg model, which is antiferromagnetic for the nondegenerate orbital case studied here. Application of the technique to homogeneous systems leads to damped spin waves in the ferromagnet in lowest approximation.
Photoinduced Uniaxial Magnetic Anisotropy and Optical Dichroism in Silicon-Doped Yttrium Iron Garnet [YIG(Si)]
Authors: Dillon J. F. , Gyorgy E. M. , Remeika J. P.
Published: February 2004

Photoinduced magnetic anisotropy and optical dichroism have been studied in silicon-doped YIG at cryogenic temperatures. These effects belong to a new class of magneto-optical effects in which the overlap properties of the excited states of ions on different sites are important. The spectral variation of the photoinduced dichroism shows the position of the operative Fe+ + state to be at about 10 000 cm−1. Photoinduced torque studies are interpreted to indicate that a large fraction of the Fe+ + ions may be moved among various sets of inequivalent sites on irradiation by intense white light.
Energy Bands, Stoner Modes, and Spin Waves in Iron
Authors: Thompson E. D. , Mook H. A.
Published: February 2004

Using the energy bands of iron as calculated by Wakoh and Yamashita, we calculated the density of Stoner excitations along the three principal-axis directions. The spin-wave dispersion curves are then calculated in the RPA approximation using intraatomic and interatomic exchange. For the rigid-band spin splitting necessary for the correct Bohr magneton number, the calculated dispersion curves display negative energies for small wave vectors for zero interatomic exchange and yield the experimental magnon mass for an interatomic exchange of 0.016 eV. Inelastic neutron scattering measurements using the triple-axis technique on iron (3% silicon) at room temperature indicate an almost isotropic magnon dispersion curve with a small quartic term and an intersection of the magnon disperson curve with the Stoner continuum at an energy of 90 meV and at a wave vector of 0.65 Å−1.
Anisotropic g Factors of Nickel, Palladium, and Platinum
Authors: Mueller F. M. , Freeman A. J. , Koelling D. D.
Published: February 2004

The effective g factors of states on all sheets of the Fermi surface for fcc paramagnetic nickel, palladium and platinum have been considered. Calculations have been carried out using both the combined interpolation scheme and the Symmetrized Relativistic Augmented Plane Wave (SRAPW) methods. Corrections due to the outside of the muffin-tin spheres potential (included for Pd and Pt) are shown to be small. Strong spin quenching in all three systems is caused by combination of the close proximity of the dominant X5 and L3 (single group representation) levels to the Fermi energy and the raising of their degeneracies by the important spin-orbit interaction. Comparisons with the experimental data, in particular static susceptibility and dHvA orbital g factors, are presented.
g Factor and Exchange Splitting in Pure Pd and Pt and Cobalt-Doped Pd
Authors: Windmiller L. R. , Ketterson J. B. , Hörnfeldt S.
Published: February 2004

The anisotropy of the g factor on all sheets of the Fermi surface of pure Pt and Pd has been investigated by studying the spin splitting amplitude vanishing of the de Haas-van Alphen effect. In all cases the g factor was observed to be anisotropic and varied by as much as 25% from its free space value of 2. Thus, estimates of the Stoner enhancement factor deduced from the calculated density of states with a g factor of 2 may be in considerable error. Evidence for the itinerant nature of the ferromagnetism in cobalt-doped palladium has been observed both from the disappearance of the expected spin splitting zeros and the beating of the frequencies derived from corresponding cross-sectional areas on the exchange split bands. An estimate of the magnitude of the exchange splitting is made from the beat frequency.
Magnetic Properties of the Pseudobinary Alloys Au4(Mn1−xCrx)
Authors: Yessik M. , Noakes J. , Sato H.
Published: February 2004

An investigation by means of electrical resistivity, magnetization, and magnetic-susceptibility measurements has been made on a series of pseudobinary alloys intermediate between ferromagnetic Au4Mn and antiferromagnetic Au4Cr having the general form Au4(Mn1−xCrx). The magnetic transition points as determined by both ferromagnetic and paramagnetic measurements vary markedly with composition and have a minimum near x=0.6. All the samples up to at last x=0.8 exhibit ferromagnetic behavior with the ferromagnetic moment passing through a minimum near x=0.6. However, the paramagnetic moments vary linearly with composition. A model based on an antiferromagnetic interaction between Mn and Cr moments is proposed.
Optical Study of Ordering in DyPO4, DyAsO4, and DyVO4
Authors: Wright John C. , Moos H. W.
Published: February 2004

Photoelectric optical spectroscopy has proven to be of great value in studying the magnetic behavior of the isostructural crystals DyPO4, DyAsO4, and DyVO4. At high resolution absorption lines of these crystals exhibit a five line sub-structure resulting from various combinations of four thermally flipped nearest-neighbor moments. The relative intensities of each line are directly proportional to the number of ions having a given near-neighbor moment configuration. Ordering temperatures for the three crystals have been accurately determined by measuring the relative intensities and determining the point at which there is a sudden change in the short-range order. Zeeman studies of the three crystals indicate DyAsO4 and DyVO4 are quite different from DyPO4. The moments in DyPO4 are constrained along the c-axis producing a three dimensional Ising system. On the other hand, the moments of DyAsO4 and DyVO4 are in a plane perpendicular to the c-axis. Discontinuities occur in the Zeeman splittings when the antiferromagnetic order is destroyed.
Conductivity of Magnetic Metals
Authors: Erskine J. L. , Stern E. A.
Published: February 2004

A Boltzmann equation appropriate for magnetic conductors is presented. The new element in this equation that distinguishes it from the normal case is the contribution from the spatial polarization of the electron wave functions introduced by the spin-orbit coupling. From this Boltzmann equation the wave number and frequency-dependent conductivity σ(q, ω) is calculated for the two limiting cases where the relaxation time is infinite: (a) q=0 in the presence of a uniform magnetic induction B, and (b) B=0 but q is nonzero. Case (a) is relevant to understanding magneto-optic effects, and case (b) is relevant to understanding the surface impedance in the extreme anomalous skin region (EASR).