bluuebunny/crossref_metadata_2025 huggingface dataset:
A study of cooling rates during metallic glass formation in a hammer and anvil apparatus
Authors: Kroeger D. M. , Coghlan W. A. , Easton D. S. , Koch C. C. , Scarbrough J. O.
Published: February 2003

A model is presented of the simultaneous spreading and cooling of the liquid drop in a hammer and anvil apparatus for rapid quenching of liquid metals. The viscosity of the melt is permitted to vary with temperature, and to avoid mathematical complications which would be associated with spatial variation of the viscosity, Newtonian cooling is assumed. From an expression for the force required to spread the specimen, coupled equations for the mechanical energy balance for the system and the heat transfer from the sample to the hearth and hammer were obtained, and solved numerically. The sample reaches its final thickness when the force required to deform it becomes greater than the force exerted on it by the decelerating hammer. The model was fit to measurements of sample thickness versus hammer speed, using the interface heat transfer coefficient, h, as an adjustable parameter. The values of h so obtained vary somewhat with the melt alloy/substrate metal combination. From predicted cooling curves, the effects of hammer speed, sample size, and initial melt temperature on the cooling rate and the efficiency of glass formation can be assessed. Addition of sample superheat shifts the cooling curve relative to the expected position of the time-temperature-transformation curve for formation of crystalline material from the melt, and thus is an effective means of increasing the probability of glass formation in this type of apparatus.
Scanning electron microscope charge-collection images of grain boundaries
Authors: Marek Jiri
Published: February 2003

Images of grain boundaries obtained in the scanning electron microscope operated in the electron beam-induced current mode are calculated. Images of boundaries in semicrystalline silicon solar cells are measured in the experiment and agree within 2% with theory. The calculated profiles depend strongly on the diffusion length of the semiconductor, providing a new method for determining the diffusion length of the material.
Diffusion of gallium in quartz and bulk-fused silica
Authors: Mizutani Shuzo , Ohdomari Iwao , Miyazawa Takeo , Iwamori Toshimichi , Kimura Itsuro , Yoneda Kenji
Published: February 2003

Diffusion of Ga into quartz (crystal SiO2) and bulk-fused silica (amorphous SiO2) was studied by neutron activation analysis. Slow and fast diffusion of Ga was observed in bulk-fused silica, while in quartz only slow diffusion was observed. The difference in the diffusion mechanisms is discussed on the basis of the difference in porosity of the two materials. In the bulk-fused silica, which has a lower density of 2.20 g cm−3, there are two regions with high and low densities. The higher density region is composed of cristobalite, which has the maximum distance between atomic strings of (at most) 6 Å. The lower density region is composed of a random network of Si and O atoms, and in the network there exist many microchannels, an average diameter and the real density of which are estimated to be 17 Å and 7.5×1011 cm−2, respectively. These microchannels act as the high-speed diffusion paths, while the cristobalite region is the slow diffusion path. In quartz which has a density of 2.65 g cm−3, the widest interatomic spacing perpendicular to c axis is about 5 Å and only the slow (bulk) diffusion can occur. The discrepancy in the diffusion coefficients of Ga reported previously by Grove and Wagner can be explained by the present model.
Electrical and optical properties of reactively sputtered tungsten oxide films
Authors: Miyake K. , Kaneko H. , Teramoto Y.
Published: February 2003

Electrical and optical properties of reactively sputtered tungsten oxide films have been investigated in relation to the oxygen concentration in sputtering atmosphere. The films with 5200–6600 Å thick were prepared under a constant pressure of 5×10−3 Torr using a mixture of Ar and 4–50% O2. Electrical resistivity and spectral transmittance of the films formed depend extremely on the oxygen concentration in the atmosphere. The films formed in an atmosphere containing less than 13% O2 are semiconductive, have a resistivity of 10−3–103 Ω cm, and are blue colored. The films formed in an atmosphere containing more than 16% O2 are transparent and have a resistivity of 107–1011 Ω cm. Optical band gap of the films formed under a sputtering atmosphere containing 8–50% O2 is almost constant and ranges 3.00–3.03 eV. The carrier concentration and Hall mobility of semiconductive films and the refractive index of insulating films were also measured. The presence of a critical oxygen concentration for the formation of either semiconductive or insulating films has been suggested.
Titanium and nickel silicide formation after Q-switched laser and multiscanning electron beam irradiation
Authors: Bentini G. G. , Servidori M. , Cohen C. , Nipoti R. , Drigo A. V.
Published: February 2003

The use of Q-switched ruby laser and multiscanning electron-beam annealing to produce the reaction of thin Ti and Ni films deposited onto silicon single crystals has been studied. Rutherford Backscattering (RBS), 16O(d, p)17O* nuclear reaction, scanning electron microscopy (SEM) observation, and x-ray diffraction were used to characterize the reacted layers. It was found that laser annealing produces a reaction only at the metal-semiconductor interface: the reacted layers are not uniform in composition and more similar to a mixture than to a well-defined phase. On the contrary, the silicide layers produced by multiscanning e beam result from the solid-state reaction of the whole metal film and have a layered structure with well-defined phase composition and sharp interfaces both between the silicide phases and the underlying semiconductor in Ti/Si system. It was observed that the TiSi2 growth mechanism during e irradiation cannot be explained with the parabolic ’’diffusion controlled’’ mechanism operating in the standard furnace annealing. All our observation seems to indicate that the growth mechanism is a ’’nucleation controlled’’ process, in which the growth speed of the disilicide is limited by the speed of ejection of oxygen from a TiSi2 layer. In a Ni/Si system, only the NiSi phase could be obtained as a very uniform layer after the e-beam irradiation; the impossibility of obtaining the Ni2Si phase indicates that, in these conditions, the ’’first-phase nucleation law’’ is no more valid.
Cross diffusion of Cd and Zn in Cu2S formed on ZnxCd1−xS thin films
Authors: Burton L. C. , Uppal P. N. , Dwight D. W.
Published: February 2003

Cadmium and zinc compositions in Cu2S formed on ZnxCd1−xS films (0<x≲0.25) by means of ion exchange have been measured using Auger Electron Spectroscopy (AES), Atomic Absorption Spectroscopy (AAS), and Electron Spectroscopy for Chemical Analysis (ESCA). Net concentrations of Cd and Zn in as-formed Cu2S are generally in the 1018–1019 cm−3 range. Heat treatments in both oxidizing and reducing ambients raise the concentrations by over an order of magnitude, with the Zn concentrations increasing more so than those of Cd. Large increases in Zn at or near the Cu2S surface were measured subsequent to heat treatment, accompanied by increased oxygen. Following heat treatments, Cd and Zn concentrations in the Cu2S ’’bulk’’ are found to be less than 1019 and 1020 cm−3, respectively, for all substrate compositions used.
Measurement of minority carrier capture cross sections and application to gold and platinum in silicon
Authors: Brotherton S. D. , Bradley P.
Published: February 2003

Two techniques have been examined for the direct measurement of minority carrier capture cross sections of deep-lying impurity states in silicon. Both involved the use of a bipolar transistor structure with which minority carrier flow through the device could be controlled. In one technique the carrier capture transient due to the flow of this minority current was directly monitored, and in the other case the current was simply used to empty centers in the minority carrier half of the band gap of majority carriers prior to employing the conventional diode short-circuit technique. It was shown by the former technique that the capture cross sections of gold and platinum in silicon are strongly field dependent. In addition, some evidence is presented to suggest that the donor and acceptor levels of platinum in silicon may not be different charge states of the same center. Data are reported on the temperature dependence of the minority carrier cross sections of gold and platinum in silicon. Lifetime measurements in gold-killed diodes were found to be within a factor of two of the lifetime values calculated using the measured capture cross sections.
Formation of shallow silicide contacts of high Schottky barrier on Si: Alloying Pd and Pt with W versus alloying Pd and Pt with Si
Authors: Eizenberg M. , Tu K. N.
Published: February 2003

The contact reaction of a Si substrate with codeposited Pd-W and Pt-W alloy films has been compared to that with codeposited Pd-Si and Pt-Si alloy films. Effects of alloy composition and heat treatment on component redistribution, reaction product, temperature of silicide formation, and morphological changes have been analyzed by ion backscattering, x-ray diffraction, and scanning electron microscopy and correlated with earlier current-voltage measurements of change of Schottky barrier height. The advantage and disadvantage of using alloys of near noble and refractory metals and of using alloys of near noble metal and Si for the formation of shallow contacts of high Schottky barrier height (0.87–0.74 eV) are reviewed.
Abstract: First-order transitions in the magnetization of single crystal Fe films
Authors: Hathaway K. , Prinz G. A.
Published: February 2003

The magnetization curves of single crystal Fe films exhibit discontinuities as a function of applied field, for particular field directions, indicative of first-order phase transitions. M-H phase diagrams of cubic ferromagnets like Fe with three easy axes are predicted to show a variety of phase transition and multicritical points. They are of special interest in the region H ∥ [111] where the three-state Potts model should apply. Single crystal films were obtained by epitaxial growth on GaAs.1 These films are oriented (11̄0) surfaces containing easy [100], hard [111], and intermediate [110] cubic axes. The restricted geometry of the films does not change the mean field phase diagram for field orientations in the (11̄0) plane between [001] and [111]. However, for in-plane field orientations between [111] and [110] demagnetizing effects prevent the moment from being stabilized along the nearest easy axis by small fields and produce first-order phase transitions not seen in the three-dimensional phase diagram. In particular, the maximum discontinuity and the minimum applied critical field are predicted to occur along [110]. The data are consistent with mean field predictions except that the onset of the first-order discontinuities does not occur until the field is rotated somewhat beyond [111] toward [100]. This modification is obtained by the introduction of an additional anisotropy in the plane of roughly the same order of magnitude as the fourth-order cubic anisotropy. The required magnitude is consistent with the magnetoelastic energy from growth induced strain. A complete account of this work is published elsewhere.2      1 G. A. Prinz and J. J. Krebs, Appl. Phys. Lett. 39, 397 (1981).  2 K. B. Hathaway and G. A. Prinz, Phys. Rev. Lett. (in press).
Monte Carlo renormalization-group studies of critical phenomena
Authors: Swendsen Robert H.
Published: February 2003

Monte Carlo renormalization-group (MCRG) methods are described and illustrated for models of current interest. The calculation of critical exponents and the determination of critical temperatures are discussed, as well as the application to multicritical points.
Critical neutron scattering in the cerium monopnictides
Authors: Hälg B. , Furrer A. , Hälg W. , Vogt O.
Published: February 2003

Diffuse critical neutron scattering has been observed in the cerium monopnictides CeBi, CeSb, and CeAs above the antiferromagnetic ordering temperatures. No transverse fluctuations have been observed in these compounds. The longitudinal spin correlations are anisotropic: For CeBi and CeSb the magnetic interaction within the ferromagnetic sheets is stronger than the interplanar coupling, whereas CeAs shows stronger interaction between the ferromagnetic sheets than within them. For CeSb the long-range ordering below TN has type A2/3 structure with superlattice peaks at q0 = (2π/a)(0,0,2/3), but the fluctuations above TN are of type I antiferromagnetic structure and disappear when the long-range ordering occurs. The ’’frustration’’ in deciding between type A2/3 or type I antiferromagnetic spin arrangement indicates that the first-order phase transition in CeSb is in the vicinity of a Lifshitz point.
Site magnetization of cubic and hexagonal HoMn2
Authors: Hardman K. , Rhyne J. J. , Malik S. , Wallace W. E.
Published: February 2003

Magnetic neutron diffraction profile refinement methods have been used to determine the Ho and Mn site magnetizations in both the cubic C15 and hexagonal C14 Laves phases of HoMn2. The results are correlated with measurements of the temperature dependence of the bulk magnetization, which gave a Tc for both phases of 26 K and overall saturation magnetizations of 6.4μB for the cubic phase and 6.7μB for the hexagonal phase, as extrapolated from field data up to 20 kOe at 4 K. Individual sublattice moments obtained by profile refinement were, for the cubic phase, a Ho moment of 8.1μB, reduced from the free ion value of 10μB by crystal field effects, and a Mn moment of 0.84μB coupled antiferromagnetically, giving an overall magnetization in agreement with the magnetometer results. In the hexagonal phase, the Ho moment was 9.4μB and the two Mn moments were −0.64μB and −1.03μB. The overall magnetization of 7.5μB was higher than that found from the magnetization studies, which were affected by the large uniaxial anisotropy on the Ho site.
Computer simulated bubble memory longevity experiments
Authors: Closson A. , Seitchik J. A. , Hsu J. H.
Published: February 2003

A technique for simulating bubble memory longevity experiments is described. The simulation approach is based on comparing the calculated probability of a data error to a pseudorandom number. Both the exponential model and the normal distribution function model of longevity curve behavior are investigated. A theoretical analysis of the exponential model exists, and our simulated results are in agreement with its predictions. The variances of the longevity slope distribution for the normal function model and for the exponential model are found to be the same. It has been possible to find functions which provide a good fit to the simulated results for the normal function model. A simple procedure is presented for comparing the error rates predicted by the two models, and a table of corresponding error rates is presented.
Mass renormalization in praseodymium
Authors: White R. M. , Fulde P.
Published: February 2003

It is shown that the magnetic excitons in praseodymium metal produce a large and magnetic field dependent effective mass correction and also contribute a T3 term to the specific heat.
Abstract: Exchange interactions in Cs3Cr2Cl9: Inelastic neutron scattering studies
Authors: Stebler A. , Güdel H. U. , Furrer A. , Kjems J.
Published: February 2003

Inelastic neutron scattering (INS) has proved to be a powerful technique for the study of clusters of paramagnetic transition-metal ions.1 Compounds of the type A3M2X9 (A = Rb, Cs; M = Ti, Cr; X = Cl, Br) crystallize in the hexagonal system and contain discrete dimeric clusters of M3+.2 The magnetic and optical-spectroscopic properties of Cs3Cr2Cl9 have been interpreted in terms of noninteracting Cr2Cl93− dimers.3,4 Evidence for interdimer exchange, in addition to the dominant antiferromagnetic intradimer coupling, down to 1.8 K is provided by INS experiments. Splitting of ’’dimer transitions’’ is observed as well as energy dispersion along (001) and deviations of the observed wave-vector-dependent intensities from those calculated for molecular dimer excitations. In contrast to bulk techniques INS provides an ideal means to study the interplay of intra- and interdimer exchange. Compounds of the type A3M2X9 serve as well defined model systems for condensed magnetic materials as well as for spin glasses.      1A. Furrer and H. U. Güdel, J. Magn. Magn. Mater. 14, 256 (1979).  2G. J. Wessel and D. J. W. Ijdo, Acta Crystallogr. 10, 466 (1957).  3O. Kahn and B. Briat, Chem. Phys. Lett. 32, 376 (1975).  4B. Briat, M. F. Russel, J. C. Rivoal, J. P. Chapelle, and O. Kahn, Mol. Phys. 34, 1357 (1977).
Probing magnetism of alloys and intermetallic compounds by spin polarized photoemission (invited)
Authors: Landolt M. , Niedermann Ph. , Mauri D. , Meier F. , Zürcher P.
Published: February 2003

The potential of spin polarized photoemission for studies of alloys and intermetallic compounds is described, specifically with respect to its surface sensitivity. We present studies on well defined Ni1−xFex (100) surfaces for x = 0.2 and 0.6. We find that the majority spin band in the bulk is not full for x = 0.6. We discuss this result in comparison with modern theories of ferromagnetic alloys. The effect of the surface, on the other hand, is strong as soon as surface segregation or adsorbate induced decomposition occurs. Paramagnetic FeTi and ferrimagnetic ErFe2 have been studied. In FeTi we observe oxygen induced precipitation of superparamagnetic Fe particles and ErFe2 was found to exhibit a hydrogen induced surface reaction.
Aspects of transition-metal magnetism
Authors: Williams A. R. , Moruzzi V. L. , Gelatt C. D. , Kübler J. , Schwarz K.
Published: February 2003

The following questions are considered: How do itinerant d electrons of the Heusler alloys produce magnetic moments that are completely localized on the Mn atoms? What is the microscopic origin of Invar anomalies? Why is elemental antiferromagnetism confined to Cr, Mn, and Fe? Why do the Fe atoms in Fe3Si carry two distinctly different magnetic moments? Can we use our understanding of transiton-metal magnetism to ’’design’’ new magnetic compounds composed of nonmagnetic elements? Our answers to these questions are based on the local-spin-density theory of electronic exchange and correlation, implemented using parameter-free self-consistent energy-band calculations.
Are VPd3 and NbPd3 itinerant ferromagnets?
Authors: Burmester W. L. , Sellmyer D. J.
Published: February 2003

Low-field magnetic susceptibility and high-field magnetization results are reported for polycrystalline samples of NbPd3, VPd3, and iron doped VPd3. Recent self-consistent, spin-polarized band calculations have predicted that the pure compounds are itinerant ferromagnets. Down to 1.6 K there is no evidence for either magnetic ordering or exchange enhancement in VPd3 and NbPd3. The Fe-doped alloys exhibit transitions at low temperatures to a magnetic cluster-glass state.
Spin-waves in nickel, iron, and yttrium-iron garnet
Authors: Pauthenet R.
Published: February 2003

The magnetostatic properties of single crystals of nickel, iron, and yttrium-iron garnet have been measured along the three crystallographic axes, in magnetic fields up to 180 000 Oe and at different temperatures between 4.21 and 286 K. The relative accuracy is 0.01%. It is found that the magnetization values as a function of the internal magnetic field satisfy the Holtstein-Primakoff test. A method to determine the spontaneous magnetization is given. The magnetization curves are interpreted in terms of the spin-wave theory; a superimposed susceptibility is determined for nickel and iron.
Magnetic correlations in disordered MncZn1−cTe alloys
Authors: Holden T. M. , Dolling G. , Sears V. F. , Furdyna J. F. , Giriat W.
Published: February 2003

The spin correlations between Mn ions in disordered MncZn1−cTe alloys (c = 0.68, 0.594, and 0.376) have been measured as a function of temperature and concentration by neutron diffraction. The scattering peaks principally around the wave vector corresponding to the (1,1/2,0) reflection, which is the ordering wave vector of the type III antiferromagnetic structure. The magnetic intensity was analyzed in terms of the correlations between a central spin and successive shells of neighbors and these were found to follow the sign sequence for the type III antiferromagnet but with progressively smaller amplitudes. At no temperature or concentration was long range order observed. However, the width of the (1,1/2,0) peak at low temperatures is consistent with a power law and the critical concentration for magnetic ordering is just outside the present concentration range.
Two magnetic subsystems in bimetallic [Co(C5H5NO6)][COCl4]
Authors: Lambrecht A. , Burriel R. , Carlin Richard L. , Mennenga G. , Bartolome J. , de Jongh L. J.
Published: February 2003

The specific heat and susceptibility of the title compound and of [Co(C5H5NO)6][ZnCl4], which are isostructural and monoclinic, have been measured. Two magnetic subsystems are present in the Co/Co compound, the Co2+ ions on octahedral positions exhibiting antiferromagnetic ordering at Tc = 0.95(1) K, the Co2+ ions on tetrahedral positions remaining paramagnetic down to at least 0.04 K. The paramagnetic ions experience two different molecular fields from the ordered Co2+ ions.
Kosterlitz-Thouless transition in two-dimensional planar ferromagnet K2CuF4 (invited)
Authors: Hirakawa K.
Published: February 2003

We report that in 2D planar ferromagnet K2CuF4 the Kosterlitz-Thouless transition occurs in a slightly modified form by the weak 3D interaction. K2CuF4 is a good 2D ferromagnet, but by no means a true XY magnet, the anisotropic part of interaction being only 1%. Nevertheless, it is approximated by a good 2D XY magnet at low temperatures. We have carried out static magnetization as well as neutron scattering measurements and found that all the critical parameters δ(T), χ(T), κ(T), ξ(T) and η(T) determined in the 2D XY-like crossover regime are in good agreement with the Kosterlitz theory and the Monte Carlo simulation. The existence of the universal jump in Jeff is also indicated through the diffuse scattering measurements.
The exchange splitting of phonon assisted microwave transmission at 9.5 GHz
Authors: Heinrich B. , Cochran J. F. , Myrtle K.
Published: February 2003

We have studied the transmission of 9-GHz microwave power through Ni single crystals cut in the (110) plane with the applied magnetic field along the [100] direction. Our studies were carried out in the FMR field region. The transmission of microwave power was observed to be greatly enhanced by the propagation of ultrasonic waves generated at the front surface of the sample by magnetoelastic coupling. The observed transmission peak has an envelope whose shape is similar to the FMR absorption line but which has a sharp dip at the field corresponding to the magnon-phonon dispersion curve crossover for the applied frequency ω.
Abstract: Neutron diffraction study of the magnetic structures of HoB4
Authors: Koehler W. C. , Mook H. A. , Fisk Z. , Maple M. B.
Published: February 2003

Magnetic susceptibility, specific heat, and resistivity measurements by Fisk et al. have revealed two ordering transitions in HoB4 at temperatures near 7.1 and 5.7 K. Moreover, the macroscopic measurements indicate that the higher temperature transition is of second order, the lower one of first order. Neutron diffraction measurements on polycrystalline and on single crystal specimens have confirmed these results. The magnetic scattering data have so far resisted a complete interpretation; the following conclusions can, however, be drawn. The magnetic structure in the high temperature phase has a strong oscillatory component, the wave vector of which is equal to (±0.021,±0.021, 0.425) in units of the reciprocal lattice vectors. The magnetic moments are parallel, in sheets normal to the tetragonal c-axis, to one of the four equivalent [100] reciprocal lattice directions. In the low-temperature phase there is a large component of the moments arranged in the simple colinear structure that has been reported for ErB4 and DyB4 by W. Schafer et al. In both temperature ranges there are additional, unexplained, magnetically scattered intensities. The magnetic phase diagram has been studied in applied fields up to 6.4 T and at temperatures down to 1.8 K. Polarization analysis and classical polarized beam techniques have been applied to the single crystals in selected field and temperature ranges.
Abstract: Quadrupolar interactions and structural instabilities in PrAg1−xCux
Authors: Gotaas J. A. , Kouvel J. S. , Brun T. O. , Cable J. W.
Published: February 2003

In order to elucidate the unusually strong quadrupole-quadrupole interactions discovered earlier in PrAg, magnetic and neutron diffraction studies are being made of the pseudobinary compounds PrAg1−xCux. For PrAg0.75Cu0.25, which, like PrAg, has a cubic CsCl-type structure, analysis of high-field magnetization data above the antiferromagnetic Néel point (TN∼9 K) shows that the effective biquadratic (quadrupolar) coupling is about twice as strong as in PrAg, whereas the average bilinear exchange coupling is slightly weaker. PrAg0.5Cu0.5, which has a CsCl-type structure at room temperature, was found to transform to an orthorhombic FeB-type structure (similar to that of PrCu) when it is cooled below ∼150 K. Detailed comparison of the two structures of PrAg0.5Cu0.5 indicates that the instability of the CsCl-type structure probably stems from the softening of certain zone-boundary phonons, which presumably grows as x increases towards 0.5. Such phonons would account for strong effective quadrupolar interactions of negative (antiferro) sign, precisely of the type seen in PrAg and PrAg0.75 Cu0.25.      a) Work supported by NSF Grant No. DMR 78-12777.  b) Work supported by the U.S Department of Energy.  c) Work sponsored by the U. S. Department of Energy under contract W-7405-eng-26 with the Union Carbide Corp.  1 T. O. Brun, J. S. Kouvel, and G. H. Lander, Phys. Rev. B 13, 5007 (1976).
Coqblin-Schrieffer interaction and magnetic orderings and excitations for cerium and light actinide monopnictides and monochalcogenides
Authors: Yang David , Cooper Bernard R.
Published: February 2003

The anisotropic Coqblin-Schrieffer (CS) interaction between the Ce3+ ions, which arises from the hybridization of the localized 4f and the conduction electrons, is shown to give the overall magnetic ordering behaviors of cerium and light actinide monopnictides and monochalcogenides. With equal nearest neighbor and next nearest neighbor CS interactions, the near saturation colinear orderings observed in cerium monopnictides are stabilized; while for dominant nearest neighbor CS interaction, the canted ferromagnetic or 2k antiferromagnetic orderings, and the 3k ordering in the presence of the cubic crystal field, as observed in the uranium monopnictides are found to be stable. The excitation spectra in the colinear and 2k structures are strongly anisotropic, while in 3k ordering, the dispersion is nearly isotropic.
A spin glass with finite range interactions: More diseases
Authors: Bowman D. R. , Levin K.
Published: February 2003

We set up and solve the Bethe approximation for a spin glass with finite range interactions. We obtain the finite z analogue of the Thouless Anderson Palmer equations and the free energy functional at all T. In the configuration averaged theory, the entropy S(T) and all other properties are well behaved on a Cayley tree. For real lattices S(0) = 0, but the specific heat is negative near T = 0 for all but small values of z.
Model of magnetic behavior of dilute FePd alloys
Authors: Medina R. , Parra R. E.
Published: February 2003

A model has been developed that describes well several magnetic properties of FePd alloys with concentrations 0.025<c<0.5 at.% Fe. We obtained an expression for the exchange energy among the clusters that surround the Fe atom and an interaction of Heisenberg type between the clusters. Using the Monte Carlo method for a classical Heisenberg system we estimated the critical temperatures for the onset of ferromagnetism and a good agreement was obtained with the experimental data at different concentrations. We conclude that the onset of ferromagnetism at concentrations greater than 0.025 at.% Fe in FePd is due to the dimensions of the magnetic clusters.
The Bethe Ansatz in magnetism: An introduction (invited)
Authors: Fowler M.
Published: February 2003

After reviewing the basic ideas of the Bethe Ansatz using the simplest possible model—the one-dimensional interacting boson system of Leib and Liniger—we discuss the magnetic systems for which it has been used successfully. These include spin one-half chains, the Hubbard model, and the Kondo problem.
Point contact spectroscopy of g-values in metals
Authors: d’Ambrumenil N. , White R. M.
Published: February 2003

It has previously been demonstrated that the I-V characteristic associated with current flow through a constriction whose dimension is less than the electron mean free path is nonlinear. The nonlinearity is largely associated with electron-phonon scattering. We have analyzed the case in which the contacts contain localized impurity spins. We show that, in the presence of an applied magnetic field, the inelastic spin-flip, scattering should be readily observable in the I-V characteristic, thereby providing an alternative technique for obtaining g values of localized spins in metals.
Hyperfine field anisotropy of Co in C15 RCo2 compounds (R = rare earth)
Authors: Hirosawa S. , Nakamura Y.
Published: February 2003

Results of 59Co NMR investigation on the C15 type RCo2 compounds (R = rare earth) in the ferro-, ferri-, and paramagnetic states are reviewed. An enormous anisotropy in the 59Co hyperfine fields, which results in antiparallel hyperfine fields at two magnetically inequivalent Co sites in RCo2 compounds with the [111] or [011] easy axis, is attributed to unquenched orbital moment of Co atoms. Analysis of temperature dependence of 59Co Knight shifts reveals the important role of the spin-orbit coupling. Observation of well-resolved satellite lines in Tb1−xYxCo2 yields an estimate of transferred hyperfine fields due to the rare earth spins as +42 kOe in TbCo2 at 4.2 K, where the positive direction is chosen to be the direction of the Co moment. From consideration of the sign and the magnitude of lattice dipole fields, Lorentz fields, and the transferred fields, the fraction of the orbital moment on Co in the RCo2 series is found to vary from 3% in GdCo2 to 26% in PrCo2.
Mössbauer investigation of sputtered ferromagnetic amorphous FexB100−x films
Authors: Blum N. A. , Moorjani K. , Poehler T. O. , Satkiewicz F. G.
Published: February 2003

Iron boride amorphous films were prepared by rf sputtering of polycrystalline FeB and Fe2B powders. The films were analyzed for purity, uniformity, and composition by secondary ion mass spectrometry and were analyzed for lack of long range order by x-ray diffraction. As in the melt quenched alloys, Mössbauer spectra revealed a broad and nearly symmetric distribution of hyperfine fields in samples with a composition near a-Fe2B. The hyperfine field distribution in samples with a composition near a-FeB, however, is asymmetric, and more significantly, reveals a large number of Fe sites with zero magnetic hyperfine field at temperatures down to 10 K. Analysis of the data throws light on the chemical short range order in the alloys.
Speculations on the critical behavior of reduced moment antiferromagnetic cerium compounds (invited)
Authors: Lawrence Jon
Published: February 2003

In certain trivalent cerium compounds, fast spin fluctuations associated with the proximity of the 4f level to the Fermi level completely suppress magnetic order; in others the ground state is antiferromagnetic, but the spin fluctuations show up in thermodynamic and spectroscopic properties. These effects reflect the proximity in parameter space to a zero-temperature magnetic/nonmagnetic transition. The critical behavior associated with this transition falls in the category of ’’quantum critical phenomena’’ and is expected to be quite interesting. This paper discusses the results of recent neutron scattering experiments in CeIn3 in the light of this expected behavior. Key features are nearly-mean-field behavior and strong suppression of the critical fluctuations. Comparisons will be made to the behavior of the more conventional cerium based metamagnet CeAl which we have recently determined, as well as to the behavior of other spin fluctuation magnets, such as CeAl2.
Low-temperature properties of CeAl3
Authors: Flouquet J. , Lasjaunias J. C. , Peyrard J. , Ribault M.
Published: February 2003

Specific heat measurements on CeAl3 are described and compared to thermal-expansion results. At very low temperatures, the Grüneisen parameter reaches giant negative values. Comparisons are made with the properties of 3He and the unstable-valent 4f compounds (YbCuAl, CeBe13, CeSn3, and CePd3). It is suggested that the magnetic anisotropy may play a major role.
Electronic structure of cerium in Ce1−xYxPd3 and Ce1−xMxAl2 (M = Sc, Y)
Authors: Kappler J. P. , Krill G. , Besnus M. J. , Ravet M. F. , Hamdaoui N. , Meyer A.
Published: February 2003

Lattice constant, susceptibility, and electrical resistivity data for Ce1−xYxPd3 system suggest that the IV behavior of the cerium alloys goes over to an integral cerium four-valent state in the Y-rich alloys (xcr∼0.5). However, XPS results for the 3d core level spectra in Ce1−xYxPd3, Ce1−xScxAl2, and Ce1−xYxAl2 show that there is no modification in the XPS spectra when the electronic transition of cerium is achieved.
Crystal field effects in the Van Vleck paramagnet PrBe13: Magnetization, resistivity, and NMR
Authors: Besnus M. J. , Kappler J. P. , Lemius B. , Benakki M. , Meyer A.
Published: February 2003

Measurements of the magnetization, the electrical resistivity, and the NMR relaxation of PrBe13 in the temperature range 1.4–300 K are reported. The results clearly show the effect of the crystal field splitting of the 4f level of the Pr ion and are compared to relevant theories. The proposed crystal field energy level scheme, Γ1−Γ4−Γ3−Γ5, with an overall splitting of 135 K, is consistent with all experimental data.
Abstract: Spin dynamics of trivalent and intermediate-valent TmSe
Authors: Furrer A. , Buhrer W. , Wachter P.
Published: February 2003

By means of inelastic neutron scattering we have measured the dynamical susceptibility of the same TmcSe (c = 0.87, 0.99) single crystals which have previously been used for studying various thermal, magnetic, and transport properties.1,2 The experiments have been performed above and below TN∼3 K. From the excitation spectra observed for trivalent Tm0.87Se we have determined the molecular-field and the crystal-field parameters; the latter drastically deviate from the parameters known for the thulium monopnictides.3 The energy spectra observed for intermediate-valent Tm0.99Se are partly in contrast to the results obtained for polycrystalline material,4 and to recent single-crystal data.5 Below TN there is a single dispersionless excitation at around 1 meV. Above TN the energy spectra can be characterized by a superposition of two quasielastic lines corresponding to slow and fast magnetic relaxation rates which differ almost by an order of magnitude, in agreement with theoretical predictions.6 A detailed description of this work has been published elsewhere.7      1B. Batlogg, H. R. Ott, E. Kaldis, W. Thoni, and P. Wachter, Phys. Rev. B 19, 247 (1979).  2H. Boppart, A. Treindl, P. Wachter, and S. Roth, Solid State Commun. 35, 483 (1980).  3H. L. Davis and H. A. Mook, Magnetism and Magnetic Materials − 1973, AIP Conf. Proc. No. 18, p. 1068.  4M. Loewenhaupt and E. Holland-Moritz, J. Magn. Magn. Mater. 9, 50 (1978).  5B. H. Grier and S. M. Shapiro, Valence Fluctuation in Solids (North-Holland, Amsterdam, 1981), p. 325.  6E. Muller-Hartmann, Electron Correlation and Magnetism in Narrow Band Systems (Springer, Berlin, 1981), p. 128.  7 A. Furrer, W. Buhrer, and P. Wachter, Solid State Commun. (1981).
Muon spin relaxation studies of the spin glass AgMn (invited)
Authors: Heffner R. H. , Leon M. , Schillaci M. E. , MacLaughlin D. E. , Dodds S. A.
Published: February 2003

We report measurements of magnetic ion dynamics in the spin-glass sytem AgMn (1.6 at. %) using the muon spin relaxation technique (μSR). The salient features of the theoretical μSR lineshapes in zero and finite longitudinal applied fields are reviewed. Zero-field measurements below the glass temperature (Tg = 7.6 K) exhibit a static width a(T) which decreases with increasing temperature reminiscent of an ’’order parameter’’ behavior. At T≲Tg/2 the static width is consistent with that calculated for a random orientation of frozen Mn spins. The temperature dependence of a(T) is attributed to rapid, small-amplitude fluctuations of the local field about its quasistatic equilibrium position. An apparent stiffening of the fluctuation frequency spectrum is observed as the applied magnetic field is increased. The measured upper limit for frequencies which significantly relax the muon spin is about 50–100 times smaller than the peak in the mode density calculated by Walstedt and Walker in Monte Carlo simulations of small-amplitude harmonic excitations in CuMn (0.9 at. %), a system similar to ours. Above Tg the spin motion changes dramatically, from small-amplitude fluctuations to nearly complete reorientation, as expected. Measurements in longitudinal fields above Tg confirm the anomalous field-induced static broadening reported in earlier transverse field measurements.
Magnetic ordering in EuxSr1−xS, a diluted Heisenberg system with competing interactions (invited)
Authors: Maletta H.
Published: February 2003

Presence of additional antiferromagnet bonds in a ferromagnet changes magnetic ordering in a dilution series drastically. An ideal system to study these effects is the insulating EuxSr1−xS, based on EUS, the well-known model substance for a Heisenberg ferromagnet. The competition between ferromagnetic nearest neighbor exchange J1 and antiferromagnetic next-nearest neighbor exchange interaction J2 with J2/J1 = −0.5 is shown to cause a breakdown of ferromagnetism in EuxSr1−xS at x = 0.51, far above the percolation threshold xp = 0.13. In the intermediate concentration regime, 0.13⩽x⩽0.51, spin-glass behavior is observed very similar to the features in metallic spin glasses. Results on (Eu, Sr)S provide clear evidence for a cooperative phenomenon at the spin-glass transition, as distinguished from ordinary thermal blocking of superparamagnetic clusters. By increasing the Eu concentration just above xc, long-range ferromagnetic order is found to coexist with a high amount of wrong aligned spins, which again is caused by the competing exchange interactions. Neutron (Bragg and small-angle) scattering demonstrates an interesting change in magnetic order by lowering the temperature. The unique properties of (EU,Sr)S can be compared with realistic numerical model calculations.
An electron spin resonance study of FeyNi80−yP14B6 alloys in the reentrant regime
Authors: Manheimer M. , Bhagat S. M. , Kistler L. M. , Rao K. V.
Published: February 2003

We report susceptibility, hysteresis loop, ESR, and VSM measurements on a few alloys of the series FeyNi80−yG20 and compare them with our earlier studies on FexNi75−xG25 alloys, especially when x = y. In both cases we find a re-entrant regime for intermediate Fe concentrations. Replacement of G by Ni enhances Tc and stiffens the magnetic lattice. Spin freezing is accompanied by the onset of a distribution of internal fields which have a nonzero average for the G20 alloys when y?15.
A mictomagnetic behavior of Cr7Se8
Authors: Kaneko T. , Sugawara J. , Kamigaki K. , Abe S. , Yoshida H.
Published: February 2003

The mictomagnetic property of Cr7Se8 having a monoclinically distorted NiAs-type crystal structure was studied in the magnetic field up to 108 kOe. The susceptibility anomalies are observed at about 30 and 162 K. The former is considered to relate with an origin of a mictomagnetic behavior of this compound. The latter agrees with the Néel point observed by neutron diffraction study. The magnetization curve up to 108 kOe showed an abrupt increase of magnetization at temperatures lower than 70 K, as well as an ordinary spin flip at higher temperatures. From the measurement of the hysteresis loop between ±108 kOe, it can be considered that there is a mictomagnetic behavior, which is related to the local disturbance of ordering of Cr ion vacancies in this compound.
Bulk magnetization of dysprosium-scandium alloys
Authors: Ferrick J. H. , Rhyne J. J. , Segnan R.
Published: February 2003

Bulk magnetization measurements were made on Dy0.25Sc0.75 and Dy0.75Sc0.25 alloys. The Dy0.25Sc0.75 alloy has the characteristics of a spin-glass material. The low-field magnetization exhibits a peak near 27 K when the sample is warmed after cooling in zero applied field. Cooling in the presence of a field destroys the peak and results in a nearly temperature-independent magnetization below the peak ’’spin-freezing’’ temperature. The Dy0.75Sc0.25 alloy undergoes an antiferromagnetic transition at TN = 118 K and remains in a spiral antiferromagnetic state down to below 4.2 K. Ferromagnetic ordering can be induced by an applied field. The critical field for this transition is 13.5 kOe just below TN, increases as temperature decreases in contrast to conventional behavior, and exhibits a sharp anomalous rise below 29 K.
ac susceptibility of intermediate concentration PdMn alloys
Authors: Ho S. C. , Maartense I. , Williams Gwyn
Published: February 2003

We have measured the ac susceptibility and electrical resistivity of a large number of PdMn alloys containing between 0.5 and 10.45 at. % Mn, from which a detailed magnetic phase diagram has been constructed. This phase diagram appears to suggest the possibility of a double transition, i.e., a paramagnetic to ferromagnetic transition followed by a ferromagnetic spin-glass transition at low temperature, for Mn concentrations between 3 and 5 at. %. A detailed analysis of the ac susceptibility of alloys in this concentration range does not support such implied behavior in this system.
Abstract: Spin glass-ferromagnetic transition in disordered Ni-Mn
Authors: Aitken R. G. , Cheung T. D. , Kouvel J. S.
Published: February 2003

The magnetization M of a disordered Ni-Mn alloy of ∼22 at. % Mn was measured as a detailed function of field H and temperature. For the alloy cooled to 4 K in zero H, M increases slowly as H is raised to a critical value (Hc∼200 Oe), where M increases rapidly and then slowly approaches ferromagnetic saturation as H is raised to 5 kOe. As H is subsequently lowered, M undergoes a similarly rapid drop at the same Hc and then slowly reaches zero at zero H. Since the isothermal remanence is zero, the low-M state below Hc cannot derive from simple ferromagnetic domain effects. That this is a spin-glass state is evidenced by field-cooling experiments which result in displaced hysteresis loops at 4 K. At higher temperatures after cooling in zero H, the field-induced transition to ferromagnetism is seen to occur at a progressively lower Hc. Hc reaches zero at ∼40 K, above which the spontaneous M varies like that of a ferromagnet with a Curie point of ∼350 K. However, the low-temperature values of the spontaneous M are well below the values expected from a ferromagnetic alignment of all the atomic moments. Similar experiments on a Ni-Mn alloy of ∼26 at. % Mn reveal it to be a typical spin glass with a susceptibility cusp at ∼80 K.1 A detailed determination of the magnetic phase diagram of the disordered Ni-Mn system is currently in progress.     a) Work supported by NSF Grant. No. DMR78-12777. b) Presently at University of Colorado, Colorado Springs, CO 80907. c) Presently at Queens College-CUNY, Flushing, NY 11367. 1  ESR results for this alloy are reported at this conference by Hurdequint, Kouvel, and Monrod.
M-H loop shift phenomena in torqued magnetostrictive tape cores carrying electric current
Authors: Dalpadado Ranjit N. G.
Published: February 2003

The phenomena of shifting of M-H loops in torqued magnetostrictive tape cores carrying dc electric currents are described. Large loop shifts of the order of the coercive force of the well torqued samples are obtained for relatively small core-currents (e.g., Iz = 106 A/m2 giving less than a 5 °C temperature rise over ambient/Hex = 99 A/m). The shifting of M-H loops is accompanied by a decrease in the coercive force. The shift phenomena, including reduction of coercive force, are described by an unified macroscopic model for the magnetization.
The results of microwave transmission and FMR absorption studies in iron-rich Metglas Fe82B12Si6 at 9, 24, and 73 GHz
Authors: Cochran J. F. , Myrtle K. , Heinrich B.
Published: February 2003

We have carried out microwave measurements on an iron-rich Metglas at 9, 24, and 73 GHz. Two different techniques were used. FMR absorption measurements were made at 9, 24, and 73 GHz which allowed us to study the magnetic properties within a thin surface layer. FMAR transmission measurements at 73 GHz were also made which revealed some of the bulk properties of this material. It was found that the values of magnetic damping obtained from the FMR absorption measurements were significantly different from those obtained by FMAR transmission. We believe this difference is due to the insensitivity of the FMAR transmission measurements to microscopic inhomogeneities. The role of specimen treatment (annealing, polishing) was also investigated.
Kinetics of formation of induced magnetic anisotropy in a zero-magnetostriction amorphous alloy
Authors: Ho Kai-Yuan , Flanders P. J. , Graham C. D.
Published: February 2003

The kinetics of formation of magnetic annealing anisotropy have been measured in the zero-magnetostriction amorphous alloys (Fe0.063Co0.937)75Si15B10 over the temperature range 165–380 °C by analysis of torque curves on single disk samples. Only at temperatures above 330 °C was it possible to reach equilibrium saturated values of the anisotropy in reasonable times (less than 20 h). By assuming that the equilibrium saturated value of the induced anisotropy is linear with temperature, it is possible to deduce an activation energy for the magnetic annealing process in a well-annealed sample. The value is about 2.0±0.1 eV. This is considerably higher than the value of 1.4 eV found by Luborsky or 1.7 eV reported by Chambron and Chamberod for Fe40Ni40P14B6. The higher value in this work is presumably due to the relatively high glass transition temperature and crystallization temperature of the FeCoBSi alloy. The kinetic data reveal the existence of range or relaxation times, which can be analyzed assuming a log-normal distribution. The width of the distribution of relaxation times β decreases with increasing temperature.
Magnetic, Mössbauer, and resistivity studies of amorphous Fe74Zr26 and Fe81Hf19 alloys
Authors: Chien C. L. , Unruh K. M. , Levy A. , Liou S. H. , Stokes J. P. , Gambino R. J. , Fukamichi K.
Published: February 2003

Amorphous metal-metal samples of Fe74Zr26 and Fe81Hf19 have been studied by bulk magnetic, Mössbauer spectroscopy and resistivity measurements. The values of TC have been determined to be 285 K and 295 K for Fe74Zr26 and Fe81Hf19, respectively. Both the magnetic isotherms and Mössbauer measurements indicate that these samples are ferromagnetics. The isomer shifts and the quadrupole interactions are much smaller than those of amorphous Fe-metalloid systems. The P(H) are broad and extend to small H values. Negative temperature coefficients of the resistivity are observed at low temperatures followed by a resistivity minimum at temperatures slightly above room temperature. These results are significantly different from those of amorphous Fe-metalloid systems with comparable Fe contents.