bluuebunny/crossref_metadata_2025 huggingface dataset:
Observation of the dynamic behavior of the antiferromagnetic-ferromagnetic phase transition in the one-dimensional spin-1/2 antiferromagnet α-CuNSal
Authors: Azevedo L. J. , Narath A. , Richards P. M. , Soos Z. G.
Published: February 2003

Proton spin lattice relaxation rates in the spin-1/2 Heisenberg antiferromagnet α-CuNSal have been measured in applied fields up to 125 kOe in the temperature range 1–4 K. All inequivalent protons in the unit cell can be identified. The strong coupling of protons close to the antiferromagnetic (AF) chain provides an opportunity to use 1H spin lattice relaxation rates, T1−1, to probe the dynamics of the spin system through the antiferromagnetic-ferromagnetic (AF-F) phase transition as the critical field, Hc, is exceeded. The AF-F phase transition is observed at Hc=4J/geμB(J/kB=3.04 K) as a strong enhancement of T−11. For fields above Hc, the proton T−11 decreases over 4 orders of magnitude. The effect of increasing temperature is to broaden the peak in T−11, and move it to lower field. The uniform magnetization of the AF spin system, as measured by proton resonance shifts, is in excellent agreement with calculations by Bonner and Fisher. The behavior of the relaxation rate can be understood in terms of the fermion representation.
Magnetic ordering of GdxEr1−xRh4B4 near the superconducting region
Authors: Kohn S. , Wang R. H. , Smith J. L. , Huang C. Y.
Published: February 2003

GdxEr1−xRh4B4 exhibits superconductivity at some critical temperature Tc followed by the onset of long-range ferromagnetic ordering at a lower temperature and a loss of superconductivity for x<xc?0.28, where xc is the critical concentration at which superconductivity is suppressed. For x above xc, the compound is no longer superconducting but is still magnetically ordered. We have made ac resistivity R, ac magnetic susceptibility χ, and dc magnetization measurements on samples with x near xc. For x?0.28, the salient features for the R and χ measurements are: (1) In zero external field a sharp maximum in the ac χ (T) and a minimum in R(T) are observed. With a small external dc magnetic field (∼102 Oe), the extrema in χ (T) and R(T) are depressed and smeared considerably with a corresponding shift in the temperature at which the extrema occur. (2) The sample is not superconducting down to 0.6 K. (3) In the presence of a dc magnetic field, a second ac χ peak appears at a slightly higher temperature. (4) The field dependence of the ac susceptibility resembles that of a spin glass. Details of the field dependence of these observations and the nature of these phenomena will be presented.
Mössbauer and magnetic study of the antiferro to ferrimagnetic phase transition in Fe9S10 and the magnetokinetics of the diffusion of iron atoms during the transition
Authors: Marusak L. A. , Mulay L. N.
Published: February 2003

The antiferromagnetic to ferrimagnetic phase transition referred to as the λ transition in Fe9S10 has been explained by many workers on the basis of a structural change without any experimental evidence. Our Mössbauer and X-ray diffraction results support Lotgering’s suggestion that the ferrimagnetism at about 493 K arises from the 4C superstructure. The antiferromagnetic to ferrimagnetic (λ) phase transition is explained in terms of a vancancy rearrangement. Using absolute reaction rate theory and measurements of magnetization as a function of time at constant temperature around the transition, coefficients of diffusion for iron atoms along the C axis have been determined over the range 440 to 484 K and found to be 10−18 cm2/sec.
The magnetocaloric effect in dysprosium
Authors: Benford S. M.
Published: February 2003

The magnetocaloric effect in polycrystalline Dy was measured between 84 and 280 K in measuring fields from 1 to 7 T. These adiabatic temperature changes reflect structural changes in Dy with applied field and temperature, and include the first magnetocaloric data for a helical antiferromagnet. These measurements were made to evaluate Dy as working material in magnetic refrigeration applications. Above TN (179 K) a field increase always causes heating; below TN fields less than about 2 T cause cooling for some values of initial temperature. The largest temperature increase with a 7 T field occurs at the Neel point (-T=11.5 K), and at fields below 2 T near the Curie point (-T=2 K at 100 K). For refrigeration purposes, the optimal working region for a Dy cooling element is field dependent. This Dy data suggests that, because of complex magnetic structure changes, antiferromagnetic rare earths may be useful for refrigeration over a broad temperature range near TN at very high fields, and may be preferable to ferromagnetic materials over certain restricted temperature regions above the Curie point in low fields produced by permanent magnets (?1 T).
Magnetic interactions in ternary superconductors
Authors: Shenoy G. K. , Dunlap B. D. , Fradin F. Y. , Kimball C. W. , Potzel W. , Pröbst F. , Kalvius G. M.
Published: February 2003

Numerous ternary superconductors containing rare-earth atoms have recently been studied in order to investigate the magnetic interactions between the conduction electrons and local magnetic moments. These investigations range from the evaluation of the strength of spin-flip scattering of the conduction electrons off the rare-earth moments to the problem of the coexistence of superconductivity and magnetic order. We present results of our studies on (Eu,Sn)Mo6S8, ErRh4B4, Er1−xHoxRh4B4 and Er1−xGdxRh4B4 using primarily the Mössbauer effect in 151Eu and 166Er, and nuclear magnetic resonance of 95Mo. The paramagnetic hyperfine spectra of the rare-earth ions indicate a weak coupling of the 4f magnetic moment to the conduction electrons. The enhanced Hc2 value in (Eu,Sn)Mo6S8 is found to be related to a negative s-band polarization at the Mo site. The magnetic moment on the Er atom in ErRh4B4 (and in related materials) in the magnetically ordered state is found to be about 8.3 μB. This is 30% larger than that measured from neutron diffraction studies, indicating that only a component of the moment shows long-range magnetic order.
Transport properties of magnetic amorphous alloys
Authors: Fert A. , Asomoza R.
Published: February 2003

We discuss several aspects of the transport properties of magnetic amorphous alloys : contributions from magnetic ordering and from Kondo effect to the resistivity, resistivity minima of non-magnetic origin, magnetoresistance, resistivity anisotropy, extraordinary Hall effect.
Magnetic, transport, and thermal properties of ferromagnetic EuB6
Authors: Fisk Z. , Johnston D. C. , Cornut B. , von Molnar S. , Oseroff S. , Calvo R.
Published: February 2003

Magnetic measurements on Al-flux grown EuB6 crystals show that this material orders ferromagnetically with a transition temperature Tc=13.7 K. The effective moment derived from paramagnetic susceptibility measurements gives μeff=7.76 μB, and the saturation magnetization extrapolated to 0 K is within 10% of the theoretical value of 7 μB expected for Eu+2. The magnetic order, however, cannot be that of a simple colinear ferromagnet because the magnetic specific heat in zero applied magnetic field shows a broad maximum centered about 9 K rather than the expected λ-like anomaly at 13.7 K. Finally, transport measurements suggest that EuB6 is an intrinsic semimental.
Hall effect and magnetoresistance in Fe1−xCuxCr2S4
Authors: Ando K. , Nishihara Y. , Okuda T. , Tsushima T.
Published: February 2003

The Hall effect and the magnetoresistance effect are studied in Fe1−xCuxCr2S4. FeCr2S4 is a ferrimagnetic semiconductor and CuCr2S4 is a ferromagnetic metal. The number and the mobility of charge carriers are determined independently. The mobility decreases as the temperature increases toward the Curie temperature. This shows that the anomalous increase in the electrical resistivity around the Curie temperature is caused by the decrease in the mobility by the spin-disorder scattering. The temperature dependence of the number of charge carriers indicates that this system is still in a semiconductor state at x=0.65. The negative magnetoresistance effect is observed below the Curie temperature, and is discussed in terms of the spin-disorder scattering. The compositional dependences of the magnetoresistance effect and the Curie temperature suggest the semiconductive-to-metallic transition near x=0.85.
New evidence for a narrow conduction band in CdCr2Se4
Authors: Coutinho-Filho M. D. , Balberg I.
Published: February 2003

We report a study of the critical behavior of the resistivity in n-type (In-doped) and p-type (Ag-doped) CdCr2Se4 single crystals. The results are analyzed in terms of the various proposed band models. We conclude that the valence band is a wide band with a small exchange interaction between the carrier and the localized spins. The conduction band is a narrow band, the broadening of which yields the enhancement of the mobility in the ferromagnetic region.
Abstract: Equivalence of large biquadratic exchange to small uniaxial single ion anisotropy
Authors: Hunter P. E. , Libelo L. F. , Tanaka T.
Published: February 2003

For an S=1 Heisenberg ferromagnet, including uniaxial single ion anisotropy rather than biquadratic exchange leads to the same ordering instability behavior. (AIP)
Two-dimensional XY magnets with annealed non-magnetic impurities
Authors: Berker A. N. , Nelson David R.
Published: February 2003

The global phase diagram of a vectorial generalization of the Blume-Emery-Griffiths model is obtained using Migdal’s approximate renormalization procedure. Classical two-component spins and non-magnetic impurities populate a triangular lattice, with nearest-neighbor interactions. The phase diagram in thermodynamic field space is divided into magnetic and impurity-rich phases by a first-order surface of discontinuous impurity concentrations, terminating in an Ising-type critical line. The magnetic region is further divided into a high-temperature paramagnetic phase and a low-temperature Kosterlitz-Thouless phase. The exponent η=1/4 of the pure system is preserved at the higher-order surface separating these two phases. This surface terminates in a line of critical end-points on the first-order surface, and, consequently, no tricritical point occurs for any values of the model parameters. However, the Ising critical line and the line of critical end-points approach each other in a certain limit, yielding an effective tricritical phase diagram. Within the Kosterlitz-Thouless phase, lines of constant η bunch together as the effective tricritical point is approached, in apparent agreement with tricritical scaling. This is also a model for superfluidity and phase separation in helium films.
Nonuniversality in magnetic tricriticality
Authors: Fisher Michael E. , Sarbach Stéphane
Published: February 2003

Magnetic tricritical behavior has been studied on the basis of the recent exact solution [1,2] for the asymptotic tricritical equation of state of the n-component spin model in the spherical model limit n→∞. In d=3 dimensions scaling behavior with classical tricritical exponents is found. However, the scaling functions are nonuniversal, being parametrized by a single variable, z, which vanishes (leaving mean field theory) only when the range, R0, of the exchange interactions becomes infinite. The theory predicts relations between various experimentally accessible ratios of tricritical amplitudes; the ratios vanish identically in mean field theory but are nonuniversal for interactions of finite range. Comparisons with data from magnetization experiments on DAG and FeC12 display unambiguous nonuniversal departures from mean field theory and verify the predicted relations with surprising precision.
Susceptibility calculations for alternating antiferromagnetic chains
Authors: Bonner J. C. , Blöte H. W. J. , Bray J. W. , Jacobs I. S.
Published: February 2003

Earlier work of Duffy and Barr consisting of exact calculations on alternating antiferromagnetic Heisenberg spin-1/2 chains is extended to longer chains of up to 12 spins, and subsequent extrapolations of thermodynamic properties, particularly the susceptibility, are extended to the weak alternation region close to the uniform limit. This is the region of interest in connection with the recent experimental discovery of spin-Peierls systems. The extrapolated susceptibility curves are compared with corresponding curves calculated from the model of Bulaevskii, which has been used extensively in approximate theoretical treatments of a variety of phenomena. Qualitative agreement is observed in the uniform limit and persists for all degrees of alternation, but quantitative differences of about 10% are present over the whole range, including the isolated dimer limit. Potential application of the new susceptibility calculations to experiment is discussed.
Abstract: Spin wave theory in lower dimensional systems: Failure of the dynamic scaling hypothesis in the ferromagnetic chain
Authors: Reiter G.
Published: February 2003

A classical spin wave theory is shown to be capable of calculating averages of rotationally invariant quantities for classical systems without long range order but with a diverging coherence length at T=0. One imagines that one is calculating a conditional average, in which one spin has a given direction, and then expands the spin operators in small deviations transverse to this direction, and since for a rotationally invariant quantity, the conditional average is equal to the full average, the results do not depend upon the choice of axis. (AIP)
Review of measurements of critical exponent beta in simple magnetic systems
Authors: Suter Robert M. , Hohenemser Christoph
Published: February 2003

A critical review is given of measurements of the critical exponent β in three dimensional magnetic systems. Many claims of discrepancies between experimental data sets and between experiments and theory are either corrected or are found to be groundless on the basis of our reanalysis. A large percentage of the experiments are found to lie too far from the critical point to allow deduction of exponent values with uncertainties smaller than the differences between model calculation predictions. Those data which do allow deduction of exponent values appear to show a slight deviation from recent theoretical calculations.
Field dependent magnetic behavior in CsNiF3
Authors: Griffin J. A. , Folkins J. , Ferre J. , Regis M. , Royce B. S. H.
Published: February 2003

CsNiF3 is a transparent magnetic insulator in which Ni2+ ions form one dimensional chains parallel to the hexagonal c axis. One dimensional short range ferromagnetic order is observed down to TN=2.61 K below which three dimensional easy plane antiferromagnetic order occurs. We present measurements of the wavelength, temperature, and magnetic field dependence of the magnetic linear dichroism in CsNiF3. This dichroism is shown to be a sensitive probe of the field dependent magnetic order.
Random spin system in the Bethe-Peierls-Weiss approximation
Authors: Shukla Prabodh , Schowalter Leo J. , Klein Michael W.
Published: February 2003

We examine the thermodynamic properties of a set of Ising spins interacting via various random potentials Jij in a modified Bethe-Peierls-Weiss (BPW) approximation and obtain the spin glass order parameter, the internal energy and the specific heat. When the effective number of neighbors z→∞, we show that the magnetic properties of the system are identical in the (i) BPW-method, (ii) the selfconsistent mean-random-field (MRF) method, and (iii) the Sherrington-Kirkpatrick derivation. The entropy at T=0 is still negative and our method suggests how including correlations would result in a more physically correct solution as T→0. We also obtain the phase diagram as a function of z in the MRF-method from z=2 to z=20 and find that for z≳8 the phase diagram differs little from the z=∞ case. Similarly, we obtain the thermodynamic properties of the random spins with an RKKY potential in the BPW method. We find that for low concentrations the method gives a discontinuous slope in the magnetic susceptibility χ and the specific heat CM at the spin-glass transition temperature Tg, however the maximum in CM and χ occur well below Tg.
Abstract: Numerical studies of the low temperature behavior of a three dimensional planar model of a classical spin glass
Authors: Huber D. L. , Ching W. Y. , Fibich M.
Published: February 2003

Calculations of the ground state properties and low lying excitations in a three dimensional planar model of a classical spin glass are presented. (AIP)
Anomalous temperature dependence associated with conduction electron scattering from isolated Cr impurities in Pd and Pt
Authors: Roshko R. M. , Williams Gwyn
Published: February 2003

The electrical resistivity of several dilute PtCr and PdCr alloys, containing between 0.05 and 0.3 at % Cr, has been measured from 1.4 to 300 K. The incremental resistivity Δp (T) appears to contain two contributions; the first arises from conventional Matthiessen’s Rule deviations, while the second contribution decreased monotonically with increasing temperature. With the conventional DMR assumed to be temperature-independent above about 60 K, it was found that the temperature dependence of the incremental resistivity Δρ (T≳60 K) in both systems was well represented by an expression of the form Δρ (T) =Ac+Bc ln (T2+T2)1/2. The single impurity characteristic temperature Ts was found to be concentration-independent in both systems with a value of Ts?45 K for PdCr and ?75 K for PtCr. The difference between the experimental values for Δρ (T) and the predicted form for Δρ (T) extended to low temperatures allowed a determination of the conventional DMR. The latter have been fitted to a ’’dirty limit’’ empirical model and are in good agreement with those deduced from previous measurements on nonmagnetic impurities in Pd and Pt. The latter result lends support to our assumption regarding the behaviour of the conventional DMR at high temperatures.
Pressure dependence of antiferromagnetic ordering in γ-Fe and type 310 stainless steela)
Authors: Liu C. M. , Ingalls R.
Published: February 2003

We report the effect of high pressure on the 57Fe Mössbauer effect of ∼60 Å γ-Fe precipitates in copper, as well as in type 310 stainless steel. Using the Mössbauer thermal scan technique at various pressures we find Néel temperatures in both systems to decrease with pressure presumably as expected in a weak itinerant model. The variation of the isomer shift with pressure is also described.
Abstract: Magnetic incoherent elastic scattering of neutrons from an antiferromagnetic CrFe alloy
Authors: Fawcett E. , Holden T. M.
Published: February 2003

In order to determine the perturbation of magnetic moment density around a single iron impurity, we have attempted to measure the magnetic incoherent elastic scattering of neutrons from a Cr 2.8 at.% Fe single crystal (TN=257±2 K) in the antiferromagnetic phase at 96 K. (AIP)
FMR measurement of anisotropy dispersion in amorphous GdFe films
Authors: Soohoo R. F. , Morrish A. H.
Published: February 2003

Ferromagnetic resonance spectra of a series of evaporated Gd1−xFex amorphous bubble films with x ranging from 67.6 to 81.6 at.% have been measured. From these spectra the g-factor geff was calculated. The experimentally determined values of geff agree well with those expected from Wangness formula. Of particular interest is the comparison of the anisotropy field values HK measured by ferromagnetic resonance and by a vibrating sample magnetometer. Whereas FMR can provide information on the anisotropy distribution in the film, VSM yields at best an average value for HK. In our experiments, several resonance peaks are in general found for a given film indicating the existence of a number of regions having different values of Hk′=HK−4πM. Interface effects on the substrate side and oxidation at the air-film interface may result in layers of different chemical composition.
Stress induced anisotropy in amorphous Gd-Fe and Tb-Fe sputtered films
Authors: Takagi H. , Tsunashima S. , Uchiyama S. , Fujii T.
Published: February 2003

The perpendicular anisotropy caused by the internal planar stress due to the substrate constraint in Gd-Fe and Tb-Fe sputtered films was investigated. The internal planar stress σ in these films is found to be very sensitive to preparation conditions, especially to the argon pressure during sputtering, PAr. Stress is compressive for low PAr and tensile for high PAr. The contribution of the stress to the total perpendicular anisotropy varies depending on PAr. Measurement of the anisotropy change before and after the removal of the substrate reveals that the predominant part of the perpendicular anisotropy originates from the internal stress due to the substrate constraint for Tb-Fe films with a composition of around 30 at.%Tb, where the magnetostriction is extraordinarily large.
Electrical resistivity of glassy (FexNi100−x)80B20 (x=30, 40, 50, 60, 70) alloys at elevated temperatures
Authors: New D. A. , Arajs Sigurds , Luborsky F. E. , Kemény T. , Vincze I.
Published: February 2003

Electrical resistivity (ρ) of glassy (FexNi100−x)80B20 (x=30, 40, 50, 60, 70) has been studied as a function of temperature (T) between 300 and 1000 K using heating rates of ∼2.5 K/min. The slopes of the ρ vs T curves are positive for all the alloys in their glassy state. At the crystallization temperature the quantity ρ abruptly decreases. This decrease increases rapidly with the Fe content. No anomalies in the ρ vs T curves are observed at the corresponding Curie temperatures. For the sample containing 40 at.%Fe, ρ ∼ T between 300 and 600 K. All other samples show considerable deviations from this relationship. The quantity dρ/dT at 400 K increases with increasing ρ at 400 K for alloys with x = 40, 50, 60, and 70. The crystallization temperatures determined from the ρ vs T plots are in good agreement with values obtained by other techniques. A few comments are made on the nature of crystallization processes in this system.
Spin flop in a one-dimensional Heisenberg antiferromagnet(a)
Authors: Stahlbush R. E. , Scott J. C.
Published: February 2003

We have measured, using an a.c. susceptometer, the field and temperature dependence of the magnetic response of a polymer containing chains of antiferromagnetically coupled chromium ions of ground term 4A2g. The temperature dependence of the initial susceptibility indicates an exchange strength J=5.0 K. Below about 10 K, a smeared spin-flop transition is observed centered at a field of 20 kG. The single ion anisotropy parameter, D, is thus 0.04 K. The magnitude of the spin-flop field and the temperature below which the magnetic anisotropy exists can be reconciled in terms of a model of ordered one-dimensional domains, separated by domain walls whose excitation energy and length are determined by J and D.
Temperature dependence of the magnetostriction and magnetization in single crystal HoFe2
Authors: Abbundi R. , Clark A. E. , Koon N. C.
Published: February 2003

The magnetostriction (λ100) and the magnetic moment of single crystal HoFe2 were measured as a function of temperature down to T=4.2 K. HoFe2 forms a cubic (C15) Laves phase compound with the easy axis of magnetization along the [100] crystallographic direction. At room temperature the magnetostriction is rather small with λ100=−67×10−6 and λ111=200×10−6. λ100 increases substantially with decreasing temperature reaching a value of −745×10−6 at T=4.2 K. This behavior is contrary to that observed in DyFe2 (also [100] easy) where λ111≫λ100. The decrease in λ100 with increasing temperature was found to be much more rapid than could be explained by lowest order single-ion magnetoelastic theory. On the other hand, magnetostriction measurements of λ111 over the temperature range 275–325 K result in a temperature dependence which can satisfactorily be explained by the single-ion model. The spontaneous magnetic moment at T=0 K is 134.5 emu/g. Taking the the gJ value of 10 μb for the Ho3+ sublattice moment results in an Fe moment of 1.67 μb. This value is nearly equal to those previously obtained in other RFe2 compounds. The magnetization curves at room temperature along the principal crystallographic directions yield anisotropy constants K1=5.5×106 erg/cm3 and K2=6.4×106 erg/cm3.
Towards a uniform magnetic phase diagram for magnetic alloys with mixed types of order
Authors: Nieuwenhuys G. J. , Verbeek B. H. , Mydosh J. A.
Published: February 2003

Many experimental and theoretical investigations have separately characterized the magnetic properties of spin glasses and random ferromagnetic alloys. Magnetic systems which are on the borderline between the two ordering mechanisms show a double magnetic transition as a function of temperature. Two distinct phases have been found in AlFe, CrFe, AuFe, PdMn, etc. In this paper we will review the experimental properties of these systems and compare their behavior with the results of existing theories. The close analogy between the systems and the good agreement with the theoretical calculations suggest that a general magnetic phase diagram exists which can be applied to many random magnetic alloys with competing ferro- and antiferromagnetic interactions.
Fluctuation effects in spin glasses
Authors: Young A. P.
Published: February 2003

This talk reviews recent work on the theory of spin glasses. The Edwards-Anderson approximation is explained and shown to be invalid even as a mean field theory because it predicts a certain positive definite correlation function to be negative. A method of restoring stability by breaking ’replica symmetry’ due to Bray and Moore is then discussed and shown to imply an infinite number of symmetry breakings in the ordered phase. Estimates of the ’lower critical dimension’ are reviewed. Several independent methods predict a value of four which, if correct, would imply that experiments have to be interpreted in terms of gradual freezing rather than a sharp phase transition. Finally we argue that the replica method gives correct results and previous difficulties arise from choosing an incorrect solution of the equations.
A cluster model of spin glasses: Towards reconciling theory and experiment
Authors: Levin K. , Soukoulis C. M. , Grest G. S.
Published: February 2003

We have proposed a cluster mean field theory of the spin glasses in which dynamical clusters of spins are the fundamental entity. We review experimental evidence for spin clusters and show that within our model it is possible to understand (i) why the specific heat and resistivity have a broad maximum at temperatures above TSG at which the magnetic susceptibility cusp appears and (ii) why the total neutron cross section dσ/dΩk has a k-dependent maximum at temperatures below TSG, where k is the momentum transfer to the neutron. These results suggest that there may, in fact, be a sharp transition to the spin glass phase, which turns out to be more apparent in susceptibility than in specific heat, resistivity, and neutron measurements.
Temperature dependence of magnetization of amorphous Fe-B-C alloys
Authors: Hatta S. , Egami T.
Published: February 2003

Temperature and magnetic field dependence of amorphous Fe-B-C alloys obtained by splat cooling were measured and compared with those of Fe-B alloys. It was found that the effect of replacing boron by carbon in Fe86B14 alloy was to change significantly the temperature dependence of magnetization in the direction of increasing spin-wave stiffness, and to reduce the saturation susceptibility. The high value of room temperature saturation induction found in Fe-B-C alloy is therefore attributed to a change in the temperature dependence of magnetization, rather than to change in the magnetic moment at 0 K.
Power loss measurements in amorphous alloys
Authors: Blundell M. , Overshott K. J. , Graham C. D.
Published: February 2003

A method for measuring magnetic losses in amorphous alloys is described.It is based on the use of a lock-in amplifier to determine the magnitude and phase of the fundamental component of magnetic field H when the induction B is forced to vary sinusoidally with time. The method is applicable to very small samples in the form of straight lengths or of toroids, and gives satisfactory results at flux levels approaching saturation if the flux wave form can be held sinusoidal. Data are presented on several amorphous alloy compositions as a function of peak induction and of frequency. Annealing effects have been investigated.
Soft magnetic properties of metallic glasses—recent developments
Authors: Hasegawa R. , O’Handley R. C.
Published: February 2003

Two major aspects of the soft magnetic properties of metallic glasses, i.e., high magnetic permeability and high saturation induction, are discussed. Recent development in the area of high permeability materials is centered around the zero-magnetostriction Co-rich metallic glasses having Si and B as metalloids. The heat treated materials studied thus far show low-field magnetic properties comparable or superior to those of commercial supermalloy. A typical example includes an effective permeability at l kHz exceeding 50,000. Attractive high saturation induction metallic glasses are found in the series Fe82B18−xSix. Typical dc results for field-annealed samples of this glass with x=8 are Hc=0.03 Oe, Br=12 kG and μ (20) =8,000. Core loss under sine flux conditions at 60 Hz is 0.24 watts/kg at 16 kG. This value is nearly five times lower than that of the widely used power transformer material grade M-4 Si/Fe (1.3 watts/kg) and well below that of Fe-B glass. The stability against crystallization of Fe82B10Si8 is higher than that of Fe80B20.
Superconductivity and electronic properties of amorphous transition metal alloys
Authors: Johnson W. L.
Published: February 2003

Amorphous superconducting materials were first prepared over twenty years ago by Buckel and Hilsch [1] using the technique of evaporation onto a cryogenically cooled substrate. Since this early work on simple metals, such studies have been extended to transition metal thin films and more recently to bulk metallic glasses prepared by rapid cooling of liquid metals. This article presents a brief survey of current experimental work on amorphous transition metals and alloys. The relationship between superconductivity and microscopic electronic structure is emphasized. Results of structural studies, magnetic susceptibility and specific heat measurements, photoemission spectroscopy, transport measurements, and superconductive tunneling experiments are covered. The role of structural disorder in determining the nature of the superconducting state is discussed, and possible technical applications of these materials which exploit their unique properties are pointed out.
Structure of magnetic amorphous alloys studied by energy dispersive X-ray diffraction
Authors: Egami T.
Published: February 2003

Recent advances in the technique of energy dispersive X-ray diffraction (EDXD) have made it possible to study the atomic structure of amorphous solids with greater accuracy. This paper reviews the techniques involved in the successful utilization of the EDXD method. Also the structural relaxation of amorphous alloys which was recently clearly resolved by the EDXD technique is discussed, as well as the structure of the Fe-B-C amorphous alloys, which were found to have the highest room-temperature saturation induction among the Fe based amorphous alloys.
Abstract: Some fundamental aspects of itinerant amorphous ferromagnetism
Authors: Wohlfarth E. P.
Published: February 2003

Various properties of amophous ferromagnetic materials containing transition metal and metalloid atoms are reviewed. These point clearly to an itinerant electron model description of the materials. (AIP)
Magnetization and Hall effect in amorphous alloys containing Mn
Authors: McGuire T. R. , Taylor R. C.
Published: February 2003

This study of amorphous Gd-Mn, Y-Mn and their ternary alloys with Co prepared as films by co-evaporation indicates that, (a) the Mn moment is compositionally dependent going from ?2μB to 0.5μB per Mn with increased Mn concentration in the alloy, (b) Gd-Mn and Gd- (CoMn) order with antiparallel Gd and Mn moments or (CoMn) moments while Y-Mn samples remain paramagnetic, (c) Curie temperatures are relatively constant with composition which we have interpreted in terms of the Mn-Mn exchange interaction, and (d) the spontaneous Hall effect for Mn as given by ρH/ρ (Hall resistivity/sample resistivity) is about −0.01 per μB of Mn which is opposite in sign to Fe or Co.
Evidence for an impurity like relaxation mechanism in oxygen contaminated amorphous YCo3 films
Authors: Suran G. , Prasad Shiva , Jouve H. , Meyer R.
Published: February 2003

Amorphous YCo3 films are contaminated by oxygen along a thin surface layer when exposed to air at room temperature. The field for resonance corresponding to this surface layer presents a dynamical shift with a well defined minimum. On the other hand linewidth presents a large maximum ΔHmax as a function of temperature. After annealing in vacuum ΔHmax decreases and the dynamical shift is no more detected. The results obtained on a 500 Å thick sample are analysed quantitatively using formulas developed for the longitudinal relaxation mechanism. It is found that the results on both as deposited and vacuum annealed samples are well explained if we assume that the percentage of Co atoms in the ionic state is reduced to about one third of its value after the vacuum annealing.
Magnetoelastic effects in Fe71Co9B20 glassy ribbons
Authors: Mitchell M. A. , Cullen J. R. , Abbundi R. , Clark A. , Savage H.
Published: February 2003

Measurements of the magnetomechanical coupling constant, k, and the ΔE effect have been made on Fe71Co9B20 glassy ribbons quenched by a centrifugal spinning method. An X-ray check of the ribbons showed no trace of crystallinity. The maximum k and ΔE effect were 0.81 and more than 2.2, respectively, obtained after a field anneal of 20 kOe parallel to the width of the ribbon at 384±5°C for 15 min. This relative change in modulus is the largest known.
Fe ion dose dependence of deep levels in Si p+-n junction
Authors: Kumagai Osamu , Kaneko Kunio
Published: February 2003

A peak of deep level transient spectroscopy (DLTS) spectrum obtained from a silicon p+-n junction implanted with iron was investigated and it was found that the energy level and the capture cross section of the trap varied with the iron dose. This is due to a change, with dose, of the concentration ratio of two kinds of traps, a process induced (E3:Ec−0.50 eV) and an iron-associated center (E2:Ec−0.58 eV), which have nearly the same emission rate and give only a single peak to the DLTS spectrum. The concentration of the E2 trap depended on the iron dose, while that of the E3 trap did not.
Optoelectronic switching in a stub transmission line
Authors: Buck J. A. , Li K. K. , Whinnery J. R.
Published: February 2003

We have demonstrated optoelectronic switching in a pulse-forming microstrip line, which utilizes the energy in a laser pulse for triggering. Electrical pulses 1 ns in width and of 1–2 V in amplitude were produced using a 10-ns dye laser pulse of 1-kW amplitude. The possibilities of further pulse shortening appear very promising.
Modeling of a submicrometer gate field-effect transistor including effects of nonstationary electron dynamics
Authors: Carnez B. , Cappy A. , Kaszynski A. , Constant E. , Salmer G.
Published: February 2003

A simple self-consistent model is described, which takes into account nonstationary electron-dynamic effects and gate-edge effects in submicrometer gate FET devices. Analytical formulations are used to describe nonstationary electron dynamics, which are derived by fitting steady-state results of Monte Carlo calculations. The first results show a significant improvement in the transconductance gm as well as in the cutoff frequency for submicrometer devices. A first attempt to optimize the impurity concentration level is made which shows that a compromise can be found for present-day feasible submicrometer gate devices.
Infrared-active phonons in cubic zinc sulfide
Authors: Klein Claude A. , Donadio Robert N.
Published: February 2003

We take advantage of the availability of chemically vapor-deposited zinc sulfide for the purpose of investigating the infrared absorption spectrum of cubic ZnS, at room temperature, and extend the range of currently available measurements into the three-phonon regime. A critical-point analysis of two-phonon events yields a set of accurate zone-edge mode frequencies; they are shown to be consistent with second-order Raman spectral characteristics. The gross features of the three-phonon absorption edge are described in terms of four characteristic frequencies (LO=330, TO=295, LA=193, TA=89 cm−1) and attributed to optical-branch overtones.
Comment on ’’Correlation between process-induced in-plane distortion and wafer bowing in silicon’’
Authors: Gegenwarth Richard E.
Published: February 2003

The paper by L. D. Yau incorrectly reports and discusses results reported by Gegenwarth and Laming [SPIE. J. 100, 66 (1977)]. The observed in-plane distortions in that paper were similar in magnitude to those found by Yau. Most of the data in three different types of experiments showed in-plane distortion in the range of 1/8 to 3/8 μm.
Frequency spectrum of laser-generated ultrasonic waves
Authors: Viertl J. R. M.
Published: February 2003

The frequency spectrum of laser-generated ultrasound has been measured from 5 to 60 MHz. Diffraction corrections are applied to account for spherical wave spreading from the laser-ultrasonic source and the transducer response to spherical waves. The deconvolution applied to obtain the frequency spectrum is described. The spectral shape found agrees qualitatively with a theoretical model for stress wave generation in a laser heated liquid.
On the linearized gradient approximation for diffusion-limited growth of a spherical precipitate
Authors: Enomoto M. , Aaronson H. I.
Published: February 2003

An error in a published [J. Appl. Phys. 41, 4404 (1970)] linearized-gradient analysis of the diffusion-limited growth of a spherical precipitate is corrected. Comparison of the present and previous analyses as a function of supersaturation shows that the numerical effects of the error are small enough to warrant use of the incorrect but simpler analysis unless a high level of accuracy is required.
Magnetic and transport properties of pure and carbon-doped divalent RE hexaboride single crystals
Authors: Tarascon J. M. , Etourneau J. , Dordor P. , Hagenmuller P. , Kasaya M. , Coey J. M. D.
Published: February 2003

Single crystals of pure and carbon-substituted divalent hexaborides EuB6 and YbB6 have been prepared by the Al flux method. Lattice parameters, density measurements, and microprobe analysis show that the single crystals are very close to stoichiometry. EuB6 is ferromagnetic (TC=12.5 K and ϑp=15 K) whileYbB6 is diamagnetic. Resistivity and Hall effect measurements carried out over a wide temperature range show that both pure hexaborides are semiconductors with a small intrinsic gap. The carbon-substituted hexaborides RE B6−xCx (RE=Eu, Yb) have a metallic behavior due to the donation of electrons to the conduction band by carbon atoms. Metallic conduction, at low temperature, in the ’’pure’’ hexaborides is attributed to the formation of an impurity band containing more than 1018 electrons per cm3.
X-ray diffraction study of interdiffusion and growth in (GaAs)n(AlAs)m multilayers
Authors: Fleming R. M. , McWhan D. B. , Gossard A. C. , Wiegmann W. , Logan R. A.
Published: February 2003

A detailed study has been made of interdiffusion in (GaAs)n(AlAs)m multilayer structures grown by molecular beam epitaxy. The subscripts n and m indicate that the structure is a repeating sequence of n monolayers of GaAs followed by m monolayers of AlAs. The time dependence of the Fourier components of the composition modulation at a constant annealing temperature was obtained by measuring the intensities of the superlattice satellites by x-ray diffraction. For a sample with (n,m) = (12,9) at a temperature of 860 °C, the data can be fit by a composition-dependent diffusion coefficient of the form D (C) =8.8×10−20 exp(αC) cm2/sec, where α=2.06 and C is the gallium concentration. The parameter α is proportional to the difference in the diffusion activation energy in GaAs and AlAs. An α of 2.06 at 860 °C corresponds to an energy difference of 0.201 eV. Calculations which assume vacancy diffusion via the arsenic sublattice give an energy difference of 0.25 eV in reasonable agreement with the experimental value. The average diffusion constant for a sample with (n,m) = (1.1,1.1) is 5.3×10−21 cm2/sec at T=800 °C. These results are in good agreement with those reported in the literature. In addition, a large growth anisotropy is observed in the (100) plane with a larger correlation length in the direction parallel to the dangling bonds on the As-rich surface of GaAs.
Mössbauer study of the NiFe2O4 precipitation process from a silicate glass
Authors: Komatsu T. , Soga N.
Published: February 2003

Mössbauer effect measurements were made to study the NiFe2O4 precipitation process from the silicate glass of 50 SiO2–30Na2O–10NiO–10Fe2O3 composition. Both the isomer shift and quadrupole splitting parameters were found to decrease in the NiFe2O4 precipitation process. These decreases were interpreted on the basis of decrease in Fe3+-O2− distance and distortion of Fe3+ ion sites, respectively. The precipitated NiFe2O4 particles of 160 Å showed a stable ferrimagnetic behavior at 300 K, while those of 128 Å exhibited superparamagnetism.
Nonradiative lifetime measurements in time-domain photoacoustic spectroscopy of condensed phases
Authors: Mandelis A. , Royce B. S. H.
Published: February 2003

A theoretical model is presented for the time-domain photoacoustic response of a condensed sample with a two-level optical-absorption band. The nonradiative lifetime of the excited state and the transfer function of the pressure transducer are included in the formalism. The limitations of the technique for nonradiative lifetime measurements are discussed and the experimental conditions necessary for optimum relaxation time determinations are evaluated. It is found that the limitations imposed by the modified gas thermal transport equations used in the model restrict it to relaxation times greater than ∼10−5 sec. This is of the same order as the limit imposed on experimental measurements by the transfer function of commercial microphones.
Extension of the Rosencwaig-Gersho photoacoustic spectroscopy theory to include effects of a sample coating
Authors: Fernelius Nils C.
Published: February 2003

The Rosencwaig-Gersho theory for the photoacoustic signal from a homogeneous solid has been extended to include effects of a coating layer with different thermal and optical properties than the substrate. The cases treated include one with an optically transparent coating and one with appreciable optical absorption.
Asymptotic solution for the reflectivity of a very rough surface
Authors: Tsang L. , Kong J. A.
Published: February 2003

Asymptotic solutions for the reflectivity of a very rough surface are obtained in closed form up to second order in variance of slope. The zeroth-order solution gives the reflectivity of a specular surface and the sum of the higher-order terms yields the net effect of the rough surface. Within the common regions of validity of small rms slope and incident angle not close to grazing, the result agrees very well with those obtained with numerical methods.
Oxidation of an aluminum magnetron sputtering target in Ar/O2 mixtures
Authors: Maniv S. , Westwood W. D.
Published: February 2003

The oxidation kinetics during sputtering of an Al target in a planar magnetron have been studied by accurate measurement of the total pressure produced by argon/oxygen mixtures. When a 5×8-in. target is rf sputtered at 500 W with a fixed argon flow, the pressure is constant at 4.6 mTorr until the oxygen flow rate is increased to 2.1 cm3/min. At this critical flow, the total pressure increases to 7.85 mTorr in 100 min and the time dependence is explained by a parabolic oxidation rate. The equilibrium oxide thickness is about 100 nm and has been measured by determining the time necessary to cause a sudden increase from 180 to 290 V in self-bias voltage. When the target was oxidized, Al2O3 films were deposited at 3 nm/min, whereas Al was deposited in an argon discharge at 70 nm/min. The ratio in sputtering rates of Al and Al2O is a factor of 2 greater than predicted from calculated yield values. Before target oxidation, oxygen added to the system is gettered by the film until, at values just below the critical value, Auger analysis shows the films have a composition AlOx where 1<x<1.5.
Low voltage ZnO varistor: Device process and defect model
Authors: Selim F. A. , Gupta T. K. , Hower P. L. , Carlson W. G.
Published: February 2003

A new process is described for achieving the current-voltage characteristics of a ZnO varistor with a breakdown voltage less than 20 V. The structure has been made by using Ag contacts containing oxides of Bi and Pb which serve both as a diffusion source for grain and/or grain boundary doping, and as metallic contacts on polycrystalline ZnO substrate. The structure was also made by sputtering a layer of various metal oxides such as Bi2O3, Sb2O3, Co3O4, etc. and then evaporating contact metals. The device shows a nonlinear current-voltage characteristic when annealed at 800–900 °C in air. Annealing in N2 ambient however, results in linear I-V characteristics. The presence of certain critical additives such as Bi2O3 was found essential for the development of nonlinearity. Based on these observations and the known defect structure of pure ZnO, a defect model which takes into account the role of oxygen in developing the nonlinear behavior of the proposed device is presented.
Monte Carlo calculations of structure-induced electromigration failure
Authors: Schoen J. M.
Published: February 2003

Monte Carlo calculations of structure-induced electromigration failure in Al and Al-alloy films have been performed using the model of Attardo. Conducting lines are broken into nonoverlapping segments and the grain structure is simulated from an assumed lognormal distribution. Vacancy flux in each segment is computed and the time to failure of the interface between two segments is assumed to be inversely proportional to the vacancy flux divergence. The time to failure of the line is the minimum interface failure time. The distribution of electromigration failure times computed in this fashion is found to follow logarithmic extreme value statistics; however, lognormal statistics are adequate when linewidth exceeds median grain size. Caution must be exercised in interpreting the results of the present work when grain size exceeds linewidth because surface electromigration may play a dominant role in determining the median time to failure. The variation of median time to failure and standard deviation derived here agrees well with experiment.
The effects of focusing in the three-frequency parametric upconverter
Authors: Guha Shekhar , Falk Joel
Published: February 2003

This paper extends the theory of parametric upconversion to describe the mixing of two focused optical beams with unequal confocal parameters. The results of this paper have greatest applicability when focusing of one input beam is limited by physical constraints, e.g., damage. The effects of phase matching, walk-off, and diffraction are treated herein. The analysis shows that if the beams have fixed confocal parameters b1 and b2, optimum mixing generally occurs with b2≠b1. If both confocal parameters can be arbitrarily chosen, maximum efficiency occurs with b1=b2= (crystal length)/2.84 in the absence of Poynting vector walk-off, and with b1≠b2 in the presence of walk-off. For weak focusing upconversion efficiency is written in a closed form which shows explicitly the effect of walk-off.