bluuebunny/crossref_metadata_2025 huggingface dataset:
Barkhausen noise controlled by electric current through core
Authors: Dalpadado R. N. G. , Shirae K.
Published: February 2003

Barkhausen noise, thought of as mainly due to sudden irreversible jumps in the moving domain wall, can be controlled significantly by passing suitable galvanic currents (Iz) through the magnetic core. For example, the maximum jump amplitude in the straight 2826 MB Fe40Ni38Mo4B18 amorphous ribbon in as-quenched state, excited by a 260 A/m, 0.001 Hz longitudinal field, and subject to an axial tensile stress of 1.6×106 N/m2, may be suppressed approximately 75 precent by a core-current of 3.4×106 A/m2 (2 A through 12mm×50μm section), the decrease in amplitude being roughly linear over the Iz range. Similar reductions in magnetic noise have been observed in other tape cores, especially amorphous. For higher excitation frequencies (45 Hz), the fluctuation noise superposed on the output voltage waveform may be eliminated by a lower curent Iz. The method of current-in-core is also applicable to samples subject to shear forces as twist. A simple model for the magnetization is presented as one to explain this process, based on the Néel spike domain model for Iz = 0. Also, the output voltage amplitude can remain nearly constant with the application of Iz while the fluctuation noise is suppressed, giving improved S/N ratio, under suitable conditions.
The uniaxial ferromagnet NiZrF6⋅6H2O in a transverse field
Authors: Lecomte G. V. , Karnezos M. , Friedberg S. A.
Published: February 2003

The magnetic susceptibility of trigonal crystals of the uniaxial ferromagnet NiZrF6⋅6H2O has been measured parallel to the easy (trigonal) axis between 0.08 and 5K in a 3He-4He dilution refrigerator by a mutual inductance method at 70 Hz. Data have been obtained with static fields, H⊥, up to ∼3000 Oe applied perpendicular to the easy axis. Keeping the amplitude of the oscillatory field below 1 Oe, χ∥ is found to exhibit a sharp peak at the Curie point Tc = 0.16K for H⊥ = 0. This peak remains sharp in the presence of large transverse fields indicating the persistence of the cooperative ferromagnetic ordering transition. The peak shifts to lower temperature with increasing H⊥ tracing out a boundary in the H⊥-T plane separating ferro- and paramagnetic regions. This phase diagram is in reasonable agreement with predictions for models of uniaxial ferromagnets.
High field NMR studies of static ordering and spin energy coupling in MnF2
Authors: Das S. , Patz S. , Heller P.
Published: February 2003

The antiferromagnetic to paramagnetic transition in MnF2 in a 75kG field applied along [001] has been studied using NMR. The time-average staggered and uniform magnetizations N and M were obtained respectively from the difference and sum of the NMR frequencies of the two 19F sites α and β, over the range .12 °K<Tc−T<6 °K. The critical behavior of the order parameter N was found to be very similar to that seen in low fields, as expected. Of particular interest were the NMR linewidth and shape behaviors in the ordered phase, as these bear on the coupling of N and M to the spin system thermal diffusion mode there. The data analysis employed least squares shape fitting. Excellent Lorentzian fits were obtained where expected. The fitted values of Γ = 1/T2 were combined to yield the site average Γ̄ = (Γα+Γβ)/2 and site difference ΔΓ = Γβ−Γα. Here Γ̄ was found to diverge critically, although not with power-law behavior, while ΔΓ was found to be slowly varying and ∼.25×106sec−1. These results are interpreted using the Kubo-Tomita-Moriya formalism, together with a rudimentary theory incorporating a wave-vector dependent extension of the Landau-Placzek ratio.
Dependence of anisotropy field on magnetization in iron
Authors: Hanham S. D. , Arrott A. S. , Heinrich B.
Published: February 2003

The temperature dependences of anisotropy and magnetization of iron are extracted from measurements of the field dependence of the ac susceptibility in [111] and [100] oriented iron whiskers. To do this the demagnetizing field is calculated taking into account the effects of anisotropy. The temperature range covered is from room temperature to within 0.5 deg of the Curie temperature.
Have solitons been observed in CsNiF3? (invited)
Authors: Reiter G.
Published: February 2003

The lowest order spin wave theory for CsNiF3 is presented and compared with neutron scattering experiments and the predictions based on the dilute soliton gas model. We conclude that further experiments and theoretical development are necessary to distinguish the soliton contribution to the central peak intensity from the scattering by pairs of spin waves.
Anisotropic quantum spin chains
Authors: Kurmann J. , Müller G. , Thomas H. , Puga M. W. , Beck H.
Published: February 2003

We have studied two models for anisotropic quantum spin chains. (i) XY-chain with a field in the plane: The magnetization of the ferromagnet behaves as h1/3 for small fields, in agreement with scaling laws. The antiferromagnet shows a critical field at which the ground state is a simple Néel state and which separates power law from exponential decay of spatial correlations. (ii) Anisotropic XY-chain: The dynamic z-component spin correlation function can be decomposed into a spin wave and a soliton contribution. The nature of quantum soliton excitations is studied and their form compared to soliton solutions of classical equations of motion.
Transverse spin dynamics in CsCoCl3
Authors: Nagler S. E. , Armstrong R. L. , Buyers W. J. L.
Published: February 2003

CsCoCl3 is believed to be an excellent example of a one dimensional s = 1/2 Ising-like antiferromagnet with a ratio of transverse to longitudinal exchange of ε∼0.1. High resolution inelastic neutron scattering measurements have yielded the result that the zone centre spin wave response is broad and strongly asymmetric, with a significant fraction of the spectral weight in a narrow peak at the low frequency end of the distribution. At the zone boundary a sharp resolution limited peak is observed. We report further high resolution measurements of the spin wave response in CsCoCl3. The calculations of Ishimura and Shiba based on first order perturbation theory as well as exact calculations on rings of 10 spins predict too little spectral weight in the low frequency sharp feature. In addition, the perturbation theory fails to describe the bandwidth and dispersion of the peaks with a single value of ε. It is unlikely that perturbation theory to order ε is adequate for CsCoCl3.
Quantum effects in spin dynamics of one dimensional systems (invited)
Authors: Beck H. , Puga M. W. , Müller G.
Published: February 2003

We present a review of recent results concerning dynamical spin correlation functions of quantum spin chains with nearest neighbor exchange interactions. Zero and finite temperature results, as well as the influence of a magnetic field are discussed for s = 1/2, with special emphasis on quantum effects which can be observed experimentally. We also investigate the dependence on spin quantum number between extreme quantum (s = 1/2) and classical (s = ∞) systems.
Ferromagnetism in one dimensional systems: synthesis and structural characterization (invited)
Authors: Willett Roger D. , Landee Chris P.
Published: February 2003

Synthetic strategies for designing new 1d magnetic systems are presented. A review is given of some of the structural characteristics which lead to ferromagnetic interactions between metal ions. Results of application of these concepts to the preparation of new quantum 1d systems with ferromagnetic coupling are presented. Special emphasis is given to recent discoveries of spin 1/2 copper (II) salts which have large intrachain coupling.
An infinity of commensurate phases in a simple Ising system: The ANNNI model (invited)
Authors: Fisher Michael E.
Published: February 2003

The ANNNI or axial next-nearest neighbor Ising model in d dimensions consists of (d−1)-dimensional layers of Ising spins, si = ±1, with nearest neighbor ferromagnetic couplings, J0≳0, within layers but competing ferromagnetic, J1, and antiferromagnetic, J2 = −κJ1<0, axial couplings between spins in first- and second-neighboring layers. It is the simplest model expected to display spatially modulated magnetically ordered states with wavevectors nontrivially related to the lattice spacing a, as observed in various real systems. The ground state is ferromagnetic for κ<1/2; of (2, 2), or 〈2〉, antiphase character (two layers ’’up’’, two ’’down’’, periodically) for κ≳1/2; but infinitely degenerate for κ = 1/2. Systematic low-temperature expansions may be generated about all possible ground states and carried to all orders where necessary. For d≳2 they show that (T,κ) = (0,1/2) is a multiphase point from which spring an infinite sequence of distinct, spatially modulated commensurate phases, 〈2j−13〉, with wavevectors q̄ = πj/(2j+1)a for j = 1,2, ⋅⋅⋅ . The free energy, phase boundaries, and corresponding domain wall energies can be given explicitly at low temperatures. On approaching the ’’melting’’ line, κ∞(T), of the 〈2〉 phase the wavevector varies quasicontinuously as 1/‖1n[κ∞(T)−κ]‖, displaying a ’’devil’s top step’’ just as the 〈2〉 phase locks in.
A theory of the magnetic anisotropy of rare earth-iron compounds
Authors: Cullen J. R.
Published: February 2003

An expression for the magnetic anisotropy energy of a model of the ternary compounds RxR′1−xFe2 is derived. The fourth and sixth-order crystal field energies are treated as a perturbation on the rare earth-iron exchange. Using this expression, it is shown that, for certain ranges of x, the colinear phases are unstable to the formation of spin-canted phases in which the net magnetization points along nonmajor symmetry directions. DyxTb1−xFe2 is discussed as an example.
Neutron diffraction and magnetic studies of ErFe3
Authors: Kebe B. , James W. J. , Deportes J. , Lemaire R. , Yelon W. , Day R. K.
Published: February 2003

Neutron diffraction experiments have been carried out on the intermetallic compound ErFe3 at 4.2, 77, and 300K. At 4.2K the magnetic structure is collinear and the moments are along c↘. Using the Rietveld profile method, both collinear and noncollinear models gave satisfactory agreement with the neutron data at 77 and 300K. Single crystal magnetization measurements allowed us to resolve this uncertainty in favor of a noncollinear structure at 77K and gave evidence for a basal plane structure at 300 K. At zero field a reorientation of the magnetic moments occurs around Tc?40K. Sharp field induced transitions are observed when the magnetic field is applied either parallel (T≳Tc) or perpendicular (T<Tc) to c↘. It is argued that the magnetic behavior of ErFe3 results from the variation of the anisotropy constants of ErI, ErII, and Fe atoms with the temperature. We have closely related the field induced transitions and the reorientation of the moments observed at zero field.
Magnetic anisotropy of single crystal HoFe3
Authors: Lee R. W.
Published: February 2003

The magnetization of single crystal HoFe3 has been measured as a function of applied field direction and temperature for H⩽100 kOe and 20K⩽T⩽300K. The compound exhibits essentially easy-basal plane anisotropy with anisotropy fields in excess of 150 kOe. The easy magnetization direction remains b-axis throughout the temperature range but a significant spontaneous magnetization persists along the hard c-axis. Two alternative models for the magnetic structure are proposed which fit the observed field direction dependence of the net moment. Both require the Ho moments to depart the basal plane for field directions other than b⃗.
Magnetic properties of some RAuGa intermetallic compounds
Authors: Sill L. R. , Hitzman C. J.
Published: February 2003

The magnetic moments of the series of intermetallic compounds RAuGa, where R is Sm or one of the heavy rare earth elements, has been measured at temperatures from 2.5 °K to 300 °K in applied fields up to 26kOe. These compounds form in an orthorhombic crystal structure and are isostructural with TiNiSi (a distorted AlB2-type structure). At high temperatures the reciprocal susceptibility of all the compounds except Sm follows a Curie-Weiss law; the effective paramagnetic moments are in good agreement with those calculated for free tripositive rare earth ions. The Curie paramagnetic temperatures of the heavy rare earth compounds do not vary linearly with the de Gennes function. At low temperatures only the Gd compound exhibits magnetic ordering. It orders antiferromagnetically with a Neel temperature of 6 °K. It also exhibits metamagnetic behavior. For the other compounds no magnetic ordering is observed although at the lowest temperatures the Tb and Dy compounds give an indication of being close to ordering.
NMR study of the exchange interactions and conduction band polarisation in ErFe2
Authors: Berthier Y. , Devine R.A.B.
Published: February 2003

The nuclear magnetic resonance of 167Er in ErFe2 and Er0.9 La0.1Fe2 has been studied at 1.2K using pulse spin-echo-techniques. We have observed ’’satellite’’ spectra in Er0.9La0.1Fe2. From the observed spectra in both compounds, the various contributions to the hyperfine field seen by the Er nucleus are deduced. Preliminary spin-lattice relaxation time measurements suggest the Weger mechanism (relaxation via magnon-conduction electron coupling) to be predominant.
Evidence of short range magnetic order at four times Tc in a metallic compound containing Fe: Susceptibility and paramagnetic scattering in CeFe2
Authors: Déportes J. , Givord D. , Ziebeck K.R.A.
Published: February 2003

Below 230 K CeFe2 orders with a saturation magnetic moment of 1.15 μB/Fe at 4.2 K. The paramagnetic effective moment deduced from the Curie-Weiss law is 3.7 μB. Reported here are the results of neutron paramagnetic scattering measurements obtained between 300 K and 870 K on CeFe2. The technique of polarization analysis has been used to obtain a unique measurement of the magnetic cross-section. The Fe moment determined in this way is about 1 μB, close to that observed in the ferromagnetic state. However, strong ferromagnetic correlations are found to persist up to the highest temperature used in this study, i.e., 870 K. The results are in complete agreement with recent theories which tend to reconcile 3d band magnetism with the persistence of a moment in the paramagnetic state. In conclusion, effective moments derived from susceptibility measurements do not allow an understanding of the 3d magnetism in the paramagnetic state.
A study of structure order of R(CoCu)5 compounds
Authors: Yang Ying-chang , Ho Wen-wang , Lin Chin , Yang Ji-lian , Jin Lan , Zhu Jia-xuan , Zeng Xiang-xin
Published: February 2003

We made use of neutron diffraction to study the crystal structure of R(Co1−xCux)5, in which x = 0.0, 0.2, 0.4, and 0.6, R = Y and Ce. From the analysis of neutron diffraction spectra, we found the Cu atoms prefer to occupy the 2c site. Meanwhile, we studied the thermal expansion behavior of CeCo5 and Ce(CoCu)5 compounds by high temperature x-ray. It showed an invar-type thermal expansion anomaly in the axis c below the Curie temperature. The anomalies are considerably reduced on the partial substitution of the Co atoms by the Cu atoms. All of these characteristics can be explained with the order of the substitution of Co atoms by Cu atoms.
Temperature dependence of magnetocrystalline anisotropy energy and saturation magnetization of GdNi single crystal
Authors: Sato Kiyoo , Koyachi Katsuichi , Mori Katsunori
Published: February 2003

The temperature dependence of the magnetocrystalline anisotropy energy and saturation magnetization was measured in single crystals of GdNi. Anisotropy constants K1 and K3 are estimated to be K1 = 4.0×106 erg/cm3 and K3 = −2.7×106 erg/cm3. It was found that the torque is proportional to the square of the magnetization for the GdNi compound. The microscopic origins of the anisotropy energy are discussed.
New properties associated with the occurrence of d-band magnetism in the Y-Ni compounds
Authors: Gignoux D. , Lemaire R. , Molho P. , Tasset F.
Published: February 2003

Among the Y-Ni compounds, four different behaviours, characteristic of the occurrence of d ferromagnetism in intermetallics have been observed : Exchange Enhanced Pauli Paramagnetism in YNi5 and YNi2, Very Weak Itinerant Ferromagnetism in YNi3, Collective Electron Metamagnetism in Y2Ni17 and Thermal Spontaneous Magnetization in Y2Ni7. The evolution of the magnetic properties as a function of the yttrium concentration is discussed in the light of the band structure of the different compounds.
Crystal field splitting of Gd3+ in the superconducting state of LaOs2
Authors: Luft H. , Baberschke K.
Published: February 2003

ESR measurements on Gd3+ in single crystals of LaOs2 in the superconducting state show a resolved cubic fine structure spectrum. The cubic crystal field parameter is determined as b4 = −18(2) Gauss. The temperature dependence of the resolved spectra below Tc is analysed in terms of the Barnes-Plefka theory, leading to an exponential temperature dependence of the impurity conduction electron relaxation rate δie in the superconducting state.
Fermi surface of paramagnetic and antiferromagnetic chromium
Authors: Fry J. L. , Brener N. E. , Laurent D. G. , Callaway J.
Published: February 2003

A linear-combination-of-Gaussian-orbitals band calculation is performed to determine the Fermi surface of paramagnetic chromium. This Fermi surface is compared with experimentally determined dimensions including those of antiferromagnetic chromium. By introducing a spin density wave it is possible to modify this band structure in a way which is consistent with both optical data and Fermi surface data from the low temperature antiferromagnetic structure of chromium.
Electrical resistivity of PrCu6 at the nuclear magnetic ordering transition
Authors: Kiely J. , Manley T. , Pontinen R. , Weyhmann W.
Published: February 2003

An experimental study of the ac impedance of PrCu6 near its nuclear magnetic ordering transition has been performed. At 40 Hz the data is consistent with a ferromagnetic resistive anomaly from a transition at 2.5–2.7 mK (Tc) and an antiferromagnetic or weak ferromagnetic resistive anomaly at 3.2–3.5 mK (TN). The two transitions were also observed in the magnetization and susceptibility data. The resistivity below Tc decreases as the square of the magnetization. The transition at TN is quenched by magnetic fields greater than 30 to 40 Oe.
Temperature variation of the magnetic inelastic neutron scattering from pure chromium
Authors: Booth J. G. , Ziebeck K. R. A.
Published: February 2003

The frequency and wavevector dependence of the magnetic INS response in pure chromium has been investigated over the temperature range 4 to 450 K (∼1.5 TN). At all temperatures the Q-dependence was centred on the (100) commensurate lattice position. The frequency dependence was found to differ in the ordered and paramagnetic phases. The transverse response in the AF1 phase at 295 K showed the following features: (i) for energy transfers <1 THz two peaks centred on (1±δ, 0, 0) were observed together with a small peak at (100), (ii) at higher energy transfer the response coalesced into a Gaussian shaped peak centred on (100) and (iii) for energy transfers ≳6.5 THz the response became strongly attenuated. This critical frequency is consistent with the expected energy gap, i.e., TN = 311K (6.5 THz). Moreover measurements in the paramagnetic range above TN did not reveal any attenuation for energy transfers up to 11 THz. In the AF2 phase region at 4.2 K energy scans parallel to the SDW vector showed a similar coalescence of the response on to (100) above 1 THz. The results are discussed in terms of excitations emanating from (100). In addition we put forward the idea of a non-linear dispersion owing to the small energy gap and discuss the implications.
T-S diagram for gadolinium near the Curie temperature
Authors: Benford S. M. , Brown G. V.
Published: February 2003

The magnetocaloric effect in polycrystalline Gd was measured at temperatures from 190 to 370 K in applied fields from 1 to 7 T. The magnetocaloric temperature changes were combined with existing zero-field specific heat data to construct a T-S diagram for Gd near the Curie point. Experimental values of ΔT were also compared with values calculated from a simple mean field theory, which predicts rather well both the general shape of the magnetocaloric curve and the relative magnitudes of the temperature changes in various measuring fields. The maximum ΔT with applied field was about 14 K at 7 tesla, and maxima in all applied fiels occurred near 292 K. The relatively large magnetocaloric effect in Gd near room temperature is attractive for potential magnetic refrigeration applications, and the experimental T-S diagram may now be used to refine estimates of the performance of Gd as a solid magnetic refrigerant.
Application of magnetization measurements in iron to high temperature thermometry
Authors: Arrott A. S. , Heinrich B.
Published: February 2003

It is proposed to use iron whiskers as elements for magnetic thermometers. The sharpness and reproducibility of the large second harmonic response that occurs just as the centre of the whisker saturates depends upon temperature through Ms(T). As a thermometer the whisker has a built-in fixed point which is reproducible to parts in 106. A one point calibration is needed to determined the demagnetizing factor. Suggestions are made for incorporating magnetic thermometers into thermocouples and resistance thermometers.
Effect of hydrostatic pressure on Curie temperature in amorphous (Fe1−xNix)90Zr10 alloys
Authors: Shirakawa K. , Kaneko T. , Nose M. , Ohnuma S. , Fujimori H. , Masumoto T.
Published: February 2003

A shift of the Curie temperature (ΔTc) taken place under the hydrostatic pressure (P) up to 12 kbar was measured for amorphous (Fe1−xNix)90-Zr10 alloys. The Curie temperature (Tc) was determined by the measurement of temperature dependence of initial permeability (μ). The Tc decreased linearly with P in the low pressure region for all of as-prepared specimens. The dTc/dP took the highest value of −3.8K/kbar for Fe90Zr10 and then rapidly decreased with Ni content, reaching about −0.1 K/kbar at x = 0.9. The curve of dTc/dP−1/Tc was linear for alloys with low Ni contents. This relation was consistent with the theoretical relation by Wohlfarth on the basis of weak itinerant ferromagnetism.
Numerical analysis of junction-depth effect in the grating-type Si solar cell
Authors: Hwang H. L. , Liu D. C. , Lin J. E. , Loferski J. J.
Published: February 2003

Numerical simulations are used to analyze the performance of Si grating cells. The alternating direction implicit method is used to solve the two-dimensional diffusion equations. For a fixed grating geometry, the optimum junction depth is determined. The performance of the deep-junction grating cells is contrasted with that of the more common shallow-junction cells. The results show that the performance of the cells is enhanced both by incorporating a back-surface field and minority-carrier mirrors into the grating structure. T;8184.60.Jt, 73.40.−c
Intrinsic noise characteristics of NbN SQUID’s
Authors: Cukauskas E. J. , Nisenoff M.
Published: February 2003

Thin-film NbN SQUID’s with granular weak links have been fabricated and their rf I-V characteristics measured at 23 MHz. Three different temperature variations of the critical currents were observed. A Josephson-like temperature dependence for those devices with strongly coupled grains and a bulk-mean-field-like dependence for those with the weakest coupled grains were found. An intermediate case where the critical current follows the bulk-mean-field theory at low critical currents and switches over to Josephson-like for larger currents was also observed. The noise properties of these devices were deduced from the measurement of the step rise parameter a. The data were in good agreement with the theory of Kurkijarvi over a wide range of temperature and critical currents for those devices with a bulk-mean-field-like critical current dependence and a low critical current density (∼104 A/cm2). Other devices were in agreement over a much smaller region of temperature and critical current. These devices are rugged, stable, and show very little change in their characteristics after extended storage at room temperature.
Pulsations in AlxGa1−xAs buried heterostructure lasers caused by the heating of defects
Authors: Henry C. H. , Logan R. A. , Merritt F. R.
Published: February 2003

The onset of pulsations in buried heterostructure lasers was investigated with a two-pulse method. First, an above threshold pulse was applied to reversibly convert the laser from a nonpulsating to a pulsating state. The pulsating state persists for several hundred nsec. A second pulse, applied 50 nsec or more after the first pulse, was then used to study the pulsations and other associated changes in the laser. In this way, a laser which initially does not even exhibit observable relaxation oscillations was changed into a laser which has sustained pulsations with a period of 1.8 nsec. These studies provide evidence that pulsations are caused by defects locally heated by absorbed laser light. Measurements of spontaneous emission intensity, laser threshold, and quantum efficiency showed that the loss in the laser cavity increased when the laser was converted into the pulsating state. The minimum loss increase observed to cause pulsations was about 13–19 cm−1. The characteristic time for the increase in loss to rise and fall was 100–200 nsec. These changes were nonexponential with both long- and short-lived components. Both the time scale and the nonexponential behavior are expected for the increased absorption loss associated with the heating of nonradiative defects. Calculations of defect heating predicted average temperature rises of 4–12 K, depending on defect size. It is estimated that a temperature rise of 7 K could halve the defect size necessary for pulsations. The increased loss correlated with the laser intensity during the first pulse, indicating that the heating is due primarily to the absorption of laser light, rather than to injected current. Local heating will promote pulsations by increasing the optical absorption and the change in gain with carrier density.
Temperature dependence of photoluminescence of n-InGaAsP
Authors: Temkin H. , Keramidas V. G. , Pollack M. A. , Wagner W. R.
Published: February 2003

The temperature dependence (from 6 to 300 K) of the near band gap photoluminescence (PL) of n-type InGaAsP is investigated. These layers, epitaxially grown on InP substrates, span the entire range of lattice matched compositions of the quaternary alloy. The spectral width of the PL emission and its temperature dependence are found not to vary with composition. However, compositional grading, especially evident at the center of the InGaAsP alloy range, often results in significant linewidth increase. These results are correlated with double crystal x-ray diffraction measurements. The experimental results are compared with predictions of van Roosbroeck–Shockley formalism.
Model for 1/f noise in metal-oxide-semiconductor transistors
Authors: Kleinpenning T. G. M. , Vandamme L. K. J.
Published: February 2003

At present there are two theories of 1/f noise in metal-oxide-semiconductor (MOS) transistors. One is based on the McWhorter model (number fluctuations), the other on the Hooge model (mobility fluctuations). In both theories the influence of high electric-field strengths on the mobility of carriers in the channel were left out of consideration. Here a new model of 1/f noise in MOS transistors is presented which is based on the Hooge model and takes into account the high electric-field strengths in the channnel. The theoretical results agree well with experimental results.
An evaluation of potentially low-cost silicon substrates for metal-insulator-semiconductor solar cells
Authors: Anderson W. A. , Rajeswaran G.
Published: February 2003

Cr metal-insulator-semiconductor solar cells were fabricated on special silicon substrates identified as 5-in.-diam Czochralski wafers, Wacker polycrystalline-Si, silicon on ceramic, and IBM ribbon. These cells produced open circuit voltages ranging from 0.58 to 0.48 V, short circuit current density from 32 to 18 mA/cm2, and efficiency from 11.5 to 5.1% depending on surface perfection and diffusion length. Spectral response data gave diffusion length values in a range from 150 to 39 mm. Calculations showed interface state density values ranging from 4.2×1012 to 1.2×1013/cm2 eV, which are quite high due to the surface nature of these substrates.
Characteristics of GaAs-anodic oxide metal-oxide-semiconductor solar cells
Authors: Das P. , Chakravarti S. N. , Bhat K. N.
Published: February 2003

Metal-oxide-semiconductor solar cells with reproducible photovoltaic characteristics have been fabricated on (n+) GaAs substrates employing an oxidation technique which combines an aqueous anodization method with a post-fabrication HC1 treatment. The cell typically displays an open-circuit voltage Voc of the order of 0.59 V and a short-circuit current density Jsc of 13.65 mA/cm2 under simulated AM1 illumination. An efficiency of 5.7 % has been achieved without antireflection coating.
Spin dependent attenuation lengths in ferromagnets
Authors: Rendell R. W. , Penn D. R.
Published: February 2003

Spin dependent attenuation lengths (AL) as a function of the hot electron energy are calculated for Fe, Co, and Ni. If λ↑(λ↓) is the AL of an electron with spin parallel (antiparallel) to the majority spin direction of the ferromagnet then the quantity A = (λ↓−λ↑)/(λ↓+λ↑) is found to change sign as a function of the electron energy.
A model for the structural and magnetic instabilities in the manganese perovskites
Authors: Jardin J-P. , Labbé J.
Published: February 2003

We propose a theoretical model for the band structure of metallic perovskites Mn3MN and we use it to calculate the electronic contribution to the Free energy variation associated with a lattice distortion and the occurrence of magnetism. We show that the position of the Fermi energy with respect to a sharp singularity in the electronic density of states in our model has a very large influence on the stability of the structural and magnetic phases, in agreement with experimental data.
Influence of pressure on de Haas-van Alphen frequencies in cobalt
Authors: Anderson J. R. , Schirber J. E.
Published: February 2003

The solid-helium phase shift technique has been applied for measurement of pressure derivatives of de Haas-van Alphen frequencies in ferromagnetic hcp cobalt. Our values for the β oscillations for the magnetic field H ∥ [0001] and the ε oscillations for H ∥ [101̄0] are (−1.9±0.2)×10−3 kbar−1 and (0.4±0.2)×10−3 kbar−1, respectively. These results, combined with the value for the α oscillations (H ∥ [0001]), (−1.4±0.3)×10−3 kbar−1, have been used to examine models of the band structure of cobalt. An important contribution to these shifts with pressure is the transfer of electrons from majority-spin to minority-spin bands corresponding to the decrease in magnetic moment per atom of cobalt with pressure.
Charge and spin distributions in transition metal porphines and phthalocyanines
Authors: Ellis D. E. , Berkovitch-Yellin Ziva
Published: February 2003

Electronic energy levels and charge and spin distributions for iron, copper and silver porphine have been calculated, using the one-electron Hatree-Fock-Slater theory. Calculated spectroscopic properties are compared with the available optical, photoelectron, and hyperfine data, and with previous theoretical efforts. Using density difference contour maps and a Mulliken population analysis based upon the LCAO variational expansion of the eigenfunctions, we make quantitative verification of traditional ideas about bonding and charge transfer in these systems. Contact hyperfine fields and effective <r−3≳ matrix elements are obtained for various nuclear sites. Effects of substitution on the porphine carbon skeleton are studied in analogous calculations on the metal phthalocyanines. Subtle differences in metal-ligand bonding between porphines and phthalocyanines are revealed in the difference densities.
Electronic structure and itinerant magnetism in ZrZn2 and TiBe2
Authors: Freeman A. J. , Jarlborg T. , Koelling D. D.
Published: February 2003

The electronic and magnetic structure of the Cl5 compounds ZrZn2 and TiBe2 has been determined by means of self-consistent spin-polarized LMTO band calculations. The spin-densities and neutron magnetic form factors are compared with neutron scattering data for ZrZn1.9 and TiBe1.8Cu0.2. The moments are found to reside almost entirely on the Zr/Ti atoms, and are found to be 0.14 and 0.21 μB per formula unit respectively.
Temperature dependent dynamic susceptibility calculations for itinerant ferromagnets
Authors: Cooke J. F.
Published: February 2003

Inelastic neutron scattering experiments have revealed a variety of interesting and unusual phenomena associated with the spin dynamics of the 3-d transition metal ferromagnets nickel and iron. An extensive series of calculations based on the itinerant electron formalism has demonstrated that the itinerant model does provide an excellent quantitative as well as qualitative description of the measured spin dynamics of both nickel and iron at low temperatures. Recent angular resolved photoemission experiments have indicated that there is a rather strong temperature dependence of the electronic spin-splitting which, from relatively crude arguments, appears to be inconsistent with neutron scattering results. In order to investigate this point and also the origin of spin-wave renormalization, a series of calculations of the dynamic susceptibility of nickel and iron has been undertaken. The results of these calculations indicate that a discrepancy exists between the interpretations of neutron and photoemission experimental results regarding the temperature dependence of the spin-splitting of the electronic energy bands.
Resonant satellites in photoemission and Auger spectra of d-band metals (invited)
Authors: Girvin S. M. , Penn D. R.
Published: February 2003

Photoemission and Auger electron spectroscopy are powerful tools in the study of the electronic and magnetic properties of d band metals. In certain instances experimental spectra can be directly interpreted as a measure of some one body density of states. In other cases one must consider the many body dynamics of the measurement process in detail. Striking examples of the latter are the resonant satellites in several filled d band materials which have been observed in photoemission near the photon energy threshold for core hole production. An elementary introduction to the physics of this satellite phenomenon will be presented. A model recently introduced by Davis and Feldkamp to explain resonant satellites in filled d band materials will be discussed in some detail and the predictions of this model will be used to illustrate some general properties of resonant photoemission satellites.
The magnetism of iron and nickel (invited)
Authors: Hubbard J.
Published: February 2003

A type of theory which unifies the itinerant and localized models for metallic ferromagnets is discussed. The results of some calculations for iron and nickel are described. In particular it is found that this model can give both the correct ground state moment and Curie temperatures of the right order of magnitude (Tc = 1840 °K for iron and 1200 °K for nickel).
Transition metal impurities in CoGa
Authors: Benesh G. A. , Ellis D. E.
Published: February 2003

Isolated transition metal impurities on Ga sites in β-phase CoGa have been studied by treating 9, 15, and 27-atom clusters representative of the compounds Co2Ga2−xMx(M = Ti, V, Cr, Co), for small values of x. Self-consistent calculations performed on MCo8 and MCo8Ga6 clusters give an incomplete description of the local magnetic environment of off-center Co atoms. The addition of a new shell of atoms, so that 7 of the 8 nearest neighbors of these Co atoms were explicitly included in the cluster, led to marked reduction of spurious peripheral atom magnetization. Results for the MCo8Ga6Ga12 clusters, indicate that isolated impurity atoms on Ga sites are non-magnetic, in agreement with experimental interpretations.
Diffuse magnetic elastic scattering of neutrons from Cr-Fe and Cr-Co alloys
Authors: Costa M. M. R. , Booth J. G. , Ziebeck K. R. A. , Brown P. J.
Published: February 2003

The diffuse magnetic elastic scattering from powder samples of Cr-12 at % Fe and Cr-10 at % Co has been obtained at temperatures above and below TN. Polarized neutrons and polarization analysis were used on the D5 instrument at I. L. L. Grenoble to obtain a unique determination of the magnetic scattering. For the Cr-Fe alloy forward scattering was observed both above and below TN without significant change in magnitude or Q-dependence. The magnitude was consistent with that expected from susceptibility measurements. The fall-off with increasing Q was more rapid than that anticipated for a typical 3d form factor tending towards zero at (sinϑ)/λ∼0.15 Å−1. In contrast, the response of the cobalt-containing alloy was suppressed below TN although of a similar form to the Fe alloy above TN. This suppression could be associated with a locking of the Co moments to the SDW. The incoming neutrons (λ = 0.84 Å) have energy ∼115 meV and with an analyser-detector window of 20 meV any locking of the Fe moments (with coupling constants of ≲4 meV) would not be detected.
Ferromagnetism in the RhGd and PtGd systems
Authors: Smith J. L. , Fisk Z. , Roof R. B.
Published: February 2003

Rhodium and platinum have been studied with up to 33% additions of gadolinium. The magnetic properties of the constituents in the layers of a eutectic structure are different from the bulk properties of the constituents. The compound GdPt5 orders ferromagnetically at 13.9 K.
Ordering in the infinite-ranged Ising spin glass—Exact solutions for small samples
Authors: Kirkpatrick Scott , Young A. Peter
Published: February 2003

A new order parameter q(2) for the infinite-ranged Ising spin glass model is introduced. q(2) can be defined without specifying any symmetry breaking field, and is a direct measure of the effect of frustration on the internal energy below the spin glass transition temperature, Tsg. An exact evaluation of q(2)(T) for small systems (with up to 20 spins) establishes the existence of Edwards-Anderson ordering, and sheds light on several of the controversies which surround this model.
Ground state properties of dilute classical fcc Heisenberg antiferromagnets with nearest-neighbor interactions
Authors: Ching W. Y. , Huber D. L.
Published: February 2003

We investigate the ground state properties of a classical fcc Heisenberg antiferromagnet with nearest-neighbor interactions. It is assumed that a fraction x of the sites are occupied at random. The ground state energy and rms magnetization are obtained as a function of x for 0.1⩽x⩽1. Numerical calculations are carried out on finite arrays of 102−103 spins. Equilibrium configurations are obtained by successively rotating each spin into the direction of its local field. Unusual features of the ground states of the fully occupied lattice (x = 1) are pointed out and a comparison is made with comparable results for the analogous fcc Ising antiferromagnet.
The effect of RKKY interactions on the magnetization of dilute magnetic alloys with hcp hosts
Authors: Gash P. , Roshko R. , Symko O. G.
Published: February 2003

The magnetization due to the presence of magnetic impurities dissolved dilutely in nonmagnetic H.C.P. host metals has been calculated assuming a fine structure splitting by an axially symmetric crystal field and an RKKY interaction between the impurities. To compute the RKKY contribution, the interaction between the impurities is described by a randomly oriented effective internal exchange field H with a probability distribution P(H↘) = Δ/π2(Δ2+H2)2. Comparison of the calculated magnetization with the measured magnetization of a 5 ppm single crystal of MgMn and several polycrystalline ZnMn samples of varying concentration, over the temperature range 2K to 10mK, yields estimates for Δ, the most probable value of the magnitude of the effective exchange field, as well as the dependence of Δ on impurity concentration.
Two magnon response functions in random magnets
Authors: Thorpe M. F. , Miyazima S.
Published: February 2003

We extend the equation of motion method1 that was developed to compute one magnon response functions in random magnets, so that we can now compute two magnon response functions. It is shown that if the interactions between the magnons are neglected, the two magnon response can be written as a convolution of one magnon responses and obtained by a trivial extension of previous work for square nets of size up to 100×100. Including interactions complicates the situation considerably. We write equations of motions for two spin operators and apply the equation of motion technique to these equations. It has been possible to get results for square nets up to 13×11 in size. We present results for the dilute Heisenberg ferromagnet on a square net.
Magnetic properties of amorphous (Co1−xNix)75P16B6Al3
Authors: Yeshurun Y. , Rao K. V. , Salamon M. B. , Chen H. S.
Published: February 2003

The temperature and field dependence of the magnetization in a series of amorphous Co-Ni alloys is reported. We discuss the critical behaviour and introduce a phase diagram which includes paramagnetic, ferromagnetic (FM) and spin glass (SG) phases. A T3/2 dependence for the magnetization is established in the FM phase. Deviations from spin wave theory which are observed in alloys with a FM-SG transition are discussed in terms of single spin excitations.
Mössbauer studies of magnetic ordering in amorphous (FexMn1−x)75P16B6Al3 under external magnetic fields
Authors: Chien C. L. , Hsu J. H. , Viccaro P. J. , Dunlap B. D. , Shenoy G. K. , Chen H. S.
Published: February 2003

57Fe Mössbauer spectroscopy under external magnetic fields of up to 72 kOe has been used to study the magnetic ordering in amorphous (FexMn1−x)75P16B6Al3 (0.25⩽x⩽1) at 4.2 K. From the behavior of the magnetic hyperfine fields one concludes that the Fe-rich samples are soft ferromagnets and the Mn-rich samples exhibit spin glass-like properties. In the samples with intermediate Fe concentrations, a magnetic ordering where both ferromagnetic and spin glass-like orderings coexist occurs.
Reversibility and time dependence of the magnetization in Ag:Mn and Cu:Mn spin glasses
Authors: Chamberlin R. V. , Hardiman M. , Orbach R.
Published: February 2003

We report dc-magnetization measurements on Ag:Mn and Cu:Mn spin glass samples (1–8% Mn concentrations), at temperatures of 4–30 K, and in fields of 4–400 Oe. The temperature at which the magnetization of a particular sample becomes reversible (TR) is found to depend on the homogeneity of the sample, and on the magnitude of the measurement field. Inhomogeneous samples showed irreversible behavior far above the glass temperature (TR≃1.5 TG). After annealing, these samples showed a sharper peak in the magnetization at TG∼TR. We feel this is strong evidence toward a unique glass temperature for homogeneous samples in low fields. In higher fields (400 Oe) we found reversibility to begin at a temperature less than the magnetization peak (TR≃0.9 TG for 4% Ag:Mn).
Simultaneous ESR and magnetization measurements characterizing the spin glass state
Authors: Schultz S. , Gullikson E. M. , Fredkin D. R. , Tovar M.
Published: February 2003

We have observed two ESR modes in a CuMnNi spin glass alloy. Both modes are interpreted with a phenomenlogical theory incorporating an order parameter, remanent magnetization, and anisotropy energy. From simultaneous magnetization and ESR measurements we are able to deduce the temperature and concentration dependence of the anisotropy constant, which has interesting scaling properties. The angular dependence of the field cooled ESR and magnetization data suggest the need for another order parameter which vanishes at Tg.
Spin glass properties of (Ti1−xVx)2O3
Authors: Miyako Y. , Chikazawa S. , Saito T. , Yuochunas Y. G.
Published: February 2003

The magnetic behavior of (Ti1−xVx)2O3 was studied in detail around the spin freezing temperature Tg. The magnetization m of spin glass is expanded around Tg as a function of the magnetic field, h = hocos ωt, as m = χoh+χ2h3+χ4h5+⋅⋅⋅ . First, ω and ho dependences of ‖χ2‖ are studied as well as χo. ‖χ2‖ seems to become singular at Tg as ω and ho are decreased. Second, the imaginary part of χo (Imχo) increases very steeply from above about 10% of Tg and Tg is the inflection point of Imχo. d(Imχo)/dT behaves like a divergence as T approaches to Tg. This behavior shows the slowing down phenomenon of the (longitudinal) relaxation time.
Low temperature magnetization of dilute PdMn spin glasses: Evidence for a T3/2 behavior and absence of RKKY scaling
Authors: Thompson J. R. , Thomson J. O.
Published: February 2003

We have made magnetization measurements with a SQUID magnetometer on four Pd1−xMnx alloys with x ranging from 27 to 575 ppm, at temperatures from 0.01 to 1 K and fields up to 250 Oe. Above 0.1 K the low field magnetization for all alloys is described by a Curie–Weiss law with a giant moment (g = 3.7 for S = 5/2) per Mn atom and with a ferromagnetic Weiss constant proportional to Mn concentration, ϑ = (130x) K. Below 0.1 K deviations from Curie–Weiss behavior are apparent. At the lowest temperatures the magnetization for the three lower concentration alloys follows the law M(H,T,x) = M(H,O,x)(1−α(H,x)T3/2). For the noble metal spin glasses we have shown previously that α(H,x) and M(H,O,x) follow scaling laws based on the r−3 oscillatory RKKY interaction. For these dilute PdMn alloys these scaling laws are not obeyed. This is further evidence at lower concentration that inter-impurity interactions in PdMn are not governed by the conventional RKKY indirect exchange.
Effect of magnetic dilution on χ⊥ in the random antiferromagnets MnxZn1−xF2 and FexZn1−xF2
Authors: King A. R. , Jaccarino V.
Published: February 2003

We have studied the effect of magnetic dilution on the low-temperature perpendicular susceptibility χ⊥ in two random antiferromagnets. Measurements as T = 4.2 K in MnxZn1−xF2 show a dramatic increase in χ⊥ with dilution, while in FexZn1−xF2, a small decrease is seen. This contrast can only be due to the difference between the small dipolar anisotropy in MnxZn1−xF2 and the large single-ion anisotropy in FexZn1−xF2. since the materials are otherwise very similar. We have explored several models in order to understand these effects. The initial slope χ′ of χ⊥ vs. x has been studied both with computer simulation and with a continuum model, in good agreement in both cases. The full dilution problem has been studied by computer simulation, which agrees very well with the data in both materials studied, and the initial slope χ′.
Computer modelling of spin distributions in amorphous RE-TM alloys
Authors: Sharma Y. P. , Pickart S. J. , Saw C. K.
Published: February 2003

Using the spatial coordinates from a previously described dense random packed model of a binary alloy, we have calculated the magnetic interference functions for two possible spin arrangements of amorphous TbFe2 for comparison with magnetic scattering data. The models investigated were ferromagnetic (all spins parallel) and ferrimagnetic (Tb and Fe spins antiparallel). Sensitivity of the interference function to changes in spin magnitudes and model size was also investigated. Although there are some differences between the calculated intensities from the two models, neither of them is in sufficiently good agreement with the data to be selected as definitive.