bluuebunny/crossref_metadata_2025 huggingface dataset:
19F spin-lattice relaxation in antiferromagnets with the perovskite structure
Authors: Engelsberg M. , Rezende S. M. , Soares E. A.
Published: February 2003

The results of the 19F spin-lattice relaxation rate measurements in single crystal KNiF3 as a function of temperature are reported. In the temperature range TN≳T≳0.05 TN (TN=246 K) two clearly different relaxation mechanisms are effective. At low temperatures (T<26 K) the relaxation rate 1/T1 increases slowly with temperature. At higher temperatures the variation with temperature is much faster. The data as a function of a reduced temperature show a striking similarity with previous results for another simple perovskite antiferromagnet, RbMnF3, suggesting that in both temperature ranges the relaxation is due to intrinsic processes. Various possible relaxation mechanisms are discussed.
Fluctuations near the percolation threshold in two and three dimensions
Authors: Birgeneau R. J. , Cowley R. A. , Shirane G.
Published: February 2003

A series of quasielastic and inelastic neutron scattering experiments have been performed in the diluted insulating antiferromagnets, Rb2MncMg1−cF4, Rb2CocMg1−cF4, MncZn1−cF2 and KMncZn1−cF4. The concentrations c were chosen so as to span the percolation threshold value c=cp; for c<cp no long range order is observed. We describe briefly the results of these experiments with special emphasis on the development of the magnetic correlations at low temperatures for samples with c?cp.
Crossover relationship between the magnetic susceptibility and the correlation length
Authors: Nicoll J. F. , Chang T. S.
Published: February 2003

In the asymptotic critical region of a ferromagnetic spin system, the magnetic susceptibility χ and the correlation length ξ are related by the power law: χ∼ξ2−η, where η is the correlation function exponent. Somewhat farther from the critical point, but still within the critical region, we expect the behavior to be mean-field in character: χ∼ξ2. We give an exact relationship between χ and ξ in terms of a differential renormalization group approach. The leading behavior in the disordered phase is explicitly calculated for the n-component Wilson-Fisher model to O(ε2), ε≡4−d. The result includes both limiting power laws in a smooth crossover function. For the Ising case, n=1, the relationship is extended to the entire critical region, including the ordered phase. In this case, even in the asymptotic limit, the susceptibility differs from ξ2−η by a factor which depends on the magnetization M. This function is calculated to leading order and correctly gives the associated amplitude ratios to O(ε). Applications to the general p-point vertex function are discussed.
Magnetically linear and quadratic hexanitrocuprates
Authors: Blöte H. W. J.
Published: February 2003

Magnetic and caloric measurements on potassium lead hexanitrocuprate, K2PbCu(NO2)6, agree well with the theory for an antiferromagnetic Heisenberg linear S=1/2 chain. Results for a related compound, in which lead is replaced by barium, can be analyzed in terms of an antiferromagnetic Heisenberg S=1/2 simple quadratic lattice. These classifications are supported by existing data on the crystal structures of these compounds at low temperatures.
Anomalous critical behaviour of the electrical resistivity of iron-platinum invar alloys
Authors: Viard M. , Gavoille G.
Published: February 2003

Resistivity measurements carried out on Fe3Pt invar alloys do not reveal a λ type anomaly near the Curie temperature Tc as usually observed on ferromagnetic materials. The Fe3Pt ordered alloy shows two very narrow peaks near Tc and a partially ordered alloy does not show any anomaly. As the Fe3Pt alloys are well known for their strong invar effect, we believe that such a behaviour results from critical electron-phonon scattering arising from the strong lattice softening near Tc. Attempted explanation is given based on bulk modulus data.
Ultrasonic attenuation in a cooperative Jahn-Teller system: TmZn
Authors: Leung K. M. , Huber D. L. , Lüthi B.
Published: February 2003

A general expression for the ultrasonic attenuation coefficient α (T) in systems undergoing strain-induced cooperative Jahn-Teller transitions has been derived. The theory makes use of the temperature dependent line widths of the crystal field manifolds. These have been calculated assuming the damping comes from aspherical coulomb scattering involving the rare-earth (RE) ion and the conduction electrons. With the theoretical expression for α (T) and the widths we make a comparison with experimental results for the RE intermetallic compound TmZn.
Elastic constants of single crystal uranium monosulphide
Authors: du Plessis P. de V. , Tillwick D. L.
Published: February 2003

Measurements are reported for the temperature dependence of the single crystal elastic constants C11 and C44 of US in its para- and ferromagnetic regions. A softening of C11 sets in from approximately 20 K above Tc to exhibit a minimum at Tc. The shear constant C44 undergoes a softening over the entire paramagnetic region to reach a maximum change of 15% at Tc. This latter behavior is reminiscent of the paramagnetic temperature dependence of C44 in UO2.
Abstract: Novel multicritical points of ’’weak metamagnets’’
Authors: Kerszberg M. , Mukamel D. , Rohrer H. , Thomas H.
Published: February 2003

Results of molecular-field calculations of phase diagrams, of uniaxial, and biaxial antiferromagnets with intermediate anisotropy are reported which exhibit novel multicritical points combining features of both bi- and tri-critical points. The limiting strength of anisotropy for having bi- or tri-critical behavior is found to depend strongly on the direction of applied field. (AIP)
Abstract: Spin dynamics in the linear antiferromagnet TMMC: Effect of a magnetic field at low temperature
Authors: Boucher J. P. , Jug G. , Borsa F.
Published: February 2003

We present an investigation of the effect of an applied external magnetic field on the low temperature spin dynamics of the linear antiferromagnet (CH3)4NMnC13 (TMMC). The theoretical results without adjustable parameters are compared with experimental values obtained for H, D, and 14N in the field range 1–77kOe and in the temperature interval 1.5–4K.; in high fields the comparison is satisfactory while at low fields there appears to be an extra contribution to the spin-lattice relaxation not included in the theory. (AIP)
Abstract: Observation of the spin-flop transition of MnF2 by neutron diffraction
Authors: Felcher G. P. , Kleb R. , Jaccarino Vincent
Published: February 2003

In a polarized neutron experiment, the diffraction lines of the basal plane of a single crystal of MnF2 were studied as a function of an external field rather well aligned (0.2°) with the c-axis of the crystal; above 92.7 Koe (at 4.2K) the magnetic response of the normal lattice lines increases suddenly as for an induced magnetization of ∼0.4 μB/Mn. In the spin flop state the polarization dependence of the intensities of the superlattice lines indicates that the magnetic moments lie largely in the basal plane. (AIP)
Zero wave vector kinetic coefficient in the isotropic ferromagnet EuO near Tc
Authors: Gottlieb Albert M. , Dunlap Richard
Published: February 2003

We have measured the zero wave vector kinetic coefficient and relaxation time for the isotropic Heisenberg ferromagnet EuO using zero-field electron spin reasonance. Measurements were made by monitoring the absorptive part of the uniform susceptibility χ (q=0,ω;T) at fixed frequency, ω/2π?20MHz, as a function of applied field. The zero wave vector kinetic coefficient asymtotically approached a constant value, conventional behavior, as the critical temperature was neared from above. Our measurements are consistant with a crossover of the dynamical critical exponent z from 5/2 to ?2 in the region 4πχ≳1, where the dipole interaction dominates.
Crossover from divergent to non-divergent nature of the ordered to paramagnetic transitions of α-MnCl2⋅4H2O as a function of applied field
Authors: Butera R. A. , Moskaitis R. J. , Rutter D. R. , Obermyer R. T.
Published: February 2003

The thermodynamic functions CH, (∂M/∂T)H and [(∂M/∂H)T– (∂M/∂H)S] have been determined as a function of temperature over the range 0.5 to 2.0 K for a spherical single crystal of α–MnCl2⋅4H2O with magnetic fields up to 20 kG applied parallel to the c-crystallographic axis. The data clearly show that the lamba anomaly in [(∂M/∂H)T−(∂M/∂H)S] associated with the transition from the ordered to paramagnetic state changes character at the bicritical point and completely disappears for fields greater than 8.4 kG. The region for fileds greater than 8.4 kG also corresponds to apparent non-power law behavior of the heat capacity and (∂M/∂T)H. The bicritical behavior is shown to be consistant with that of a antiferromagnet with orthorhombic anisotropy.
Coherent potential approximation for randomly diluted uniaxial antiferromagnets : Application to Mn1−xZnxF2
Authors: Moreira F. G. Brady , Fittipaldi I. P.
Published: February 2003

A recently proposed CPA theory (Tahir-Kheli et al), for treating randomly diluted antiferromagnets with uniaxial anisotropy is revised. It is shown that such a procedure, which ignores dynamical effects occasioned by fluctuations in the local anisotropy field, leads to unphysical results beyond certain critical concentrations at which the theory breaks down. A study of the weakness, the relevance and validity of this theory is presented. The theory is expected to be relevant only when applied to systems with relatively small anisotropy. In fact, owing to its simplicity, within its range of validity, we apply a such CPA to analyse the behaviour of the zero-field antiferromagnetic resonance in the mixed system of manganese and zinc fluorides as function of zinc concentration. Our results are compared with those from several recent experiments and a very good agreement is found. Moreover, the general features and complexity of an alternative CPA formalism which takes into account dynamical effects of fluctuations in both exchange and anisotropy fields, are also briefly discussed.
Magnetic studies on the dilute paired antiferromagnet RbMn1−xMgxCl3
Authors: Prater J. T. , Egami T.
Published: February 2003

Magnetic susceptibility and electron paramagnetic resonance experiments have been conducted on the RbMn1−xMgxCl3 system at temperatures ranging from 4.2 to 300 K and in magnetic fields up to 100 kOe. In the pure manganese compound the neighboring magnetic ions are alternately coupled by strong and weak exchange interactions, leading to a paired antiferromagnetic structure. The effect of diluting the manganese with up to 50% magnesium, a nonmagnetic species, has been examined. It is found that most of the results are consistent with what one finds in an ordinary diluted antiferromagnet. The notable exception exists in the concentration dependence of the ordering temperature. In the low dilution regime (x<.15) a nonlinear concentration dependence on the Neel temperature is found. This is attributed to the formation of chains of weakly interacting spins. These act to circumvent the magnetically stiff pairs produced at each of the strong exchange interactions, and thereby partially offset the effect of the broken magnetic bonds produced during the dilution process.
Fair effects in a bond model of a disordered Heisenberg ferromagnet
Authors: Kambe K.
Published: February 2003

We consider a bond model of a disordered Heisenberg ferromagnet in which spin values are equal to 1/2 but two distinct exchange integrals are distributed randomly among bonds. The coherent potential approximation in the form of Oguchi, Ono and Ishikawa is extended so as to include the pair effects of the bond clustering by adapting the treatment of the alloy problem by Schwartz and Ehrenreich. The self-consistency condition which determines the coherent exchange integral is derived. The density of states of magnons is calculated from the configurationally averaged Green function. The applications for the one-dimensional case and the two-dimensional case are discussed.
Abstract: Ferromagnetic and spin glass transition in Ni-Cu
Authors: Carnegie D. W. , Claus H.
Published: February 2003

Low field d.c. magnetization measurements on weakly ferromagnetic and spin glass-like Ni-Cu alloys are reported. (AIP)
NMR of Cu satellites in the Kondo alloy CuCr
Authors: Azevedo L. J. , Follstaedt D. , Narath A.
Published: February 2003

Using pulsed NMR techniques, resonances of Cu nuclei which are near neighbors to Cr impurities (c=100 and 200 ppm) in CuCr (ϑk∼3 K) have been studied in the temperature range 1–4 K and applied fields Ho=20–125 kOe. At the highest fields and lowest temperatures the satellite shifts approach saturation. Above ∼40 kOe the spin-lattice relaxation rate T1−1 is proportional to T/Ho2, indicating that the dominant relaxation mechanism arises from transverse fluctuations of a polarized local moment. The measured rates yield a local-moment/conduction-electron exhange interaction ‖𝒥ρ‖/g=0.30, where g is the Cr g-value. Below ∼40 kOe T1−1 appears to be slightly enhanced in comparison with the high-field behavior, but becomes field independent below ∼30 kOe. Both effects are attributed to Kondo anomalies.
Magnetic properties of crystalline Mg:Mn
Authors: Garvin R. W. , Wigen P. E.
Published: February 2003

A single crystal of Mg (hcp structure) with 0.35 atomic percent of the paramagnetic impurity of Mn was grown using the Bridgeman technique. From static susceptibility measurements an effective moment per Mn2+ ion of 5.6 Bohr magnetons, and a Weiss temperature of 3.4 K were determined. No evidence of a spin glass transition was found in the temperature range 2 K to 300 K. An axial crystal field parameter of D=126±7 Gauss was determined from the anisotropy in the ESR resonance field. Below 5 K a rapid downfield shift of the resonance field was observed. Anisotropy in the ESR linewidth at low temperature suggests the possibility of anisotropy in J, the exchange parameter between the local Mn2+ d electrons and the conduction electrons.
Thermomagnetic behavior of a duplex ferromagnetic alloy, Fe75Si15B10
Authors: Berkowitz A. E. , Livingston J. D. , Nathan B. D. , Walter J. L.
Published: February 2003

The chill-cast alloy Fe75Si15B10 consists of submicron Fe2B rods in a Fe3Si matrix. The magnetically ’’hard’’ Fe2B has a higher Curie temperature than the magnetically ’’soft’’ Fe3Si, which leads to unusual thermomagnetic behavior during cooling in low fields. When the thermoremanent magnetization (TRM) of the Fe2B produces a demagnetizing field greater than the applied field, the Fe3Si magnetizes opposite to the applied field, thereby reducing the net internal field. However, the magnetic heterogeneity of the sample prevents the net internal field from reaching zero. Significant magnetization changes are also noted in the temperature range where the magnetic anisotropy of Fe2B changes from easy-axis to easy-plane.
Theory of electronic structure of rare earth and actinide metals using Hubbard’s alloy approximation
Authors: Robinson John M.
Published: February 2003

We present a very general method for calculating the electronic excitation spectra and thermodynamic properties of solids with narrow hybridized f-bands. The theory is developed from the localized, atomic limit using the standard-basis operator (SBO) Green’s function formalism and greatly improves previous SBO treatments by going beyond the random-phase approximation (RPA). The present theory includes the scattering and resonance-broadening corrections and thus generalizes Hubbard’s s-band alloy approximation by incorporating an arbitrary set of atomic configurations.
Field and temperature dependence of thermodynamic and correlation functions of Hubbard model
Authors: Chen Charles C. , Huang Ming-Hui
Published: February 2003

The thermodynamic and correlation functions for one- and three- dimensional systems described by the half-filled band Hubbard Hamiltonians are evaluated in the pair-approximation of cluster variation method. The energy, specific heat, magnetization, susceptibility and various equilibrium correlation functions are computed as functions of temperature as well as the external magnetic field for different values of coulomb energies. Our solutions correspond to Bethe approximation in which the relevant pair-correlation functions are included in our formulation. It is observed that the chemical potential for the half-filled band is exactly half of the coulomb energy at all temperatures, irrespective of the value of the applied magnetic field.
Observation of solitons as a gas of quasiparticles in CsNiF3
Authors: Steiner M. , Kjems J. K.
Published: February 2003

An inelastic neutron scattering study of CsNiF3 in an external magnetic field at q6=0.1 r.1.u. revealed a central component in the energy spectrum besides the spinwave resonances. The temperature and field dependency of the intensity and the width of the central component could be well explained by the following picture: A 1-dimensional ferromagnet with planar anisotropy like CsNiF3 can be described by a sine-Gordon-Hamiltonian if a field is applied in the easy plane. The nonlinear excitations of this Hamiltonian appear in the neutron scattering experiment as a gas of thermally excited quasiparticles. The agreement between theory and experiment leads to the conclusion that the central component is due to scattering from thermally activated solitons.
Time-dependent correlation functions in the high-temperature limit for the XY-chain and the Ising-chain in a transverse magnetic field
Authors: Perk J. H. H. , Capel H. W.
Published: February 2003

Some exact results are presented for the time correlations between x- and y- components of spins (S=1/2) and their frequency-Fourier transforms in the one-dimensional XY-model in the high-temperature limit (β=0). The results show a predominantly Gaussian decay.
Spin waves in a Heisenberg antiferromagnet at finite temperature using the coherent potential approximation
Authors: Tagüeña-Martínez J. , Sansores L. E. , Elliott R. J.
Published: February 2003

A method developed originally for the insulating Heisenberg ferromagnet with S=1/2 [1] has been extended to the antiferromagnetic case. This method provides the response function at finite T using an ’’alloy analogy’’ in which the system is regarded as an array of spins with Sz=±1/2. The Green’s function have been determined using the coherent potential approximation following the lines for treating dilute systems at T=0 [2] and considering the crystal as an array of uncorrelated bonds [3]. The relation between T and the concentration of ’’wrong spins’’ at T=0 is found from a sum rule for the self-correlation functions. It turns out that the critical temperture TN is the same as the RPA result. The description is reasonable for the spin wave response at T?TN, although it is not correct in the low T limit.
Abstract: Exact results for the quantum Heisenberg chain near T=0
Authors: Stuart Ken , Reiter George
Published: February 2003

The Holstein Primakoff theory is adapted for the calculation of static and dynamic correlation functions in the Heisenberg chain, for arbitrary spin. (AIP)
Ultrasonic studies below Tc in amorphous rare earth-iron alloys
Authors: Hathaway K. , Melamud M. , Cullen J. , Blessing G.
Published: February 2003

Measurements of the velocity of sound as a function of magnetic field are presented for amorphous DyFe2 and HoFe2. The samples were prepared by rapid sputtering. Measurements were taken over a series of temperatures from above to well below the magnetic transition temperatures of both specimens. In DyFe2 shear waves polarized parallel to the field were observed to propagate more slowly than those polarized perpendicular to it. The velocity difference increased with decreasing temperature below the transition temperature becoming one percent of the velocity at sixty percent of the transition temperature. No such mode splitting was observed in HoFe2 down to seventy percent of its transition temperature. Comparison is made with a similar room temperature measurement in a-TbFe2 and with magnetostriction measurements.
On the nature of perpendicular anisotropy in sputtered GdCo thin films
Authors: Herd S. R.
Published: February 2003

The development of perpendicular anisotropy in amorphous GdCo based alloys is still not clearly understood, since no single model has been able to explain all of the various experimental results. This paper presents evidence that links the perpendicular magnetic anisotropy (Ku) in sputtered films with phase separation on a 25Å to 35Å scale as a function of bias. High resolution electron microscopy, large and small angle scattering by electrons, and Lorentz microscopy were combined in this study. Analogous to annealing E-beam evaporated pure GdCo in UHV [Herd, J. Appl. Phys. 49, (1978) 1744], the void network is seen to disappear at −50V bias. With a drop of the compensation point below room temperature, large perpendicular domains are observed at −100V bias, comparable to the development of Ku after the glass transition in evaporated and annealed films. Further increases of bias to −200V led to a decrease in strip width to 0.25μ. Application of bias in sputter deposition is seen to cause a continuous shift towards Co richer compositions, and simultaneously to effect annealing at increasing temperatures during deposition. Anisotropically shaped Co-rich clusters are thought to be the source of perpendicular anisotropy in GdCo based alloys in general. Some recent results on peak shape in diffraction patterns and argon incorporation into sputtered films are discussed.
Atomic diffusion in amorphous Gd-Fe thin films
Authors: Gill H. S. , Judy J. H.
Published: February 2003

We have investigated atomic diffusion in RF-sputtered amorphous Gd-Fe thin films using Auger Electron Spectroscopy (AES). Polycrystalline Co films were deposited in-situ on amorphous Gd-Fe films. These bilayer films were vacuum annealed to induce atomic diffusion of Co into the amorphous Gd-Fe films. AES depth profiles were used to calculate diffusion lengths (Data)1/2 where ta is the annealing time, Da is the diffusion coefficient Daoexp(−Qa/KT), and Qa is the activation energy. We found that Dao=10−3cm2/sec and Qa=1.3 eV suggesting that amorphous Gd-Fe films behave like a liquid phase. Diffusion lengths of 150–250 Å were determined after annealing at 200–300°C for 3 hours. These results suggest that amorphous Gd-Fe films are porous. In agreement, AES depth profiles show that amorphous Gd-Fe films exposed to air possess an oxide surface layer 500–1000 Å thick. Electron diffraction studies showed that the outer halo becomes very sharp after annealing at 300°C for 3 hours. Dark-field microscopy showed that inner halo is still due to an amorphous matrix. However, according to x-ray microanalysis, the outer halo is associated with microcrystallization of Fe. According to our diffusion studies, such an amorphous phase separation can easily develop during sputter-induced surface diffusion to produce perpendicular magnetic anisotropy.
The magnetic properties of Fe-Co amorphous ribbons in low fields
Authors: Kuo Y. C. , Li C. F. , Mai L. M. , Chang W. M.
Published: February 2003

The initial permeability μi and loss factor tanδ of amorphous Fe-Co ribbons of low magnetostriction were measured at room temperature in the high frequency region from 1 kHz to 1000 kHz; the variation of μi at 10 kHz with T was also measured from room T to 300 °C. The initial permeability of as-prepared Fe5Co73Si8B14 ribbons at room T was observed to be about 600 from 1 kHz up to 500 kHz, and then to fall off. The loss factor tanδ was rather small at low frequencies and increased rapidly from about 100 kHz and above. At 500 kHz, its value went up to 0.32. An irreversible T dependence of μi from room T to 300 °C and a disaccommodation-like behavior of μi with time were observed.
Magnetostriction of ribbon-form amorphous and crystalline ferromagnetic alloys
Authors: Tsuya N. , Arai K. I.
Published: February 2003

By rapid quenching methods, ribbon-form Sendust alloys, silicon-iron ribbons Fe100−xSix (4 wt%<x<10 wt%) in the crystalline state as well as iron-boron and iron-cobalt-silicon-boron ribbons in the amorphous state were prepared. All of the ribbons obtained were remarkably flexible. The magnetostriction constant became zero at about the composition Fe92.5Si7.5 and Fe84.74Si 9.71Al5.55. The coercive force Hc and the initial permeability μi in a Sendust straight ribbon with Fe84.9Si9.62Al5.48 were 24 mOe and 30000 respectively after annealing. The magnetostriction constants in Fe100−xBx amorphous ribbons became larger by annealing at 300°C for 3 hours in Ar atmosphere and reached 49×10−6 at x=12.
Magnetic anisotropy in manganese silicide
Authors: Guy C. N. , Strom-Olsen J. O.
Published: February 2003

Torque measurements have been made on a single crystal of MnSi to investigate the way the magnetic field-driven transition from antiferromagnetism (AFM) to ferromagnetism (FM) is effected. The results show the transition to be more complicated than hitherto believed.
Spin reorientations in single crystal HoAl2
Authors: Williams C. M. , Koon N. C. , Das B. N.
Published: February 2003

Torque measurements have been performed on single crystal HoAl2 compound in order to examine the origin of the 20 K specific heat anomaly that occurs in polycrystalline HoAl2. The experimental results indicate the anomaly is due to a spin reorientation between the [110] and [100] in the (100) plane as the temperature is increased. Crystal field calculations suggest the transition should be of the first order; however, torque measurements show that the transition takes place continuously over a finite temperature range.
Permeability, magnetomechanical coupling and magnetostriction in grain-oriented rare earth–iron alloys
Authors: Savage H. T. , Abbundi R. , Clark A. E. , McMasters O. D.
Published: February 2003

Grain-oriented samples of highly magnetostrictive rare earth–iron compounds have been prepared. These samples possess lower inhomogeneous strains than found in the random polycrystalline RFe2 compounds, resulting in much higher values of relative permeability (μr) and magnetomechanical coupling (k33). A partially oriented Th.20Dy.22Ho.58Fe1.95 sample was prepared using a pyrolytic Bridgman type boron nitride crucible. At a bias field of 100 Oe k33=.73, which is considerably larger than found in the random polycrystal of the same composition. A relative permeability of 36 occurs in this same sample when a low ac drive of 1.6 Oe rms is used. A second fabrication method using a horizontal zone technique with a supporting ’’cold finger’’ was employed to grow the ternary Tb.27 Dy.73Fe1.98. The low ac drive values of k33 and μr were .74 and 19 respectively. The permeability at low bias was found to possess a sharp ac drive dependence. Near zero bias, when the drive was changed from 1.6 Oe rms to 13 Oe rms, μr in the quaternary increased from 36 to 98. In the ternary the values of μr near zero bias increased from 19 to 61. Magnetostriction measurements on both samples show a significant increase in dλ/dH and λs over the random polycrystals.
Exchange magnetostriction in the paramagnetic phase of EuS
Authors: Yacovitch R. D. , Shapira Y. , Foner S. , McNiff E. J.
Published: February 2003

The longitudinal and transverse magnetostriction in EuS were measured at 1.8<T<146 K, in magnetic fields up to 130 kOe. In the paramagnetic phase (T≳Tc=16.49 K) the magnetostriction is predominantly due to the strain dependence of the exchange energy. The results are explained in terms of the theory of Callen and Callen supplemented by numerical calculations of the nearest-neighbor and next-nearest-neighbor two-spin correlation functions. The agreement with theory is good, but small deviations near Tc suggest that EuS departs from the ideal Heisenberg model.
Magneto-elastic coupling by dipolar interactions : Spin orientation in MnO
Authors: Bidaux R. , Conte R. , Nasser J. A.
Published: February 2003

MnO is a low temperature antiferromagnet in which a spin orientation anisotropy within the plane of easy magnetization has been observed experimentally. The microscopic origin of this anisotropy has not yet been elucidated. As a consequence there is a certain uncertainty in the determination of the magnetic structure and in the interpretation of the magnon spectrum. We show here that magneto-elastic coupling by dipolar interactions leads to well defined anisotropy axis which are determined to be the [1, 1̄, 0] directions modulo 2π/3. We have calculated the values of coupling coefficients which are derivatives of the components of the dipolar tensor with respect to the components of the strain tensor. Moreover using the mechanism proposed in this paper it should be possible to interpret correctly the magnetic properties of MnO in presence of external fields (magnetic field and mechanical stresses).
Magnetic properties of an amorphous antiferromagnet
Authors: Walstedt R. E. , Kummer R. B. , Geschwind S. , Narayanamurti V. , Devlin G. E.
Published: February 2003

We present measurements and a theoretical analysis of the magnetic properties of dilute neutral (In) donors in CdS, which we demonstrate to be a well-characterized example of an amorphous antiferromagnet with spins S=1/2. High-quality data for relative values of sample magnetization have been obtained by the Faraday rotation method at temperatures ranging from 55 mK to 2.5 K and fields up to 15 kG. Data are given for crystals with neutral donor concentrations of 8⋅1016/cm3 and 2.1⋅1017/cm3. The susceptibility, χ, increases monotonically with decreasing T with no evidence of ordering, even though the median exchange coupling is ∼7 K. A model Hamiltonian is derived by scaling calculations of direct exchange for the H2 molecule to the Bohr radius and effective Rydberg of the donor wave functions. A sample of such a Hamiltonian is generated in a computer simulation and solved approximately by dividing the system into clusters (and isolated spins) according to a coupling threshold and solving the cluster Hamiltonians exactly. Inter-cluster interactions are included in a molecular field approximation. Excellent agreement with experiment is found, and χ is shown to be dominated by clusters, both even and odd, at all temperatures.
Annealing effects in Ni-based amorphous alloys with dilute concentrations of Fe
Authors: Prater J. T. , Egami T.
Published: February 2003

The melt-spun amorphous FecNi80−c P14B6 alloys show spin-glass behavior for c?5, and mictomagnetic behavior for 5<c<∼10. We show that spin-glass behavior is insensitive to annealing treatments below 300° C, which is well below temperatures that produce crystallization. The mictomagnetic alloys are slightly influenced by such treatments. This result suggests a long-range nature for the magnetic interactions in the spin-glass state. Annealing at 350° C results in the appearance of ferromagnetism, without obvious devitrification. The exact nature of this transformation is still not known.
Ultrasonic measurement of the critical exponent α′ for the spin glass CuMn
Authors: Hawkins G. F. , Thomas R. L. , de Graafa) A. M.
Published: February 2003

Ultrasonic measurements are presented providing the first direct measurement of the critical exponent α′ for the spin glass CuMn. We find α′=−1.9±0.2 for a sample containing 5 at. % Mn.
Anomalous magnetoresistance in AuFe spin glass
Authors: Nigam A. K. , Majumdar A. K.
Published: February 2003

Transverse magnetoresistance has been measured in AuFe polycrystals betweem 2.5 K and 300 K in magnetic fields up to 18 KG. For a sample with 2.9 at. % Fe (T0=16 K) the magnetoresistance at low temperature first increases with the field, peaks at around 1 KG and then decreases. The peak height decreases rapidly with increasing temperature. At temperatures above 6 K there is no measurable positive magnetoresistance even at 50 gauss. The negative component above 2 KG varies roughly as (Δρ/ρ) = −a(T) Bn with n=1.9±0.1. The amplitude a(T) saturates at low temperatures (2.5 K<T<8 K) and then falls off gradually with temperature. At around 125 K the negative component becomes undetectable. While no explanation could be found for the behaviour of the positive magnetoresistance, the negative one could be qualitatively explained in terms of the spin-disorder scattering and the freezing of the spins below T0. The alloys with higher Fe content (6.6, 10, 13, 18 at. % Fe) show that the magnetoresistance between 77 K and 300 K is negative but the field and the temperature dependence of (Δρ/ρ) changes significantly as one passes through the spin glass, mictomagnetic and inhomogeneous ferromagnetic regimes.
New magnetic properties of a dilute spin-glass
Authors: Holtzberg F. , Tholence J. L. , Godfrin H. , Tournier R.
Published: February 2003

The insulating Sr1−xEuxS system exhibits spin-glass properties for x≳0.05 due to competing ferro and antiferromagnetic interactions. A scaling law x/Tf=f (ln ν) represents the frequency (ν) dependence of Tf, the temperature of the maximum of χa.c. (or spin-glass freezing temperature). This frequency dependence of Tf is at least an order of magnitude bigger than in a canonical spin-glass such as AuFe. The dipolar interaction is responsible for the anisotropy inside magnetic clusters. For x<0.05 the a.c. susceptibility, χa.c., doesn’t exhibit a single maximum, but after an initial maximum or plateau around Tp it increases to a second rounded maximum, at much lower temperatures. Below Tp, which is concentration independent, a remanent magnetization appears proportional to x2. Furthermore, at this temperature deviations from a Curie law of χa.c. increase more rapidly than x. Moreover, the frequency dependence of Tp permits a determination of a blocking energy. This energy is in agreement with the anisotropy barrier due to the dipolar interaction for a ferromagnetic pair of first neighbors. All these results support the idea of short range order for individual pairs, and small magnetic clusters which are blocked below Tp on random anisotropy directions determined by the intra-cluster dipolar interaction. A similar change in the magnetic properties of other spin-glasses is expected.
Magnetic susceptibility of NaxV2O5−β
Authors: Schlenker C. , Buder R. , Nguyen V. D. , Dumas J. , Friederich A. , Kaplan D. , Sol N.
Published: February 2003

The magnetic properties of Nax V2 O5−β vanadium bronzes have been studied on single crystals with x=0.20, 0.30 and 0.33. Curie behaviour has been found for all samples. For x=0.33, a magnetic transition takes place at T1?18 K. The initial reversible susceptibility, thermoremanent and isothermal remanent magnetizations have been measured at T<18 K for different crystallographic orientations. The data suggest an antiferromagnetic behaviour with the direction of antiferromagnetism perpendicular to the b↘-monoclinic axis. The remanent magnetizations are compared to a spin glass behaviour due to a possible position disorder of the V4+. It is also proposed that there could be a weak ferromagnetism along the b↘-axis.
Magnetization of glassy Co-B alloys
Authors: Hasegawa R. , Ray R.
Published: February 2003

By using a chill-casting technique, binary Co100−xBx alloys have been made for the boron content x between 10 and 31. The alloys with 14 ?x?29 are found to be noncrystalline, others being partially crystalline. The saturation magnetic moment per Co atom varies linearly from 1.49 μB at x=14 to 0.98 μB at x=29. At x=25, we find μs=1.09 μB which is close to μs=1.11 μB for the crystalline Co3B. The ferromagnetic Curie temperature, ϑf, is above the crystallization temperature of the material for x < 27 and is estimated to vary from about 780 K for x=22 to 670 K for x=29, giving a value of ϑf = 725 K for x=25. This value is close to ϑf = 747 K for the crystalline Co3B. Other evidence is given that the magnetic properties of glassy Co-B alloys differ very little from those of the crystalline counterparts, being quite different from the glassy Fe-B case reported previously.
Magnetic exchange between Ti3+ ions in titanium phosphate glass
Authors: Perry C. H. , Kinser D. L. , Wilson L. K. , Vaughn J. G.
Published: February 2003

Magnetic properties of reduced titanium phosphate glasses are reported. Magnetic susceptibility measurements from 1.0° to 400°K indicates behavior typical for amorphous antiferromagnetism. The more reduced glasses show an anomalous field dependence in the susceptibility suggestive of ferromagnetism. A microstructural model for the glasses is developed from physical, chemical and magnetic data. Using the model, a theoretical magnetic susceptibility equation is derived. The equation includes contributions to a total susceptibility from isolated Ti(3+) ions and ion pairs which participate in exchange. From electron spin resonance results, the theoretical susceptibility equation and the experimental Ti(3+) ion concentration in the glasses, a good fit to the experimental magnetic susceptibility data is obtained. Results from the theoretical equation indicates that ferromagnetic and antiferromagnetic interaction between exchange-coupled Ti(3+) ions may occur. At low temperatures a downward curve toward the origin of the inverse susceptibility is predicted which is consistent with the experimental data.
The influence of carbon on the hyperfine interaction and Curie temperatures of amorphous Fe84B16−xCx*
Authors: Musser D. , Chien C. L. , Luborsky F. E. , Walter J. L.
Published: February 2003

Amorphous Fe84B16−xCx (0?x?10) have been studied by 57Fe Mössbauer spectroscopy. The Curie temperature (TC) increases monotonically with carbon concentration. Well-defined hyperfine field distributions {P(H) } at 4.2 K have been found. The distribution width as well as the asymmetry of P(H) increase smoothly as carbon replaces boron. The mean hyperfine field and the average iron moment are found to be proportional. There is a small change in the temperature dependence of the reduced hyperfine field as the carbon concentration increases. This suggests the distribution width of the exchange interactions varies slightly with carbon concentration.
Temperature dependence of the magnetization in amorphous alloys
Authors: Bhagat S. M. , Spano M. L. , Rao K. V.
Published: February 2003

We have used ferromagnetic resonance to measure the temperature dependence of the saturation magnetization in three glassy alloys: I: Fe29Ni49P14B6Si2 (Metglas 2826B), II: (Fe0.4Ni0,6)75P16B6Al3, and III: (Fe0.5Ni0.5)75P16B6Al3. In I we find that, for 4 ?T?300 K, the magnetization follows the relaxation M(T) =M0(1–BT3/2 −CT5/2) with B and C values fairly close to those obtained using Mössbauer and vibrating sample magnetometer techniques. For II and III it is necessary to include the effects of spin wave energy renormalization, with temperature, to account for the variation of M over a comparable temperature regime. That is, the parameter B obeys the relation: B(T) =B0[1/(1−αT5/2)]3/2. In terms of the spin wave stiffness this implies D=D0[1−β (T/Tc)5/2] meV-Å2 where, again, the parameter values are in the range found for similar systems by neutron scattering.
Abstract: Annealing behavior of amorphous ferromagnetic Co-Fe-B and Fe-B thin films
Authors: Gangulee A. , Aboaf J. A. , Kobliska R. J.
Published: February 2003

The annealing behavior of amorphous Co-Fe-B and Fe-B thin films, fabricated by RF sputtering in an Ar plasma, has been investigated. (AIP)
Magnetic aftereffect due to domain wall motion in amorphous Tb-Fe sputtered films
Authors: Ohashi K. , Takagi H. , Tsunashima S. , Uchiyama S. , Fujii T.
Published: February 2003

A very large aftereffect is observed in sputtered amorphous Tb-Fe films with uniaxial anisotropy perpendicular to the film plane. In the present experiment, the film is first saturated to −Ms by a premagnetizing field Hp (<0), where Ms is the saturation magnetization. Then the applied field is suddenly changed from Hp (<0) to Ha (?0) which is close to the coercive field. With proper choice of the film composition, temperature, Ha and so on, the magnetization changes from −Ms to almost +Ms with the passage of time while Ha is kept constant. The dependences of the aftereffect on the applied field and on the temperature are shown. The domain observation by means of polar Kerr effect reveals that the aftereffect is associated with the slow dendritic growth of the magnetic domains. It is also found that the density of reversed domain nuclei depends on the premagnetizing field Hp.
Anomalous resonance field shifts in amorphous Gd.37Al.63
Authors: Hart S. C. , Wigen P. E. , Malozemoff A. P.
Published: February 2003

An anomalous frequency independent magnetic resonance field shift has been observed in amorphous Gd.37Al.63 thin film alloy. Data are reported at frequencies of 9.2, 23.0, and 34.9 GHz and over a range of temperature from 4.2 K to 100 K. Below about 50 K the magnitude of the applied field required for resonance begins to deviate significantly from the value expected from the bulk magnetization of the amorphous material. An increase in the linewidth of nearly the same magnitude as the deviation of the ’’internal field’’ is also observed. The magnitude of the resonance field shift and the change in the linewidth are both insensitive to changes in the operating frequency. It is proposed that the observed resonance field shifts can be attributed to the excitation of spinwave modes localized or ’’pinned’’ within small ferromagnetic regions. The observed increase in the linewidth is then explained within the framework of this model as being due to changes in the demagnetizing fields associated with each of the variously shaped ferromagnetic clusters.
Inhomogeneities and FMR spectra in some D.C. sputtered amorphous Gd-Co films
Authors: Prasad Shiva , Krishnan R. , Suran G. , Sztern J. , Jouve H. , Meyer R.
Published: February 2003

FMR technique has been shown to be capable of detecting chemical inhomogeneities present in some amorphous GdCo films. A group of bulk modes observed when the polarizing field is perpendicular to the film plane, have been shown to correspond to absorption from regions which differ slightly in their magnetization and hence in their relative Gd or Co concentration. Such inhomogeneities seem to increase with the bias voltage. A typical result shows that Gd concentration variation is in the range 1–2 at.% and which is beyond any chemical analysis used currently. These inhomogeneities increase with the bias voltage and are distributed, as it were, in the whole volume of the film in a random manner as shown by acid etching experiments. Vacuum annealing at T up to 290°C does not lead to any homogenization and argon anneal leads to a new situation with a very large in plane anisotropy besides a spin wave spectra now appears in all the samples.
Influence of the magnetomechanical pole-effect on the behavior of thin vibrating reeds
Authors: Berry B. S. , Pritchet W. C.
Published: February 2003

It is demonstrated that the vibration frequencies of a magnetized reed can be sensibly affected by a magnetic field, due to the restoring force exerted on the moving pole. A simplified theory of this effect is developed which gives reasonable agreement with experimental observations. The relative importance of the pole-effect depends on the geometry of the reed and increases with the ratio of length to thickness. The effect decreases rapidly for higher overtones. Unlike the magnetization, the pole-effect does not saturate but rather increases steadily in post-saturation fields, where it is conveniently separated from the ΔE-effect on which it is generally superimposed. For the geometries typically employed in the investigation of liquid-quenched amorphous alloys, the pole-effect can be large for the fundamental mode and may be used to determine the temperature dependence of the magnetization. If unrecognized, on the other hand, the pole-effect can cause anomalies in the magnitude of the apparent elastic constant, and especially in the temperature dependence exhibited in the vicinity of the Curie point.
Magnetostriction of Fe100−xBx glasses
Authors: O’Handley R. C. , Narasimhan M. C. , Sullivan M. O.
Published: February 2003

Magnetostriction λs has been measured at room temperature and 80 K in Fe100−xBx (14?x?23 at.%) glasses using metal foil strain gauges. Several compositions were also studied as a function of temperature from 80 K to T ? TC. The single-ion uniaxial temperature dependence confirmed previously for Fe80B20 glass is also observed here for x=20 and 22. At lower boron concentrations departures from this expected temperature dependence are observed. The values of λs(295K) show a broad maximum of about 35×10−6 at x?20 at.%B. Crystallization of the glasses gives rise to a nonmonotonic temperature dependence of λs.
Studies of chemiluminescence accompanying fluorine atom etching of silicon
Authors: Donnelly Vincent M. , Flamm Daniel L.
Published: February 2003

A broad continuum centered at 632 nm is present during the etching of silicon by F atoms, and in the flowing afterglow of an SiF4 discharge. A study of this feature and other spectra in pulsed and continuous discharges provides strong evidence that SiFx radicals (apparently SiF2) are formed as primary products when Si is gasified by atomic fluorine. The 632-nm emission is tentatively ascribed to the reaction processes (1) SiF2+F (or F2) → SiF*3 and (2) SiF*3  → SiF3+hνcontinuum.
Stability of cable-in-conduit superconductors
Authors: Lue J. W. , Miller J. R. , Dresner L.
Published: February 2003

The stability margin of a single triplex of NbTi/Cu strands soldered around a heater wire, sheathed in a stainless-steel tube, and cooled by pressurized helium is found to be multivalued for certain combinations of transport current, ambient helium pressure, and externally imposed helium flow. A qualitative model based on the idea that good recovery in stagnant or slowly flowing helium is due to heating-induced flow accounts well for the complex multivalued behavior of the stability margin.
Augmentation of heat and mass transfer in laminar flow of suspensions: A correlation of data
Authors: Ahuja Avtar S.
Published: February 2003

The experimental data from literature on the augmentation of heat and gas transport in the laminar flow of suspensions of polystyrene spheres have been correlated on common coordinates. The correlation includes the influences of particle size, tube diameter and length, shear rate of flow, transport properties of diffusing species (heat or gas) in suspending liquids, and of the particle interactions on the augmentation of heat or gas transfer in flowing suspensions.
On the possibility of decrease of bending moments in circular coils of toroidal magnets
Authors: Keilin V. E. , Shleifman V. Kh.
Published: February 2003

It is shown that (1) if an angular dimension of the supporting structure is large enough, the so-called modified D-shaped coil of toroidal magnet differs slightly from the circular one, (2) with the increase of support angle maximum bending moment in a circular toroidal field coil diminishes rapidly. Thus the realistic choice of support angle can guarantee practically pure tension in circular toroidal field coils.
Behavior of edge-grown low-capacitance superconducting tunnel junctions
Authors: Dousselin G. , Rosenblatt J.
Published: February 2003

By growing the oxide barrier on the edge of a thin film rather than on its flat surface, we have succeeded in obtaining small-area tunnel junctions. The fabrication process suitable for integration of many elements in small circuits is described. Supercurrent response to magnetic and microwave fields unambiguously characterize the Josephson behavior of these junctions.
Two-photon resonant four-wave parametric amplification
Authors: Dutta Niloy K.
Published: February 2003

Four-wave parametric amplification is discussed when the incident pump frequency is close to a two-photon resonant transition in the material. Expressions for the amplification factor are obtained both under steady-state and pulsed excitation and also for a nonmonochromatic pump. For ultrashort-pulse excitation an ’’energy theorem’’ is derived and discussed. In steady state, expressions for optimum frequency and intensity are obtained. The amplification factor under broad-band excitation decreases with increasing pump linewidth.