bluuebunny/crossref_metadata_2025 huggingface dataset:
Effect of nucleating agents on YIG crystallization in Na2O–SiO2–Y2O3–Fe2O3 glass system
Authors: Bahadur D. , Das P. K. , Chakravorty D.
Published: February 2003

The effect of nucleating agents such as 2 mole % of P2O5 or TiO2 on the crystallization of yttrium iron garnet in Na2O–SiO2–Y2O3–Fe2O3 glass system has been studied using x-ray diffraction, Differential Thermal Analysis (DTA), magnetization measurements, and optical microscopy. Each glass was given a two-stage heat treatment before being investigated. X-ray diffractograms of all the heat-treated samples show the presence of YIG as well as another magnetic crystalline phase. Magnetization studies confirm the presence of two magnetic phases. Magnetization and x-ray data indicate that P2O5 is a better nucleating agent than TiO2. Optical micrographs also show a fine and homogeneous grain distribution for the sample containing these nucleating agents.
A study of the free energy surface of an Ising spin glass
Authors: Soukoulis C. M. , Grest G. S. , Levin K.
Published: February 2003

We study the free energy surface of a mean field model for a spin glass in a field H. We obtain field cooled and zero field cooled magnetizations that look qualitatively like experiment. The field cooled state which has the lowest free energy of any state we generated, satisfies Maxwell’s relations. All states obtained by cooling have reversible properties (in the absence of relaxation effects). By contrast, any change in H below the glass transition leads to irreversibility (minima hopping), except at very large H. We have calculated hysteresis loops which compare favorably with experiment for a variety of situations and make predictions for additional hysteretic effects.
Explanation of the freezing temperature in spin glasses
Authors: Morgenstern I.
Published: February 2003

The freezing of spins in the two-dimensional ±J-model [1,2] (anti- and ferromagnetic nearest neighbour bonds between Ising spins) is investigated for the case of a one-spin-flip-dynamic (as used in Monte-Carlo calculations). The phenomenon is caused by the existence of finite energy barriers between the different ground-state valleys. The barrier heights are calculated by a numerical method turning one ground state to its inverse. The freezing temperature is determined by the vanishing of the free energy barriers between the valleys. The corresponding entropy is calculated by the Transfermatrix-Method. The free energy barriers vanish at Tf≂1.3±0.1 in good agreement with the cusp of the susceptibility in Monte-Carlo calculations. The long-time behaviour of spin glasses is governed by the mentioned free energy barriers.
dc magnetization in some A
g Mn spin glasses
Authors: McAlister S. P. , Freeman M. R.
Published: February 2003

We report dc magnetization measurements on 3 Ag Mn spin glasses where we field-cool the samples into the spin-glass state, then rotate the sample through 90°. In this way we measure the so-called clamped magnetization as a function of both field and temperature. We discuss the results in terms of the anisotropies in the spin glass and a simple two-level model.
Investigation on the magnetically diluted spinels CdIn2-2xCr2xS4
Authors: Nogues M. , Saifi A. , Hamedoun M. , Dormann J. L. , Malmanche A. , Fiorani D. , Viticoli S.
Published: February 2003

The cation distribution of the solid solution CdCr2xIn2-2xS4, was determined by Mössbauer spectroscopy on 57Fe doped samples. At high temperature the susceptibility follows a Curie-Weiss law. The low temperature field dependence of the magnetization shows that the samples 0.90≤x≤0.98 are ferromagnetic. In the range 0.25≤x≤0.98, irreversible behaviour, remanent and time dependent magnetization are observed. Magnetization and EPR results on the sample x=0.60 are consistent with the spin glass behaviour found by dc susceptibility measurements.
Electron–phonon scattering in valence fluctuators
Authors: Cox Daniel L. , Wilkins John W.
Published: February 2003

The phonon-induced scattering rates in metals are calculated as a function of the electronic energy for the case where the electron states are those formed from conduction levels hybridized with localized f levels and where either acoustic or optic phonons may be involved. Accordingly these rates are appropriate for some theoretical models of valence fluctuators. The hybridization produces not only a broadening of the unhybridized rates but also zeros in the rates. The mechanism for these zeros is connected with that of Fano antiresonances.
Observed and calculated magnetic properties of the double helimagnetic compounds La2FexMn2−xS5
Authors: Plumier R. , Sougi M. , Lecomte M.
Published: February 2003

In the orthorhombic compounds of the series La2FexMn2−xS5, the magnetic ions are located on distorted octahedral and tetrahedral sites which alternate on zigzag chains parallel to [001]. The observed magnetic structures indicated that, in these compounds with TN≂88.5 K, strong antiferromagnetic interactions J1 and J2 exist between first nearest neighbors (n.n.) of the same type aligned on a zigzag chain as well as J between first n.n. of different type on a chain. High precision magnetic susceptibilities have just been determined in the temperature range 4–300 K on some powdered specimens of the series. To explain the observed results, the theoretical derivations of TN, the perpendicular susceptibility, and pitch angle have been performed in the case of two types of magnetic ions acted on by unequal molecular fields. A definite set of J, J1, and J2 exists which gives a satisfactory agreement between these calculated values and the measurements as shown in the case of La2Fe1.5Mn0.5S5.
Mössbauer study of magnetism in an amorphous Fe40B60 sputtered film
Authors: Blum N. A.
Published: February 2003

Mössbauer studies of amorphous iron/boron alloys have proved useful for understanding magnetic phenomena in structurally disordered systems. In iron-rich alloys the 57Fe Mössbauer spectra at T≪TC of both melt-quenched and sputtered materials consist of broadened magnetic hyperfine lines, indicative of structural distortions in the compounds Fe2B and Fe3B. The spectra of sputtered films with approximately 50% Fe may be characterized by two qualitatively distinct Fe sites: (1) sites yielding a broadened magnetic hyperfine spectrum similar to the sharp spectrum of the compound FeB, and (2) sites having a zero (or very small) magnetic hyperfine field, evidenced by a slightly asymmetric, partially resolved, quadrupole doublet. In order to further examine the nature of these low field sites, a 40% Fe sputtered amorphous film was examined at 4.2 K in external magnetic fields up to 8.0 T. Interpretation is difficult, partly because the magnetic and quadrupole interactions are of comparable magnitude and partly because of the distributed nature of the hyperfine parameters. A pure spin-glass phase was ruled out by a narrowing of the spectrum in a 2.0 T external magnetic field. Two components were identified in the external magnetic field spectra: (1) nonmagnetic (∼50%), and (2) magnetic, with unusual behavior that may be due to a low-moment, mixed ferromagnetic/spin-glass phase.
Mössbauer spectroscopy of amorphous Fe–Si–B alloys with different free volume content
Authors: Allia P. , Ferro Milone A. , Vinai F. , Fratucello G. , Ronconi F.
Published: February 2003

The hyperfine field distributions of as-cast and annealed Fe81.5Si4B14.5 amorphous alloys prepared with different quenching rates have been measured at room temperature by means of Mössbauer spectroscopy. No significant differences have been found between the spectra of as-cast materials produced at different quenching rates, in contrast with the results of measurements of the electrical resistivity and the magnetic permeability aftereffect. This result indicates that the variation of the distribution of pressure–density fluctuations in differently quenched systems does not modify the value of the hyperfine field, which is rather dominated by the effect of the local magnetic disorder, and not substantially influenced by small variations of the quenching rate. The hyperfine field distributions of annealed ribbons are coherently shifted towards higher values with respect to the ones of as-cast alloys. This result is related the increase of the Curie temperature, observed in these alloys after annealing, and is interpreted as the effect of the irreversible reduction of the local magnetic disorder induced by structural relaxation.
Amorphous FexNb100−x with wide composition range*
Authors: Chien C. L. , Unruh K. M. , Liou S. H.
Published: February 2003

Sputtered amorphous FexNb100−x (30≤x≤85) has been studied by Mössbauer spectroscopy and resistivity measurements. The samples with x<60 are nonmagnetic. The magnetic ordering temperatures of the samples with x≥60 increase with Fe content. Small magnetic hyperfine fields are observed in the magnetic samples, consistent with the small Fe moments measured. The resistivity of the magnetic and nonmagnetic samples show different temperature dependences. Only the magnetic samples exhibit a resistivity minimum, indicating a Kondo-like mechanism.
Characteristics of Co–B–Si glasses from magnetization measurement
Authors: Maszkiewicz M.
Published: February 2003

The spin wave stiffness constant D was determined from the temperature dependence of the magnetization for Co–B–Si glasses in the range 70% Co to 80% Co. We found that: (a) varying the amount of Si has a strong effect on D, (b) introducing Si into Co–B initially increases D (which may be interpreted as an increase of atomic order) with a maximum for about 5% Si and then decreases for larger amounts up to 15% Si, (c) most of our samples have a dependence of D on the Curie temperature TC for varying composition similar to that of the Fe–Ni–B–P glasses; however, three samples have dependence similar to that of Co–X glasses (X=P+B or P), (d) the decrease of magnetization with T can be described well, for most of investigated Co–B–Si samples, by a Heisenberg model with short-range interaction.
Low temperature specific heat and electrical resistivity of amorphous Ni–B alloys
Authors: Motsay R. , Wang L. Q. , Onn David G. , Donald I. W. , Davies H. A.
Published: February 2003

The specific heat of Ni100−xBx amorphous alloys with x=18, 32, 36, and 40 is determined from 0.7 K to 40 K, and compared with results for Ni80P14B6 and Ni–P alloys. The electronic contribution (γT) decreases rapidly for the Ni–B alloys as the B concentration increases and as P replaces B near the Ni80M20 composition. The temperature dependence of the Debye temperature is obtained up to 40 K. For Ni82B18, the Debye temperature is in good agreement with the value obtained from the temperature dependence of the electrical resistivity (ρ/ρ300). (ρ/ρ300) was measured for all four alloys. The magnetic specific heat CM, which is almost temperature independent, is attributed to ferromagnetic clusters in these paramagnetic alloys.
Crystallization of (Fe1−xNix)80B20 amorphous alloys
Authors: Orehotsky J. , Rowlands Camille
Published: February 2003

The crystallization behavior of a Fe60Ni20B20 amorphous ribbon alloy was investigated by isothermal resistivity measurements and by x-ray diffraction transmission pin-hole techniques. The resistivity decreased appreciably (∼25%) upon crystallization. The time dependence of the resistivity at various isothermal crystallization temperatures displayed a prominent kink indicative of a two stage crystallization process where about 80% of the resistance loss is associated with the first crystallization stage. An activation energy of 85 kcal/mole was found to characterize the kinetics of the first crystallization stage. The x-ray results failed to reveal unambiguously the structural changes suspected to accompany the advent of the second crystallization stage. A comparison of the crystallization results of this study where nickel replaces iron with the results of a previous study where phosphorus replaces boron in the Fe80B20 stoichiometry revealed numerous systematic differences in behavior. An analysis of crystallization in a Fe20Ni60B20 amorphous alloy was hampered by a small apparent resistivity change which prevented an accurate evaluation of the kinetic behavior.
Computer simulation study of the classical xy-chain in a magnetic field *
Authors: Gerling R. W. , Landau D. P.
Published: February 2003

Results are presented for the static and dynamic behavior of a classical XY-chain in a magnetic field. Equilibrium configurations were produced by an importance sampling Monte Carlo method. Static properties are evaluated from these data and a spin-dynamics method is then used to evaluate time displaced correlation functions. The energy-energy correlation function shows a t−1 behavior for times t≳J−1. The correlation function <Sxi(0)Sxi+r(t)≳ decays to the square of the magnetization for large times, and the correlation function <Syi(0)Sy1+r(t)≳ shows oscillatory behavior.
Domain structure and behavior in Fe40Ni40P14B6
Authors: Steck G. J. , Pregger B. A. , Kramer J. J.
Published: February 2003

An experimental investigation was conducted to determine the static and dynamic domain characteristic of the amorphous alloy Fe40Ni40P14B6 both before and after proton irradiation to compare with samples before and after annealing. The as-received samples show the combination of wide wavy slab-like domains, regions of a star-like domain pattern, and a fine domain structure with magnetization normal to the ribbon surface, as has been noted by others. Observation of this domain structure under dynamic magnetization conditions, by means of the Kerr magneto-optic effect, indicated nonreproducibility in the domain pattern from cycle to cycle. Following annealing at 189 °C for 3 1/2 h, with a proton fluence of 5×1015/cm2 at sufficient energy to penetrate through the sample, only straight slab-like domains could be observed. Kerr effect observations of the dynamic domain behavior revealed a high degree of reproducibility from cycle to cycle. This suggests that the nonreproducibility in the as-received samples is most likely due to the residual stresses and defects incorporated into the sample during the melt-spinning operation. The surface roughness of the melt-spun sample probably plays a less important role in the domain reproducibility.
Kinetics of changes in initial permeability produced by magnetic annealing in a zero-magnetostrictive FeCoSiB amorphous alloy
Authors: Jagielinski T.
Published: February 2003

The kinetics of the changes in initial permeability μ produced by magnetic, parallel, and perpendicular field annealing have been measured in a zero-magnetostrictive Fe4.7Co70.3Si15B10 amorphous alloy in the temperature range 320–700 K. The activation energy obtained from μ−1 data is equal to 2.05 eV and is the same as one obtained from direct anisotropy measurements. However, the activation energy obtained from the kinetics of permeability itself is much smaller, in the range 1.05–1.5 eV, and the discrepancy among the published values is explained. There is a proportionality between the μ−1 value and the amount of induced anisotropy, and the proportionality factor depends on the direction of Ku.
Domain walls at high temperatures
Authors: Aharoni Amikam
Published: February 2003

To check the validity of micromagnetics at high temperatures, a one-dimensional domain wall in Fe is computed allowing the magnitude of the magnetization to change locally, according to the molecular-field theory. The result is that the local variations of the magnitude are negligibly small even up to 93% of the Curie temperature.
Measurements on microscopic barium ferrite single crystals using a vibrating reed magnetometer
Authors: Schippan R. , Hempel K. A.
Published: February 2003

The magnetization processes occuring in a small individual particle (dimensions about 4 μm) of a barium ferrite single crystal are investigated using a high sensitivity vibrating reed magnetometer.1,2 With this apparatus magnetic moments smaller than 10−9 A cm2 may be detected if the particle is fixed to a hollow quartz reed which is kept under vacuum. The operating frequency is tuned to the resonance frequency of the reed. The examination exhibits a perfect rectangular primary hysteresis loop which indicates that the magnetic moment of the sample is completely reversed by a single Barkhausen jump. By repeating the reversal, a wide range of jump field strengths is revealed. Two types of minor loops are demonstrated depending on the magnitude of the jump field strength.
Bitter patterns in polarized light: A probe for microfields
Authors: Jones G. A. , Lacey E. T. M. , Puchalska I. B.
Published: February 2003

This paper discusses the observation of Bitter patterns on YIG films made with a polarizing microscope. The local stray field associated with the domain structure induces a birefringence in the colloid which in turn determines the light intensity I transmitted by the analyzer. Under the conditions of fixed crossed polars, if the local field makes an angle ψ with the polarizer then I=k(1−cos 4ψ). The nature of the birefringence and its effect upon the intensity allows, in principle, a directional map of the stray field pattern to be constructed.
Magnetism in transuranics (invited)
Authors: Smith J. L. , Fisk Z.
Published: February 2003

Transuranic materials exhibit all types of magnetic behavior. This behavior is a relatively smooth function of atomic number and of the atomic volume of the atoms in the materials. The systematics are best described in terms of these volumes as a measure of intinerancy, mixed valence, or local moment formation.
Finite-size scaling and phenomenological renormalization (invited)
Authors: Nightingale Peter
Published: February 2003

Research in recent years has shown that combining finite-size scaling theory with the transfer matrix technique yields a powerful tool for the investigation of critical behavior. In particular, the method has been used to study two-dimensional statistical mechanical and one-dimensional quantum mechanical systems. We review finite-size scaling theory from the general point of view of renormalization group theory for both continuous and first-order transitions (both for systems with discrete and continuous symmetries). We review applications where a comparison with exact results can be made. These include the Ising, Baxter, and q-state Potts models and the Ising model with a defect line. Various other applications such as quantum systems, the self-avoiding random walk, percolation, and Kosterlitz-Thouless transitions are briefly reviewed. The Kosterlitz-Thouless transitions and the critical fan in the antiferromagnetic 3-state Potts model are discussed at somewhat greater length.
Specific heat and magnetic susceptibility of the Kondo model
Authors: Andrei N. , Rajan V. T.
Published: February 2003

The recently obtained diagonalization of the Kondo model is used to formulate the thermodynamics of the model in terms of integral equations. These are solved to yield the specific heat and susceptibility as a function of the temperature for different magnetic fields. The curves are compared to the experimental data.
The magnetic equation of state of LiTbpY1−pF4
Authors: Brierley S. K. , Griffin J. A.
Published: February 2003

The magnetic equation of state of the randomly diluted dipolar coupled Ising ferromagnet LiTbpY1−pF4 has been measured over a reduced temperature range of approximately two decades near the critical point using a sensitive SQUID magnetometer. This is the first investigation of the equation of state of a randomly diluted magnetic system at marginal dimensionality (d*=3). Measurements were made at Tb concentrations of p=0.90 and p=0.63 in order to examine the critical behavior for widely differing degrees of dilution. The data have been compared to three different renormalization group (RG) calculations of the equation of state. For both concentrations, a randon nonasymptotic form of the equation of state is found to give the best description of the critical behavior.
Field dependent neutron scattering study of the quasi 2-D Heisenberg antiferromagnet K2MnF4
Authors: de Jongh L. J. , Regnault L. P. , Rossat-Mignod J. , Henry J. Y.
Published: February 2003

The magnetic phase diagram of K2MnF4 has been determined in fields up to 85 kOe. The variation of TC with H is shown to be related to the anisotropy dependence of TC for the 2-d anisotropic Heisenberg model.
Verification of first-order magnetic phase transition in single crystal iron films
Authors: Rachford F. J. , Prinz G. A. , Krebs J. J. , Hathaway K. B.
Published: February 2003

In a recent publication [1] we reported observations of a first order transition of the orientation of the magnetization in single crystal iron films grown on GaAs substrates by molecular beam epitaxy. We have extended our observations of these samples, studying both the magnetization and the ferromagnetic resonance (FMR) in the vicinity of the transition. We find excellent agreement between the observed and the calculated values for the magnetization and the FMR in the transition region using parameters determined from FMR at magnetic fields large enough to quasi-align the magnetization with the applied magnetic field. Hysteresis is noted in both the magnetization and the FMR at the transition verifying the predicted first order nature of the transition. An examination of the FMR lineshape and the component of the magnetization along the [110] direction in the transition region indicate that a small but finite field change is required to propagate the phase transition through the sample. We suggest that this sluggishness is due to domain wall pinning induced by the presence of strain-relaxing dislocations.
Can frustrations arise in Ising systems with multi-spin interactions of different signs?
Authors: Nencka-Ficek H.
Published: February 2003

Consider a 3-dimensional Ising system with mulit-spin interactions. Frustration due to w-spin interactions (w=2,3,4...) can arise in systems with coupling constants of different signs (±1) distributed in an exactly determined manner. If each coupling constant is negative and w=3, frustration can arise in spherical or hyperbolical but not in euclidean lattices.
An infinite-range bond percolation
Authors: Wu F. Y.
Published: February 2003

A bond percolation on a lattice in which all pairs of vertices are connected is considered. The percolation problem is treated by carrying out the Kasteleyn-Fourtuin formulation of taking the q=1 limit of a related q-component Potts model; the latter is exactly solved. For a lattice of N sites, an average of pN occupied bonds and N large, it is found that the system is percolating for p≳1/2. Closed-form expression is also obtained for the moment-generating function of the cluster size. The analysis yields the mean-field exponents β=γ=γ′=1.
Monte Carlo simulation of the spin-glass transition of a dilute Ising model on a triangular lattice
Authors: Fernández J. F. , Andérico C. Z. , Streit T. S. J.
Published: February 2003

We study the critical properties of an Ising model with nearest neighbor antiferromagnetic interactions, placed on a triangular lattice, where each site is occupied by a spin, only with x probability. Randomness and frustration, two essential ingredients of spin-glasses, are present in this model. The entropy is obtained, by a transfer matrix calculation, as a function of x at low temperature (T=0.3 J/kB), for systems on a lattice of 10×19 sites. A fairly shallow minimum in the entropy appears near x=0.9, which suggests that this case is the most likely to show a transition into an ordered state at low temperature. We therefore simulate systems on lattices of 50×50 sites for x=0.9 and x=1 by the Monte Carlo method. The specific heat has a broad maximum at T=0.9 J/kB (1.2) for x=0.9 (1). The relaxation time (τ) obtained for T≥0.6 J/kB, turns out to be proportional to exp[A/(T−T0)c], and 0<T0≲0.4 J/kB; a fit with T0=0 yields c≂1 for x=1 but c≂2 for x=0.9.
Antiferromagnetic superconductors (invited)
Authors: Fulde P. , Zwicknagl G.
Published: February 2003

At present a number of antiferromagnetic superconductors are known to exist. The most significant effect of the onset of antiferromagnetic order in a superconductor is a characteristic change in the temperature dependence of the upper critical field Hc2(T). It indicates a weakening of the superconducting pairing due to the antiferromagnetic molecular field. We want to discuss the theory of these phenomena and show that it can explain the changes in Hc2(T) without requiring fit parameters. It is shown that the pairing prescription must be modified as proposed by Baltensperger and Strässler when an antiferromagnetic molecular field is set up. The resulting decrease in the attraction of electrons forming a pair is the main effect of antiferromagnetic order on superconductivity.
Magnetic structure of TbAgCu4
Authors: Kaneko T. , Kamigaki K. , Abe S. , Ohashi M.
Published: February 2003

The magnetic susceptibility of TbAgCu4 has been measured between 4.2 and 400 K. The results are TN=11.5±0.5 K, θp=9 K, and μeff=10.3 μB. Neutron diffraction experiments were performed on polycrystalline specimen at temperatures 4.2–20, 77, and 300 K. The magnetic spin structure was determined to be like that of FeO: the magnetic spins align ferromagnetically in sheets parallel to the (111) plane and couple antiferromagnetically with adjacent sheets. The magnetic spin axis is directed along [111]. The magnetic moment for Tb is obtained to be 9±0.4 μB.
Kondo lattice mixed valence behavior in the Ce(SnxPb1−x)3 system
Authors: Teter J. , Freitag R. , Maury* A. , Crow J. E. , Mihalisin T.
Published: February 2003

Measurements of the electrical resistivity versus x and temperature T, for 1.5≤T≤300 K for the fcc system Ce(SnxPb1−x)3 are reported. CeSn3 has been shown to be a strongly mixed valent system with an average occupation number of the Ce 4f level nf of ∼0.4 at low temperatures. The electrical resistivity for Ce(SnxPb1−x)3 is compared to that obtained for other Ce based mixed valent–trivalent systems and to the predictions of the Newns and Hewson theory. These comparisons suggest that Ce(SnxPb1−x)3 is mixed valent for x≳0.5 and the scaling of the resistivity supports the previous result that CeSn3 is strong mixed valent with nf≂0.4.
Experimental study of the magnetic critical behavior of the Ni(001) and Ni(110) surfaces (invited)
Authors: Alvarado S. F. , Campagna M. , Ciccacci F. , Hopster H.
Published: February 2003

Dedicated to Professor S. Methfessel, upon the occasion of his sixtieth birthday.   The critical behavior of the surface magnetization of atomically clean Ni surfaces has been studied by spin polarized low energy electron diffraction. The critical exponent β1 of the order parameter—surface magnetization—is determined from the temperature dependence of the magnetic exchange scattering asymmetry for the specularly reflected beam at various angles of incidence and kinetic energies of the primary beam. For the (001) surface we find β1=0.8 and for the (110) surface β1=0.79, with a statistical uncertainty of ±0.02. The difference in the critical exponent for the two surfaces is thus within experimental accuracy. This indicates that the larger surface relaxation of the (110) surface does not significantly influence the value of the critical exponent β1 in the temperature range 0.002≲1−T/TC≲0.1. The experimental values of the critical exponent β1 are slightly smaller than the predictions of ε-expansion calculations for the Heisenberg model (n=d=3), which lie in the range (0.81–0.88).
Observation of the high frequency spin wave branch and the uniform precession mode in FeBO3 by Brillouin scattering
Authors: Wettling W. , Wilber W. D. , Patton C. E.
Published: February 2003

Brillouin scattering has been used to observe the two spin wave branches of the weak ferromanget FeBO3. The high frequency, quasiantiferromagnetic branch is seen by this method for the first time. The temperature dependence of this branch is measured and compared with previous FMR measurements. An asymmetry is found between the Stokes and anti-Stokes scattering intensities for this mode which is dependent on the incident polarization. This is attributed to an interference between linear and quadratic magneto-optic effects. Scattering from the low frequency, quasiferromagnetic branch at very small wave vectors has also been measured. This was done using a forward scattering configuration.
Raman scattering from magnons and excitons in the 3-D ordered phases of CsCoBr3
Authors: Lockwood D. J. , Johnstone I. W.
Published: February 2003

Hexagonal CsCoBr3 contains chains of Co2+ ions and exhibits three magnetic phases comprising a fully ordered triangular Ising lattice (T≲10 K), a partially disordered lattice (14 K≲T<28 K), and a disordered lattice that still retains significant intrachain spin correlations along the c axis. We have investigated the temperature dependence of the magnon and lowest excitons using Raman spectroscopy. For T≳30 K the magnon scattering appears as an asymmetric peak near 100 cm−1 superimposed on a broader band. On cooling, the spectrum is remarkable for the appearance of a series of discrete lines. The integrated intensities of prominent bands at 97, 102, and 105 cm−1 provide a measure of the 3-D magnetic ordering. The Co2+ excitons observed at 324, and 360, and 385 cm−1 in the 1-D phase each split into narrow components at the onset of 3-D order. For example, the 324 cm−1 band branches into lines at 322, 324, 327, and 329 cm−1. The relative intensities of the 324, 327, and 329 cm−1 lines have a similar temperature dependence to those at 97, 102, and 105 cm−1, respectively. The splittings of this exciton are one half that of the magnon indicating it experiences a smaller effective interchain exchange.
Magneto-optic Kerr effect of amorphous Gd–Fe–Co films
Authors: Tsunashima S. , Masui S. , Kobayashi T. , Uchiyama S.
Published: February 2003

Amorphous Gdx(Fe1−yCoy)1−x (0.25<x<0.28, 0<y<0.39) films have been prepared by coevaporation technique. The films exhibit the magnetization perpendicular to the film plane, and the Curie temperature rises with increasing Co content. The magneto-optic polar Kerr rotation angel θk has been measured in the temperature range of 300–450 K. It is found that Co substituted films exhibit larger θk than Gd–Fe films in the wavelength range of 400–700 nm. The effect of Co substitution is very significant in high temperature range because of the high Curie temperature. The temperature dependence of θk can be fitted to magnetization of 3-d transition metal sublattice using the mean field model, while the increase of θk at ambient temperature cannot be attributed to the rise of the Curie temperature.
Magneto-optical effects of aluminum and ferrous substituted cobalt ferrite
Authors: Peeters W. L. , Martens J. W. D.
Published: February 2003

The polar Kerr rotation of polycrystalline CoFe2−xAlxO4 (0≤x≤0.8) and CoxFe3−xO4 (0≤x≤1.0) was measured in the energy region 0.6 eV≤E≤5.5 eV. The Faraday rotation of thin polycrystalline films of CoFe2−xAlx O4 (x=0.1 and 0.6) was measured in the energy region of 0.6 eV≤E≤2.8 eV. The spectra in the energy region below 3 eV are discussed in terms of crystal field transitions of Co2+ (Td). Furthermore a new intense transition is observed around 2 eV. This transition is assigned to a charge transfer of Co2+ to Fe3+, both on the octahedral site.
Magneto-optic and magnetic properties of praseodymium substituted garnets
Authors: Leycuras C. , Le Gall H. , Desvignes J. M. , Guillot M. , Marchand A.
Published: February 2003

On PrxY3−x Fe5O12 substituted garnets magnetic magnetization and Faraday rotation (φF) have been measured in the 4.2–300 K temperature range with magnetic field applied parallel to the ‖111‖ direction. The wavelength varies from 1 to 1.3 μm and three Pr3+ concentrations 1.10, 0.70, and 0.35 were studied. At 4.2 K, the spontaneous magnetic moment attributed to one Pr3 ion is deduced from the Néel model to be (1.55±0.15) μB as previously found in polycrystalline samples. At 1.15 μm wavelength the contribution of the Pr sublattice to φF is determined assuming the contribution of the Fe3+ ions equal to the YIG experiemental data. φF induced by one Pr3+ ion is found identical in the three ferrites of various concentrations for T≳90 K. Below this temperature, discrepencies of about 15% between the Pr3+ contributions to φF were evaluated. Characteristic values are obtained: −(475±25) deg cm−1 at 300 K, −(700±50) deg cm−1 at 90 K, −(1800±200) deg cm−1 at 9 K. Such a behavior which shows the one ion model to be valid is completed by the study of the θF dispersions in the 1.05–1.3 μm wavelength range at 300 and 77 K, respectively. By comparison between diamagnetic and paramagnetic type Faraday contribution the high rotation of the Pr3+ ions is attributed to a newly observed paramagnetic transition close to 5500 Å (18.180 cm−1).
Band-structure details from high-precision magnetic torque measurements on single crystals of ferromagnetic metals (invited)
Authors: Franse J. J. M. , Gersdorf R.
Published: February 2003

Magnetic torque measurements at 4.2 K on spherical samples of Ni and Gd reveal some fine details in the density of electron states near the Fermi level. In Ni metal an anomalous contribution to the magnetic torque could be ascribed to the shift of the X2↓ level through the Fermi level upon rotation of the magnetization with respect to the crystal axes. An anomalous torque in Gd is explained with the shift through the Fermi level of the small peak in the density of states curve. Relevant parameters of these band-structure details in both metals could be determined from a quantitative analysis of the magnetic torque data.
Solitons in ferromagnetic spin-1 chains?
Authors: Schneider T. , Stoll E.
Published: February 2003

We report finite-ring calculations revealing that spin-1 ferromagnetic easy-plane chains in a symmetry-breaking field are well described by a weakly interacting Bose gas. The thermally-induced central peak (CP) previously observed by neutron scattering from CsNiF3, and interpreted in terms of solitons, is traced back to annihilation/creation processes of the excitations. Its temperature variation shows a pronounced interaction-mediated saturation. The essential features of the spin dynamics and of the field and temperature dependence of the specific heat can be explained without solitons. We predict corresponding CP phenomena in a large variety of spin systems.
Spin-Peierls transition in a Cu2+ linear chain
Authors: de Jongh L. J. , de Groot H. J. M. , Reedijk J.
Published: February 2003

We present susceptibility vs temperature and high-field (40 T) magnetization data on Cu-HTS. The data are interpreted in terms of a spin-Peierls transition at about 12 K in this antiferromagnetic S=1/2 linear chain compound.
Electrical resistivity and thermopower of amorphous FexCo80−xB20 alloys
Authors: Kettler W. , Wernhardt R. , Rosenberg M.
Published: February 2003

A systematic study of the electrical resistivity ρ and thermopower S of amorphous FexCo80−xB20 alloys in the temperature range 4 K<T<300 K has been undertaken. The analysis of the resistivity data reveals that both s–d scattering and scattering by structural disorder contribute to ρ. From the structural contribution to ρ reasonable values of the Debye temperature θ (280–400 K) have been estimated. The physical significance of the variation of the spin-disorder resistivity with x has been discussed in terms of the spin-wave stiffness constant D and the s–d exchange integral Jsd. The calculation of 2kF values from the experimental data according to the outlined transport model explicitly shows its limitation. The thermopower S is not linear over any large range of temperature contrary to the prediction of a pure structural transport model. The thermal behavior and the variation of the room temperature values of S with x is similar to that observed in crystalline Fe–Ni alloys. It is argued that the extension of Kasuya’s relation based upon the s–d exchange interaction model should provide an approximate description of the temperature dependence S of ferromagnetic amorphous alloys.
Electrical resistivity of amorphous Ni80−xMxB16Si4 alloys
Authors: Park T. S. , Sostarich M.
Published: February 2003

The electrical resistivity of amorphous Ni80−xMxB16Si4 alloys, M standing for any of the 3d transition metals, was studied in the temperature range ∼2–950 K. The resistivity versus M plots (at constant x) yield typical double-peaked curves, with a minimum at Mn. The origin of this resistivity behaviour is discussed. All the samples show a resistivity minimum, probably due to Kondo effect, at Tmin, which is strongly composition dependent. Negative temperature coefficients of resistivity found about room temperature for several alloys are the consequence of Tmin lying well above room temperature for those alloys.
Concentration dependences of electrical resistivity and magnetoresistance of Fe-P amorphous alloys
Authors: Fukamichi K. , Gambino R. J. , McGuire T. R.
Published: February 2003

Fe-P amorphous ribbons were prepared by melt quenching, and the concentration and temperature dependences of electrical resistivity, magnetoresistance, and forced magnetoresistivity have been investigated. The room temperature electrical resistivity monotonically increases with P content. The Debye temperature determined from the temperature dependence of electrical resistivity of Fe-P amorphous alloys is lower than that of Fe-B amorphous alloys. The concentration and temperature dependences of the anisotropic magnetoresistance are not associated with the magnetization or the linear magnetostriction at low P contents. The magnitude of the negative forced magnetoresistivity becomes larger with increasing P content and temperature.
Magnetostriction in polycrystal Pr2(Co1−xFex)17 compounds and their easy directions of magnetization
Authors: Mori K. , Hathaway K. , Clark A. E.
Published: February 2003

The temperature and field dependences of the magnetostriction, λ∥−λ⊥ of Pr2(Co1−xFex)17 compounds for x=0 to 1 were measured from 80 to 340 K. The magnetostriction shows a maximum for x=0.8 of λs∼307×10−6 and ∼1060×10−6 at room temperature and 80 K, respectively. From these measurements the phase diagram of the spin reorientation temperature Tm versus iron content x was obtained.
Effect of heat treatment on piezomagnetic properties of Al–Co–Fe alloys
Authors: Kaczkowski Z.
Published: February 2003

The aluminium–cobalt–iron alloys (Alcofers), containing from 12 to 14 wt. % Al and to 3 wt. % Co were investigated. Piezomagnetic coefficients, appearing in piezomagnetic (magnetostrictive) equations, versus magnetic bias were obtained after annealing in H2 for 2 h at 750 to 1300 °C temperatures and cooling in furnace. Some results, especially for thermal treatment providing the best magnetomechanical coupling (k≳0.3), are presented. Small amounts of Co in Al–Fe alloys improve piezomagnetic properties of materials, connected with partially ordered structure DO3 type.
A novel approach of the magnetoelectric effects in ferrimagnets (invited)
Authors: Aubert G.
Published: February 2003

A general thermodynamic method is proposed for analyzing the magnetoelectric properties of paraelectric ferro- or ferrimagnets. Various experiments on lithium ferrite are discussed in this frame and a remarkable agreement is found with the proposed model. This model suggests new experimental arrangements more suitable for getting the characteristic parameters and gives a deeper physical insight on the possible microscopic mechanisms.
Irreversible magnetization processes induced by thermal cycling and by ultrasound in Bi–MnBi
Authors: Winter Calvin , Arrott A. S.
Published: February 2003

Directionally solidified near-eutectic MnBi forms a precipitate of long rods of Low Temperature Phase (LTP) and a high coercivity New Phase (NP) MnBi in a Bi matrix (2 microns and smaller in diameter). The Curie temperature of the NP is 247±5 K. Particles of both phases magnetize irreversibly by switching, but are not always single domain. The phases interact magnetically. The LTP phase has an intrinsic coercivity of 700 Oe at 120 K, and this can by reduced by 18 Oe by the application of ultrasound stresses of 107 dyn/cm2.
Temperature dependence of domain wall resonance in CrBr3
Authors: Jedryka E. , Yeh R. J. , Ramesh M. , Wigen P. E. , Pajaczkowska A.
Published: February 2003

Domain wall resonance has been observed in the purely uniaxial Heisenberg ferromagnet, CrBr3. In zero applied field the resonance frequency is observed to vary between 250 and 730 MHz and to decrease with the increasing sample thickness. The increase in the frequency with the applied in-plane field and the slight variation of the frequency with temperature are in good agreement with the Morkowski model.
Open boundary finite elements for axisymmetric magnetic and skin effect problems
Authors: Brauer John R.
Published: February 2003

Finite element techniques are described for calculating magnetic fields and eddy current distributions in problems with open boundaries. A new matrix recursion algorithm is derived for axisymmetric problems and is applied to the case of a circular coil in free space. Also discussed are open boundary skin effect problems, including an example of three double-channel bus bars. Solutions using the open boundary finite elements are shown to agree closely with classical solutions or with measurements.
Precise minicomputer finite element analysis of local magnetic fields by iteratively dividing region
Authors: Nakamae E. , Harada K. , Dohi Y. , Okano T. , Yamashita H. , Hammam M. S. A. A.
Published: February 2003

An iterative procedure giving remarkably precise magnetic flux density estimation by using a mini-computer is proposed. The outstanding features of the method are the introduction of the second order approximating function into triangular elements and of a newly proposed method of subdividing the region of the analysis; they diminish the number of required elements.
Torque of solid salient pole machine by finite element method
Authors: Yamada H. , Fujibayashi K.
Published: February 2003

This paper presents a method of deriving the average torque of solid salient pole machine by finite element method (FEM).1 In this calculation, the effect of the armature resistance is included. The harmonic torque associated with the Görge effect (the dip in the torque curve at half rated speed) need to be examined as that can affect the torque close to half speed. The direct axis impedance and the quadrature axis impedance of rotor side at asynchronous operation of solid salient pole machine are obtained by a Poynting vector calculation.2 But by the average torque calculation in the literature (2), armature resistance was neglected. The method presented in this paper has been applied to analyze a 4-pole, 3-kVA, 220-volt, 50-Hz solid pole machine. The computed result shows good agreement with the test data. As the impedance is obtained from the flux distribution by FEM, the torque obtained is more accurate than the conventional method.
Observation of an anomalous peak and hysteresis effect in silver diamagnetic susceptibility
Authors: Plumier R. , Sougi M. , Lecomte M.
Published: February 2003

Detailed measurements of high purity Ag susceptibility have been performed in the temperature range 4–300 K using a Faraday balance of 10−6 g sensitivity. Down to 55 K, the results are the same for a powdered sample and for an ingot made of the same powder. At T<55 K, different results are obtained. Whereas the susceptibility of the ingot keeps an almost fixed value down to 4 K, the powder susceptibility has a maximum at T=45 K and, in addition, at T<45 K a different behaviour according to the experiment is performed by slow or fast cooling down to 4 K.
Small angle neutron scattering in Ni3Al
Authors: Bernhoeft N. R. , Cole I. , Lonzarich G. G. , Squires G. L.
Published: February 2003

The temperature dependence of small angle neutron scattering in weakly ferromagnetic Ni3Al has been investigated by means of multi-detector small-angle spectrometers at A.E.R.E. Harwell and I.L.L. Grenoble. Measurements are reported in three stoichiometric samples with residual resistivity ratios [RRR=ρ(293 K)/ρ(4.2 K)] of up to 40 and in a Ni rich specimen (Ni75.4Al24.6). The cross sections in stoichiometric specimens exhibit an approximately linear rise with temperature well below the Curie point (TC=41±1 K), a peak around TC and a fall approximately proportional to (T−TC)−1 above TC. This behaviour is interpreted in a Ginzburg-Landau model of magnetic fluctuations involving a single adjustable parameter, from which a spin correlation length around TC and an effective spin-wave stiffness well below TC may be derived. Finally the possible qualitative features of the overall transverse magnetic fluctuation spectrum of Ni3Al are examined and a simple model is noted which can account for the observed fall in magnetization at low temperatures.
Semiconducting properties of a low resistive Ca-doped YIG film
Authors: D’Amico A. , De Gasperis P.
Published: February 2003

A low resistivity p-semiconductor Ca:YIG film containing Fe4+ ions has been investigated. In particular, the temperature dependence, the magnetogradient conductivity, and the bolometer responsivity of this material have been analyzed in detail. Main results can be summarized as: (i) a large increase of the conductivity causing a negative magnetoresistance of 26% for gradient field of 1500 G/cm; (ii) high responsivity values exhibited by this material when it is used in bolometer applications where resistance temperature coefficient of about −0.04/°C has been measured.
Effect of thermal and field cycling on the magnetoresistivity of CuMn spin glass
Authors: Senoussi S.
Published: February 2003

We report measurements of the magnetoresistivity of CuMn 4.7% and CuMn 1.35% after a number of different magnetic and thermal cycles in the spin glass state. First, our CuMn 4.7% sample was cooled in zero field down to 1.2 K and then submitted for a short time to some maximum field Hmax. Immediately after Hmax was removed the low field (LF) Δρ versus H curve was plotted. Similar low H measurements were then repeated for increasing strengths of Hmax. Two marked shoulders take place at Hmax≊15 kG and become very sharp for Hmax≳30 kG. In order to see whether or not the LF loop is reproducible we measured the same loop about 10 times and found a marked narrowing of the cycle of about 40%. This result cannot be described by a rigid anisotropy axis for which we rather expect a widening of the loop. Examples showing how the form of the LF magnetoresistance loop changes when the temperature is varied in H=0 are presented.
Electrical conduction in amorphous Gd–Co films
Authors: Okuno H. , Sakurai Y.
Published: February 2003

The composition and temperature dependence of electrical resistivity were studied for a series of amorphous Gd–Co films prepared by rf-sputtering method. The composition of films ranged from 23 to 42 at. % Gd and temperature from 4.2 to 300 K. Electrical resistivity, film composition, and thickness were measured by the four probe technique, electron microprobe, and TALYSTEP, respectively. The amorphous structure of sample was confirmed by x-ray diffraction with Co Kα radiation. With increasing Gd concentration the electrical resistivity at 4.2 K increased from 180 to 350 μΩ-cm and the temperature coefficient of resistivity at 288 K decreased and became negative above 220 μΩ-cm. The logarithmic and power-law temperature dependence of resistivity were observed at temperatures from 4.2 to 20 K and from 40 to 300 K, respectively. Both slopes of resistivity vs temperature curves increased with Gd concentration.