bluuebunny/crossref_metadata_2025 huggingface dataset:
Monte Carlo study of the arbitrary q-state Potts model
Authors: Novotny M.
Published: February 2003

A method of performing Monte Carlo simulations on the q-state Potts model is presented in which q may be treated as an arbitrary parameter. This allows the energy and specific heat of the q-state Potts model to be studied as a function of q and temperature. Results on the square lattice for several values of q are reported for both the ferromagnetic and antiferromagnetic Potts model.
Field-dependent specific heat study of the spin-Peierls transition in TTF–AuS4C4(CF3)4
Authors: Northby J. A. , Greidanus F. J. A. M. , Huiskamp W. J. , de Jongh L. J. , Jacobs I. S. , Interrante L. V.
Published: February 2003

The compound TTF–AuS4C4(CF3)4 is one of the very few existing examples of the spin-Peierls transition, in which a system of 1D antiferromagnetic chains dimerizes spontaneously as a consequence of magnetoelastic coupling with the surrounding lattice. We have studied the spectific heat anomaly accompanying the SP transition for this compound as a function of an applied magnetic field. Our H=0 data differ considerably from those obtained earlier by Wei et al., and in fact remove the discrepancy found by them between their results for TTF-AuS4C4(CF3)4 and the isomorphous TTF–CuS4C4(CF3)4. The differences between the two experiments are probably due to thermal relaxation effects. The combination of the specific heat data now available confirms the conclusion drawn from our previous field-dependent differential susceptibility studies on the Au compound, namely that the SP transition involves a considerable degree of short-range order, starting to develop below T=1.2 Tsp. We have been able to follow the specific heat anomaly for fields up to the multicritical point in the H–T phase diagram.
High-field (40 T) magnetization studies of linear Heisenberg chains with alternating exchange
Authors: de Groot H.J.M. , de Jongh L. J. , Willett R. D. , Reedijk J.
Published: February 2003

We present susceptibility vs temperature, and high-field magnetization data on two Cu2+ chain compounds with alternating exchange constants.
The magnetization of thin films with perpendicular anisotropy and columnar microstructures
Authors: Bernstein P.
Published: February 2003

The existence of a columnar microstructure is often invoked as the causes of perpendicular anisotropy of thin films. In this paper a model is presented for the process of magnetization of such films. The magnetic energy density is calculated for an isolated column taking into account the influence of the intercolumnar matter. The usual equilibrium conditions lead to an equation which is somewhat different from the classical astroid equation of a thin film. The experimental results and theory are compared for evaporated TbFe and sputtered FeTbGd samples.
Clarification of the different roles of surface anisotropy for thermal spin waves and FMR modes
Authors: Rado G. T. , Walker J. C.
Published: February 2003

Measurements by Mössbauer spectroscopy of the position dependence of the hyperfine field in monocrystalline iron films show that the fractional deviation of the spontaneous magnetization at temperature T from its value at T=0 K is larger by a factor of about two at a film surface than in the film’s interior. This result agrees with an early theoretical prediction of a factor of exactly two which is based on the assumption that the surface anisotropy is zero. In contrast, the results of recent ferromagnetic resonance experiments on ultra-thin films of monocrystalline iron were shown to be dominated by a surface anistropy which is nonzero. This discrepancy is reconciled for measurements at T=300 K by making use of the general boundary condition which contains the exchange stiffness A and some component(s) of the surface anisotropy Ksurf. The crucial argument is that at 300 K the thermally excited spin wavelengths are so short that at the film surfaces the normal derivative 2A∂m↘/∂n of the oscillating magnetization m↘ is very much larger than Ksurfm↘. Thus Ksurfm↘ is neglible for thermal spin waves even though it is comparable to 2A∂m↘/∂n for the long decay distances (or wavelengths) occurring in ferromagnetic resonance.
Ferromagnetic resonance studies of very thin epitaxial single crystals of iron
Authors: Krebs J. J. , Rachford F. J. , Lubitz P. , Prinz G. A.
Published: February 2003

Ferromagnetic resonance (FMR) has been used to study a wide variety of very thin single crystals of Fe grown on (110) GaAs substrates by molecular beam epitaxy. Data were taken at room and liquid nitrogen temperatures for films with thicknesses L in the range 18–200 Å. Due to surface anisotropy, the easy axis of the magnetization switches from [100] to [110] when L≤50 Å, independent of whether the the film surface is passivated by an Al-overcoat or has a thin Fe oxide surface layer. We suggest that this is an effective surface anisotropy arising in part from a depth dependent strain near the film-substrate interface. The changes in the parameters describing the angular dependence of the FMR spectra upon cooling to 77 K can be explained as due to magnetostriction arising from thermally induced strains plus the temperature dependence of the cubic volume anisotropy. The FMR linewidth is shown to be a linear function of frequency in the range 5–40 GHz.
Surface acoustic wave propagation in MnF2
Authors: Lingner C. , Lüthi B.
Published: February 2003

The temperature and magnetic field dependence of surface acoustic wave velocities in MnF2 single crystals has been investigated. Wave propagation was on a free (001)-plane in [100] and [110]-direction. The temperature dependence can be explained quantitatively by an elastic continuum approach. Experiments reveal the bulk spin flop at Bc∼9.3 T at 4.2 K. No evidence is found for a surface spin flop at lower field, Bsc∼6.6 T.
Valence state of europium in EuPd3Bx alloys: Lattice constant and susceptiblity studies
Authors: Dhar S. K. , Malik S. K. , Rambabu D. , Vijayaraghavan R.
Published: February 2003

New boron-containing alloys of the formula EuPd3Bx have been synthesized by alloying EuPd3 (having the AuCu3-type structure) with boron. The boron presumably occupies the vacant body-centered position in the EuPd3 unit cell and results in the expansion of the lattice. The increase in cell volume is observed to be much larger in EuPd3Bx alloys compared to that, for instance, in LaPd3Bx and GdPd3Bx alloys and suggests a possible change in the valency of europium from trivalent towards divalent on boron addition. Susceptibility measurements on EuPd3Bx alloys have verified the valence change of europium ions.
Magnetic correlations near the critical concentration in P
d Ni alloys
Authors: Burke S. K. , Cywinski R. , Lindley E. J. , Rainford B. D.
Published: February 2003

The temperature dependence of the neutron small angle scattering from dilute Pd Ni alloys has been investigated. The critical concentration for the onset of ferromagnetism was determined from the variation of TC and the intensity of the critical scattering with Ni concentration. Our result of 2.30±0.05% Ni confirms the estimate of Murani et al. [1]. The temperature and concentration dependence of the correlation range ξ was also studied. ξ was found not to diverge at TC, though it displayed a scaling behaviour similar to that found in Cr Fe alloys. This suggests that percolation may play an important role in the onset of ferromagnetism in Pd Ni alloys.
Magnetic moment distribution in Fe0.68 60Ni0.32
Authors: Cable J. W. , Brundage W. E.
Published: February 2003

The polarized-neutron, diffuse scattering method was used to investigate the magnetic moment distribution in Fe0.68 60Ni0.32. The measurements were made on an isotopic single crystal at 295 K in a magnetizing field of 2.0 T. These yield a difference in average moments of 0.46 μB which can be combined with the known magnetization of 0.95 μB to give average ferromagnetic moments of 1.10 μB/Fe and 0.64 μB/Ni. Pronounced local environment effects are observed, and these are negative except for the second neighbor effect. This sign sequence suggests the presence of some antiparallel alignment of Fe moments.
Theory and application of highly magnetoelastic Metglas 2605SC (invited)
Authors: Savage H. T. , Spano M. L.
Published: February 2003

We show by a variety of experiments that the magnetomechanical coupling k in Metglas 2605SC has larger values than in any other device material. Our Mössbauer experiments show that the anisotropy axis is quite well defined when compared with Metglas 2605CO. The small value of the anisotropy and the well defined axis lead to a value of 7 for the ‘‘ΔE effect,’’ a very large value. By assuming a small vestigial shear stress we derive from basic principles expressions that describe the macroscopic magnetoelastic characteristics of 2605SC. We are able to fit our dynamic coupling factor data with parameters from our static stress measurements. This is the first time such a description has been presented, and we use it to predict the performance of a magnetomechanical strain gage. We show that such a strain gage can have 103 to 105 more sensitivity than a conventional strain gage. We discuss the attempts of other authors to build devices and present prototype device designs. We show that the material has other advantages for devices such as a lack of Barkhausen noise and good low frequency characteristics.
Thermal, magnetic, and magnetomechanical properties of Metglas 2605 S2 and S3
Authors: Kabacoff L. T.
Published: February 2003

The magnetomechanical coupling factor K33 (as a function of annealing temperature Ta and bias field) and crystallization characteristics have been measured for two metallic glasses, Metglas 2605 S2 and S3. In the S3 alloy, K33 increases with increasing Ta, with a maximum of 0.85 between 385 and 400 °C, and declines sharply above 400 °C. S2, on the other hand, has a broad plateau in K33 between 400 and 430 °C (the upper limit of Ta in the experiment), with a value of K33 of 0.93. DSC curves show that both glasses crystallize in two stages with activation energies of 4.81 and 4.35 eV for S2 and S3. The Curie temperature TC was measured as a function of annealing time and temperature for the S2 composition. Plots of TC versus Ta show a straight line region, corresponding to structural relaxation, followed by a region of increasing slope, due to incipient crystallization. Samples of K33 which were magnetically annealed to produce high K33 and subsequently nonmagnetically annealed at 250 or 300 °C showed a decrease of K33. Following an additional magnetic anneal at 415 °C, the value of K33 was restored to its original value. It is clear from these results that loss of transducer function is due, not to crystallization effects, but to loss of anisotropy.
Magnetomechanical coupling, ΔE effect, and permeability in FeSiB and FeNiMoB alloys
Authors: Anderson III P. M.
Published: February 2003

Measurements of magnetomechanical coupling, ΔE effect, and relative permeability have been made as a function of bias field and annealing temperature and time in transversely annealed samples of Metglas R a) alloy 2605S-2 (Fe78Si9B13), Metglas alloy 2605S-3 (Fe79Si5B16), and Metglas alloy 2826MB (Fe40Ni38Mo4B18). Annealing temperatures and times were varied from 300 to 450 °C and 15 to 60 min, respectively. The bias field which generates the largest coupling factor in these alloys is less than 1 Oe. From an application point of view, this low optimum field has a distinct advantage in power requirements over the 11 Oe field required for Metglas alloy 2605CO1 but the low field requirement is a marked disadvantage when considering bias field stability. That is, a 0.5 Oe change in field can result in greatly reduced coupling in the present alloys versus a very small change in 2605CO.
Effect of superimposed stress waves on magnetization changes in S
bMn alloys
Authors: Önengüt D. , Schröder K.
Published: February 2003

SbMn alloys with 8.0 to 17.5 a/o Mn, essentially Sb with SbMn precipitates, showed uniaxial crystal anisotropy in magnetization measurements between 127 and 296 K. Stress pulses produced irreversible magnetization changes. They were nearly independent of temperature. This is associated with the shape anisotropy of the SbMn precipitate. Some samples were subjected to two stress waves from transducers attached on opposite sides of the sample. The simultaneous operation of transducers generated a larger magnetization change than each transducer operated individually.
Magnetic birefringence (invited)
Authors: Gehring G. A.
Published: February 2003

A review is given of some aspects of magnetic birefringence. We describe the attemps that have been made to understand its microscopic origins and its use in measuring magnetic phase diagrams and critical exponents. The fluctuations of the birefringence away from its average contribute to the background intensity. Magnetoelectric crystals can show a gyrotropic birefringence.
Two magnon Raman scattering in Cd1−xMnxTe
Authors: Picquart M. , Gryndberg M.
Published: February 2003

Manganese cadmium tellurides are ternary compounds belonging to the family of so-called semimagnetic semiconductors. We present results of Raman scattering by two magnon for concentrations 0.4<x<0.68 in the temperature range 2 K<T< 90 K. At 2 K we observe a structure in the Raman spectra at low energy. This band shifts toward the low energy side when the temperature increases and disappears completely inside the Rayleigh line. The Ising cluster model permits us to obtain the spectral shape of the Raman scattered light.
Magneto-optic Kerr effect in CoFe2−xMxO4 (M=Mn, Cr, Al) and BaFe12−2x–COxTixO19 with tetrahedrally coordinated Co2+
Authors: Abe M. , Gomi M.
Published: February 2003

Polar Kerr effect has been observed at λ=0.4–2.0 μm on hot-pressed ceramics of Co2+Fe3+2−xM3+xO4 (M=Mn, Cr, Al, 0≤x≤1.2) and BaFe3+12−2x–Co2+xTi4+xO19 (0≤x≤1.5), in which tetrahedrally coordinated Co2+ ions [Co2+(Td)] increase with x. To avoid effect of birefringence in the hexagonal ferrite, ceramics with prefered orientation along the c axis have been prepared by a topotaxial reaction technique. Enhancement in the Kerr effect associated with the crystal field transitions of Co2+ (Td) is observed at λ≊0.7 and 1.7 μm in both CoFe2−xMxO4 and BaFe12−2x–CoxTixO19, though the magnitude in the latter compound is several times smaller than in the former. The large normal remanence observed by surface Kerr effect in CoFe2−xMxO4 can not be attributed to the residual stress induced by hot-pressing as has been pointed out previously.
Experimental study of the linear magnetic birefringence in erbium iron garnet
Authors: Feldmann P. , Gouzerh J. , Le Gall H. , Guillot M.
Published: February 2003

Linear magnetic birefringence (Cotton-Mouton effect) and optical axis position have been measured in Er3Fe5O12 crystals in the Voigt geometry in the 10–300 K temperature range. Deviation of the optical axis away from the magnetic field direction is found below the compensation temperature, when the magnetic field is not applied along the easy axis of magnetization [100]. Cotton-Mouton effect evolution is reported and compared with that of YIG and with magnetization of ErIG. A large anisotropy of ErIG Cotton-Mouton effect is observed, with sign of the slopes of Cotton-Mouton effect versus field depending on the field orientation.
Internal magnetic fields in hcp-iron
Authors: Taylor R. D. , Cort G. , Willis J. O.
Published: February 2003

The magnetic behavior of hcp-Fe (epsilon iron) has been investigated by the Mössbauer Effect over a wide range of temperature T, pressure P, and applied magnetic field H0. The internal field Hi of the induced moment is given by Hi=0.20±0.01 H0 and is independent of T and P. Enhanced paramagnetism is suggested as the most likely origin for a contribution of this magnitude to Hi.
Effect of thermal fluctuations on the kinetics of domain growth
Authors: Sahni P. S. , Grest G. S.
Published: February 2003

We have carried out Monte Carlo simulations using Kawasaki dynamics to study the effect of temperature on the growth kinetics of a circular domain of one degenerate ground state surrounded by a sea of the other degenerate ground state. As predicted by Lifshitz and Cahn-Allen theories, we find that the circular domain shrinks linearly with time as A(t)=A0−αt where A0 and A(t) are the initial and instantaneous areas, respectively. We also find a strong temperature dependence of the slope α for T≳0.6 TC which is tentatively interpreted as being due to roughening fluctuations.
Differential susceptibility as a magnetic probe: Some recent applications (invited)
Authors: van Duyneveldt A. J.
Published: February 2003

In this paper the experimental status of ac susceptibility measurements will be briefly mentioned, followed by two examples illustrating the various aspects in low, temperature magnetism which can be treated by ac susceptibility studies. The linear chain compound Co[(CH3)3NH]Cl3 ⋅ 2H2O exhibits a canted antiferromagnetic ordering below 4.179 K. It is discussed how this is seen in the zero-field susceptibilities, how the metamagnetic phase diagram is found, and how relaxational effects due to domain wall movements show up in the data. In metallic spin glasses the ac technique is used to determine the frequency dependent part of χ, and it is shown how this part reflects the type of interaction operative in the spin-glass freezing.
Spin-Peierls instability in the quasi d=1 magnetostrictive xy model (invited)
Authors: Tsallis C.
Published: February 2003

We discuss, within a framework where the magnetic (structural) degrees of freedom are exactly (adiabatically) taken into account, the spin-Peierls instability occuring in the magnetically one-dimensional and structurally three-dimensional magnetostrictive spin-1/2 xy model. Emphasis is given to the influence of an external magnetic field (along the Z axis) on the thermodynamical (phase diagram, structural order parameter, specific heat, magnetization, susceptibility) and dynamical (acoustic and optic phonons spectrum) quantities. We recover and extend several already known results; furthermore a certain number of facts is established and possible new effects are exhibited. In the T-H phase diagram, a structural Lifshitz point (LP) exists where the uniform (U), pure dimerized (D) and modulated (M) phases converge (the relative arrivals, on the LP, of the three critical and two metastability lines are determined); another special point is detected on the U-M line at large magnetic fields; the slope of the D-M first-order frontier is discussed; for high elastic constants, fixed temperatures and increasing magnetic field, the unusual sequence nonuniform–uniform–nonuniform–uniform is possible. The thermal dependence of the sound velocity presents a gap. The present theory is hopefully applicable (at least qualitatively) to substances like TTF-BDT, MEM(TCNQ)2 and eventually alkali-TCNQ.
Solitons in magnetic chains (invited)
Authors: de Jongh L. J.
Published: February 2003

Solitons in magnetic chains are moving domain walls, separating spin-up and spin-down regions in a ferromagnet, or the two different (degenerate) ordered configurations in an antiferromagnet. We discuss a few experiments which probe the existence of these nonlinear excitations in quasi 1-d magnetic materials, including neutron scattering, NMR, Mössbauer effect, and ac susceptibility. We further consider the application of the soliton model to the antiferromagnetic (H-T) phase diagram and to the problem of spin-Peierls dimerization.
Lattice instability and spin-Peierls phase transition in the alkali-TCNQ salts
Authors: Lépine Y.
Published: February 2003

The spin-Peierls phase transition is stuided in quasi-one-dimensional crystals of the alkali-TCNQ type. The displacement of the TCNQ molecules is described as a combination of a dimerization and a lateral shift. In the model presented here, the phase transition will be described as a combination of a longitudinal and a transverse mode becoming soft simultaneously. A lattice intrinsically unstable against dimerization is then combined with spin-Peierls mechanism to describe the phase transition. The anharmonic lattice dynamics are treated through a quasi-harmonic mean field approximation and the spin system is described by the usual pseudo-fermion formalism. It is found that for small coupling between the modes, because of the spin-phonon coupling terms, both modes soften simultaneously. For large negative coupling energies between the two modes, the phase transition becomes of first order. These results explain qualitatively the behavior of the alkali-TCNQ salts.
Low field Hall effect magnetometry
Authors: Daniil P. , Cohen E.
Published: February 2003

Low field Hall effect magnetometry has been limited by the performance of the offset (misalignment) voltage rejection technique used. In this work a method is employed where the offset voltage is eliminated without the need to know its exact value nor to make any calibration. To obtain long term stability a new idea is introduced whereby information present in the self field voltage is used to monitor the instrument calibration. These two techniques do not impose any particular requirements on Hall device performance. It is shown that the limiting parameters to the instrument sensitivity are the input bias current and the common mode rejection capability of the voltage sensing differential amplifier. The smallest Hall voltage that was detected was 500 nV, the equivalent of 4 μT field with the device used and no magnetic concentrator arrangement.
Factors affecting the performance of a thin film magnetoresistive vector magnetometer
Authors: Hoffman G. R. , Birtwistle J. K.
Published: February 2003

Thin nickel-iron films with uniaxial anisotropy are vacuum-deposited onto glass. A bridge-connected group of conductive meander patterns is formed by photo-lithography; the current flow in each pattern is aligned at 45° to the anisotropy axis and the magnetoresistors are subjected to bias fields perpendicular to this axis. External fields cause magnetic vector rotation, producing magnetoresistive changes which unbalance the bridge. Poles along the edges of each meander pattern strip generate a demagnetisation field. Its magnitude and direction can be calculated from the effective pole density, which changes with the film’s direction of magnetisation. The field is dependent on the geometry of the conducting strips. Calculation of the equilibrium magnetisation direction is based on the Stoner-Wohlfarth model, modified by the effects of the demagnetisation field. There is close correlation between theoretical and experimental results, particularly at higher bias levels where most of the film exists as a single domain. Vector magnetometers must have low sensitivity to orthogonal fields. Careful choice of pattern geometry and optimised bias fields in theory allow a zero orthogonal response, a prediction confirmed by experiment. The magnetometer has a linear response and the system noise is less than 1γ per Hz1/2.
Calorimeter for measuring ac magnetic losses in small samplesa)
Authors: Canright G. S. , Anderson R. L.
Published: February 2003

A calorimeter has been developed to measure the total core loss in small samples of magnetic materials which are not suited to conventional measurement techniques. The method is similar to the helium boil-off calorimeter used in some cases to measure ac losses in superconductors. Power losses in the sample are determined by measuring the rate of boiling of a fluid in which the sample is immersed. The sample is in open magnetic circuit. Uncertainty of the method is estimated at 3%.
An electronic coercivitimeter for amorphous ribbon toroids
Authors: Couroumalos C. , Price M. H. , Overshott K. J.
Published: February 2003

The constant current flux reset (C.C.F.R.) method has been frequently used to measure the coercivity Hc, remanence Brem, and saturation flux density Bmax, of nickel-iron alloys. A new electronic coercivitimeter has been constructed based upon the C.C.F.R. method, which is capable of measuring the properties of amorphous ribbon toroids. The mode of operation and circuit of the coercivitimeter will be fully described. The coercivity and remanence to maximum induction ratio, Brem/Bmax, of amorphous ribbons of Co58Ni10Fe5Si11B16 and Fe81B13.5Si3.5C2 which have been forward wound, i.e., with the wheel side of the ribbon on the side of the toroid and reverse wound, i.e., with the wheel side of the ribbon on the outside of the toroid, have been measured. The measurements presented have been made over the frequency range 50 to 1000 Hz and for toroids field annealed under different conditions, i.e., temperature from 325 to 425 °C, in air, nitrogen, and hydrogen atmospheres. It is found that the coercivity increases and the Brem/Bmax ratio decreases as the frequency increases. These experimental results are explained by considering the effect of annealing conditions and frequency on the domain structure, B/H loop, metallurgical properties, manufacturing stresses, and induced anisotropies of amorphous ribbons.
Physical origin of losses in conducting ferromagnetic materials (invited)
Authors: Graham C. D.
Published: February 2003

The physical origin of losses in conducting ferromagnetic materials is the production of heat by the flow of eddy currents in the material. The eddy currents are generated by the voltages caused by changes in the magnetic induction. This statement, although true, is not very helpful in calculating or predicting the actual magnitude of the losses. For such a calculation, we need a detailed knowledge of the mechanism of magnetization reversal. The present standing of efforts to predict losses is briefly reviewed and discussed.
Computation of losses in nonoriented electrical steels from a classical viewpoint (invited)
Authors: Del Vecchio R. M.
Published: February 2003

Nonoriented electrical steels approximate a classical continuum with respect to magnetic and electrical properties. A calculation based on fields which vary smoothly from point to point should therefore be appropriate. At each point, the paths taken by the magnetic fields in the B–H plane are influenced by eddy currents and the eddy currents in turn depend on the B–H paths. This mutual interaction prevents hysteresis and eddy current losses from being independent. The full electromagnetic problem, including these interactions, can be solved for simple geometries. At present we are restricted to solving unidirectional flux problems where convenient hysteresis models may be applied. These yield a reasonable description of complex hysteresis paths with only a limited amount of experimental input. Using a hysteresis model and numerical techniques, loss calculations for both sinusoidal and distorted flux waveforms in thin laminations were performed and are compared with experimental data.
Magnetoelastic coupling in dilute magnetic alloys
Authors: Creuzet G. , Campbell I. A.
Published: February 2003

We present magnetostriction measurements on dilute magnetic alloys. Systematic investigation has been performed on monocrystals through the silver–rare earth and gold–rare earth series. The results present very different behavior from one RE to another, but we obtain a very good agreement with a single ion model; we deduce the magnetoelastic coupling parameters which appear to be quite constant along the series and clearly in contradiction with the prediction of a point charge model. Measurements on a (LaAg)Tb single crystal give similar results and we are able to explain some surprising observations obtained on polycrystalline (YPd3)RE alloys.
Analysis of magnetoelastic wave propagation in a magnetic slab
Authors: Fujii T. , Inoue M. , Miyama T.
Published: February 2003

Properties of magnetoelastic wave in a magnetic slab possessing a uniaxial in-plane anisotropy is analyzed by solving dynamic equation of motion as a function of the thickness of the slab d. For k1d/2≪1, where K1 is the wave number, magnetoelastic wave is bulk wave, whereas it tends to surface wave as k1d/w increases. Its dispersion relation is subjected to change with external applied field. The dispersion relation at magnetic saturation coincides with that of Lamb wave in an elastic slab. For B (magnetoelastic coupling constant)=5×107 erg/cc and K (uniaxial anisotropy constant)=3×103 erg/cc, controllable change of the sound velocity ΔC/Cs (Cs: sound velocity at magnetic saturation) is about 14% for the bulk mode while it becomes about 30% for the surface mode.
Phonon excitation and propagation in thick iron films
Authors: Dewar G. , Alexandrakis G. C.
Published: February 2003

The generation and propagation of 9.37 GHz sound in polycrystalline iron films ∼13 μm thick is discussed. The excitation is accomplished via the magnetoelastic coupling and is optimized at FMR. No sound absorption dip or exchange asymmetry has been observed in these experiments.
The temperature dependence of magnetic anisotropy energy and magnetostriction of spins with n degrees of freedom
Authors: Callen E.
Published: February 2003

For spins of fixed length rotating in three space (two degrees of freedom, n=2) the anisotropy and magnetostriction coefficients of degree l vary at low temperatures as the l(l+1)/2 power of the magnetization. We demonstrate that for arbitrary number of degrees of freedom n the power of the magnetization is l(l+n−1)/n. We further demonstrate that at high temperatures, where the magnetization is small, the power of the magnetization is l, for all numbers of degrees of freedom.
A static ballooning technique for 2-D open boundary problems
Authors: Antunes C. F. R. L. , Freeman E. M. , Lowther D. , Silvester P.
Published: February 2003

The paper describes a differential technique for matching an interior problem region to an exterior, Laplacian region. The technique is based on the construction of a set of annuli around the interior region to model the exterior space. The annuli are specified by a mapping operation which is described in terms of the interior boundary nodes and the directions of expansion. A functional F in terms of the different directions of expansion is first defined and then differentiated to specify the mapping. Admittance matrices due to the exterior region are then easily obtained and combined to give a final admittance matrix which represents the effect of the exterior region on the interior boundary nodes.
Numerical mode pushing in domain level modelinga)
Authors: Torfeh-Isfahani M. , Della Torre E.
Published: February 2003

Due to the nonlinearity of modeling problems, iterative algorithms such as SOR have been used extensively. For some problems these algorithms exhibit stiff convergence (SC), which not only require an excessive number of iterations for solution but also admit large errors if they are terminated prematurely. The mode pushing (MP) algorithm is very effective in the solution of scalar elliptic partial-differential-integral equations with SC modes. This paper discusses the MP method and the problems that one runs into when computing the coercivity of ferromagnetic material.
Magnetic field computations by infinite elements
Authors: Kim In-ho , Jung Hyun-kyo , Lee Gi-shik , Hahn Song-yop
Published: February 2003

This paper describes the applications of the infinite element method to two-dimensional magnetic field problems. The system stiffness matrix is derived using the variational method, while boundary conditions at the interfaces of finite element regions and infinite element regions are dealt with using collocation method and modified variational method. The method is applied to two simple linear problems, and the results are compared with the analytic solutions. It is observed that the numerical solutions are in good agreement with the analytic solutions. It is also observed that the proposed method gives more accurate results than the standard finite element method.
Conduction electron contributions to the Sn hyperfine field in the Heusler alloy Co2Ti1−xVxSn
Authors: Dunlap R. A. , Stroink G.
Published: February 2003

Vibrating sample magnetization and 119Sn Mössbauer effect measurements were made on the series of Heusler alloys Co2Ti1−xVxSn (x=0.0, 0.2, 0.4, 0.6, 0.8, 1.0) to determine the moment carried by the Co atoms μ and the Sn hyperfine field H. These measurements yielded values of the field of +80 and +7 kOe and moments of 0.88 and 0.31 μB for the alloys Co2TiSn and Co2VSn, respectively. The Sn field showed a monotonic decrease as a function of x. The moment remained relatively constant for x≤0.8 and decreased dramatically for x=1.0. The results obtained here are discussed in terms of recent theoretical predications.
Magnetic behavior in the Fe3Al1 system
Authors: Orehotsky J. , Machado da Silva J. M. , Oliveira J. B.
Published: February 2003

The magnetic properties of the Fe3Al1 order-disorder system have been investigated. Magnetization results of a rapildy cooled sample and susceptibility measurements show that the Curie temperature of the partially ordered B2 phase is 590 °C. Slow cooling experiments indicate the the Curie temperature of the fully ordered DO3 phase is about 520 °C. These temperatures are not consistent with either previously determined values or with the predictions of a phenomenological model. The magnetization value at 25 °C in high fields of the DO3 phase is significantly larger than previously observed values and is also larger than the magnetization of the B2 phase as expected from past investigations. The possible existence of a previously undetected antiferromagnetic phase seems to be indicated by the magnetization data at low temperatures and fields of the DO3 sample. The prominent anomaly in the temperature dependence of the magnetization at the B2-DO3 order-disorder temperature has been investigated and the results are explained by the magnetic properties proposed for the B2 and the DO3 phases.
Co–Sn thin films: Magnetic and transport properties
Authors: McGuire T. R. , Aboaf J. , Klokholm E.
Published: February 2003

CoxSn1−x forms amorphous alloys when the atomic fraction of Co, x, is less than ≊0.8. The magnetization 4πM decreases with decreasing cobalt corresponding to the transfer of 1.9 electrons from the Sn to the Co band. For the composition at Co52Sn48 where 4πM goes to zero, the alloy has itinerant features. The spontaneous Hall effect increases with Co dilution and is highest for the compositions at x≊0.5 to 0.6. In contrast, the anisotropic magnetoresistance Δρ decreases with cobalt dilution but shows a weak maximum in Δρ, at x ≊0.8. There is a correlation of the magnetostriction with Δρ as a function of composition.
Magnetization and electrical resistivity studies of the HoNi single crystal
Authors: Sato K. , Isikawa Y. , Mori K.
Published: February 2003

The temperature dependences of the magnetization and the electrical resistivity of a HoNi single crystal were measured over the temperature range 4.2–300 K. It was shown that the easy direction of magnetization was inclined about 29° from the a*) axis and drew nearer to the a*) axis with increasing temperature. Above 15 K, the a*) axis became the easy direction of magnetization. Above the Curie temperature the curve of the electrical resistivity vs temperature has a negative curvature and is discussed on the basis of a band model by Mott and Jones.
Resistivity of amorphous Co–Mn–B alloys: Beyond the s–d model
Authors: O’Handley R. C. , Eberhart M. E. , Johnson K. H. , Grant N. J.
Published: February 2003

Absolute electrical resistivity of amorphous Co80−xMnxB20 ribbons has been measured. The objective was to study the effects on electron transport of the appearance near the Fermi level EF of Mn d states. The most striking result is that the resistivity does not increase smoothly upon increasing x. The data are interpreted in terms of cluster calculations which confirm the appearance at EF of early transition metal d states which are strongly admixed with the boron p states. Electrical conduction in the presence of these p–d hybrids differs markedly from that due to s- or d-like states in a transition metal alloy without metalloids.
Electron transport in Tb- and Pr-based metallic glasses
Authors: Cornelison S. G. , Sellmyer D. J.
Published: February 2003

Electrical resistivity measurements are reported on several metallic glasses based on Pr and Tb, and Ga and various transition metals as the glass formers. In general negative temperature coefficients were observed and these are discussed in terms of the extended Ziman theory and the tunneling or localization theory. Low temperature structure in the resistivity can be understood with the coherent exchange scattering model of Asomoza et al.
Electrical conduction in some glassy metal alloys in the presence of magnetic fields and tensile stresses
Authors: Aidun R. , Arajs Sigurds , Dokyi E. K. , Martin M. C.
Published: February 2003

The relative change in the electrical resistivity of glassy Fe80B20, Fe78Mo2B20, Fe40Ni40P14B6, and Fe32Ni36Cr14P12B6 have been investigated at 295 K as a function of longitudinal and transverse magnetic fields and tensile stresses. The low field magnetoresistivity of Fe32Ni36Cr14P12B6, which is nonferromagnetic at 295 K, is negligible. In principle, our data in the above ferromagnetic glasses are consistent with the expectations from the domain theory for positive magnetostrictive materials. However, the above glasses do not obey the equivalence principle between the magnetic field and the stress. It has been found that the ferromagnetic anisotropy of the electrical resistivity is approximately stress-independent.
A comparison of theoretical and experimental values of power loss of grain-oriented 3% silicon–iron
Authors: Morgan J. V. S. , Overshott K. J.
Published: February 2003

The localised power loss and domain wall movement under sinusoidal flux conditions has been measured for individual grains in polycrystalline Goss textured 3% silicon–iron. The power losses obtained from six models of wall motion were compared with the experimental losses. The rigid domain wall models (Pry and Bean, bra-ket array and skew walls) predicted losses higher than the measured values. The flexible domain wall models (Lee, isotropic bowing, and anisotropic bowing) predict losses closer to those measured. The best fit was obtained with a model which takes into account the variation of wall energy with wall orientation and includes the ruckling process, which confirms the published observations that ruckling is the major method of flux reversal. For peak sinusoidal flux densities Bm up to 1.6 T the power loss is proportional to (Bm)1.82. For stable and repetitive wall motion the power loss depends upon the average normalised wall velocity v as (v)1.88. The changes in domain wall spacing with frequency are also reported.
Frequency dependent hysteresis loss in SiFe
Authors: Seagle D. J. , Charap S. H.
Published: February 2003

We have studied the hysteresis loss associated with nonmagnetic inclusions that are large enough to support a supplementary domain structure. This tube domain structure interacts with a main domain wall by adhering to it as long as it is near enough to the inclusion. Loss is determined by the difference in stored tube energy between the first contact with the wall and the ultimate loss of contact. Experimentally, the area of contact decreases with increasing elongation of the supplementary structure; in our theory loss of contact occurs when this area goes to zero. The tube length at which the area of contact vanishes is significantly dependent upon the applied field, which itself must increase with increasing frequency as a result of the eddy currents loss associated with motion of the main domain walls. This implies that the tube will break free at differing lengths for differing frequencies. Our calculations show, for example, for one set of observed specimen parameters and a peak magnetization one-half of saturation, that the loss due to this mechanism increases by approximately a factor of 2 between zero frequency and 60 Hz.
The relation between carbon content and hot rolling temperature in developing high induction in boron silicon–iron
Authors: Fiedler H. C.
Published: February 2003

The development of high induction in boron silicon-iron involves satisfying both composition and processing requirements. One requirement for high induction, which necessitates complete secondary recrystallization to a strong (110) [001] texture, is sufficient carbon to assure the presence of some austenite at the hot rolling temperature. A related requirement is that a minimum of 3–4 ppm boron must be dissolved at the rolling temperature for the subsequent development of high induction. The objective of the work to be reported was to determine whether it would be beneficial to magnetic properties to raise the hot rolling temperature, thereby dissolving more boron, providing the carbon content was also raised to maintain the austenite content. Two sets of laboratory alloys, one with 30 ppm nitrogen and the other with 50 ppm nitrogen, and with carbon contents ranging 0.025% to 0.050%, were hot rolled from 1200, 1250, and 1300 °C. The highest inductions were obtained by hot rolling the 0.050% carbon alloys, whether with 30 or 50 ppm nitrogen, from 1250 or 1300 °C, with the higher rolling temperature giving the higher induction. It was concluded that increasing the hot rolling temperature, thereby dissolving more boron, is beneficial provided the carbon level is increased to maintain the austenite content around 5 volume percent. The major limitation of high austenite contents is severe edge cracking, as was encountered with about 20 volume percent.
Field and stress dependence of the magnetization in a ferromagnetic polycrystalline material of cubic structure
Authors: Bengtsson C. , Hörnfeldt S.
Published: February 2003

The effect of uniform tension on the magnetization of a ferromagnetic polycrystalline material of cubic structure is calculated by minimizing the free energy. The effect of magnetic stray fields in the grain boundaries is taken into account by considering units of three interacting grains. The final magnetization is obtained by averaging over such units neglecting the interaction between them. The model has been applied to a 2.7% Si–Fe alloy and shows good agreement with experimental data.
Transformation of indigenous iron-bearing phases during coal gasification
Authors: Jacobs I. S. , Federighi C. , McKee D. W. , Patchen H. J.
Published: February 2003

The reactivity of coal toward CO2 and steam is enhanced by indigenous mineral impurities or by added catalysts. The prominence of iron compounds among the natural impurities in coal and the known catalytic effect of metallic iron for carbon gasification suggests that such ‘‘iron-specific’’ techniques as Mössbauer spectroscopy and magnetization may provide unique insight into these effects. The early stages of coal gasification have been examined using the cited reactant gases on an Illinois no. 6 coal char at 900–950 °C, with no added catalysts. The iron-bearing minerals in the coal transformed in different ways depending on the gaseous environment. The dominant impurity pyrite FeS2 in the raw coal converted during the preliminary inert-gas pyrolysis at 700 °C to a pyrrhotite Fe1−xS. During CO2 gasification a major portion of the pyrrhotite was converted into magnetite Fe3O4. By contrast, during steam gasification, the iron remained in less oxidized states with important fractions found as wüstite, Fe1−xO, ferrous glass/silicates, and metallic iron. These differences may influence the catalytic activity of the iron in the two gaseous environments.
Metastable Fe nitrides with high Bs prepared by reactive sputtering
Authors: Kano* A. , Kazama N. S. , Fujimori H. , Takahashi T.
Published: February 2003

Preparation of thick films or bulk formed materials of Fe16N2 compound has been attempted using a high rate reactive-sputtering technique. As for the reactive gas, N2 was introduced with various pressures (PN2) into the chamber by mixing with Ar gas of about 10−2 Torr. About 0.5-mm thick bulk deposits were obtained through the continuous running with a 1000 Å/min rate. It has been found that the magnetization (σs) of about 240 emu/g exceeding the value for Fe can be obtained around PN2=0.1∼1×10−3 Torr. From thermomagnetization and x-ray analyses the increased σs is attributed to Fe16N2 compound, but the coexistence of bcc Fe and Fe4N prevents reaching the σs to the expected maximum value 298 emu/g of Fe16N2. From the application point of view, the presently obtained Fe nitrides are interesting in their coercivities and are useful for semihard magnets with high Vicker’s hardness (about 700 Hv).
Dilution induced instability in ferrofluids
Authors: Chantrell R. W. , Sidhu J. , Bissell P. R. , Bates P. A.
Published: February 2003

The effect of dilution on the stability of a ferrofluid consisting of cobalt particles in toluene has been measured. The ferrofluid was found to have a median particle diameter determined from magnetic measurements, of 5 nm. Prior to dilution the fluid was found to have long term gravitational stability, and the application of a uniform magnetic field induced only a small amount of aggregation. On dilution the fluid was found to become unstable due to the formation of large aggregates of particles. Measured settling velocities indicate that the agglomerates consisted of up to 106 particles and had radii of the order of 1μ. The effect is interpreted in terms of the equilibrium between adsorbed surfactant on the surface of the particles and free surfactant in solution in the base fluid. The implications of this effect as regards magnetic and physical measurements of the properties of ferrofluids as a function of concentration are discussed.
Electron spin resonance of Mn3O4 defects in MnOa)
Authors: Seehra M. S. , Srinivasan G.
Published: February 2003

Here we report the first observation of an electron spin resonance (ESR) line due to the Mn3O4 impurity in MnO. Using this ESR line (g≂2.005, linewidth ΔH≂100 Oe) as a probe, we have shown that Mn3O4 is primarily concentrated on the surface of MnO. The temperature dependence of the ESR line was investigated from 20 to 150 K. Anomalous changes in Hr (resonance field) and ΔH are observed near 42 K, the ferrimagnetic ordering temperature of Mn3O4. Above 42 K, Hr is temperature-independent, but ΔH shows noticeable changes near 102 and 118 K (TN for MnO). From the observed change in g below 42 K, an anisotropy of 90 Oe for Mn3O4 in MnO is determined and this anisotropy is consistent with the observed ΔH. This anisotropy, about 10−2 times the anisotropy of pure Mn3O4, may be primarily due to exchange anisotropy at the Mn3O4–MnO interface.
A microwave instability with 1 μW holding power
Authors: Barberis D. , Waldner F. , Arend H.
Published: February 2003

Microwave instabilities have been found by parallel pumping in a layered antiferromagnetic (NH3–(CH2)2–NH3)CuCl4 which has ferromagnetic interactions within the layers. Above rather small microwave power levels, strong absorption signals appeared at resonance conditions for half the applied frequency below and above the spin-flop field Hsf. The threshold conditions are extremely sensitive to the orientation of the static magnetic field along the easy axis. The signal below Hsf has a distinct hysteresis, and its threshold of the microwave field is proportional to T3. Such a behavior has been predicted by Harris et al. for uniaxial antiferromagntics; however, the observed threshold field is more than one order of magnitude lower. Above threshold, the instabilities are composed of several steps which are sample dependent. Moreover, an instability has been found at resonance conditions for the creation of four magnons.