bluuebunny/crossref_metadata_2025 huggingface dataset:
Holographic grating formation in photorefractive crystals with arbitrary electron transport lengths
Authors: Moharam M. G. , Gaylord T. K. , Magnusson R. , Young L.
Published: February 2003

The time development of optically induced refractive-index hologram gratings in photrefractive electro-optic crystals such as lithium niobate and bismuth silicon oxide is analyzed allowing arbitrary electron-transport lengths and nonsinusoidal grating shapes. In this analysis, diffusion and drift in applied and space-charge fields as well as the bulk photovoltaic effect (when applicable) are included. Results for the photoinduced space-charge field are presented for a range of realistic experimental conditions. It is shown that the spatial phase of the space-charge field and therefore the beam coupling is strongly dependent on the electron-transport lengths, whereas the magnitude of the field and therefore the diffraction efficiency is not dependent. It is shown that for paraelectric materials (such as BSO) the results of short- and long-transport-length analyses must converge for long recording times (saturation).
Temperature-stimulated acoustic emission in the niobium-hydrogen system
Authors: Cannelli G. , Cantelli R.
Published: February 2003

The hydride precipitation in the Nb-H system has been studied by the acoustic-emission technique varying the temperature between 330 and 225 K at hydrogen concentrations ranging from 3.8 to 5.8 at.%. Concomitantly, elastic-modulus and internal-friction measurements have been conducted in order to reveal the hydride-precipitation temperatures and the plastic-deformation phenomena occurring during the formation of the hydride misfitting precipitates. In the virgin material, acoustic emission is absent during evolution of the precipitation although the dislocation-multiplication processes are operative. When, due to a severe precipitation, a certain degree of deterioration of the material has been reached, acoustic activity characterized by discrete bursts is then stimulated by the hydride formation and definitively persists also after the high-temperature annealing. The temperatures of the onset of the acoustic emission are lower than those corresponding to the hydride precipitation and may fit a line parallel to solvus. The data clearly indicate that neither the phase transformation per se nor the plastic-deformation processes accompanying the precipitation can be the sources of the observed acoustic emission. The results suggest that the measured emissivity may be attributed to the nucleation and growth of nonrecoverable defects. According to the proposed model, during hydride precipitation, acoustic-emission activity should be detected when a progression of irreversible deterioration of the material is occurring.
Electron-beam propagation in plasma channels
Authors: Freeman J. R. , Poukey J. W.
Published: February 2003

Electron beams propagating in current-carrying plasma channels proposed for ICF reactors generate an electric field which drives a return current. This electric field reduces the electron energy and also causes an expansion of the trajectory envelope. The scaling of this effect is discussed and estimates of its importance for reactor-level conditions are presented.
Fusion cross sections and thermonuclear reaction rates
Authors: Peres Asher
Published: February 2003

Experimental data for five fusion reactions of D, T, and 3He below 1 MeV are reviewed. Analytical formulas are given for the reaction rates as functions of the temperature, up to kT=100 keV. These formulas depart appreciably from some currently used when kT<3 keV.
Slow space-charge wave propagation on a relativistic electron beam
Authors: Gammel G. , Nation J. A. , Read M. E.
Published: February 2003

A description is presented of an experimental study of the growth and propagation of a large-amplitude slow space-charge wave on a weakly relativistic electron beam. The wave is grown as a result of an unstable interaction between a slow space-charge wave on the electron beam, and the TM modes of a periodic waveguide. Following wave growth the modulated beam is propagated through a cylindrical waveguide. Experimental results show that we have grown, and can propagate, a coherent wave, having a peak electric field of 60 kV/cm, with a phase velocity of 0.29c. The results presented have application to the collective acceleration of ions in intense relativistic electron beams.
Magnetic characterization of semi-amorphous dispersions of nickel on alumina-graphite substrates
Authors: Yamamura Hiroshi , Mulay L. N.
Published: February 2003

We report the characterization of two catalysts containing (I) 44 and (II) 57.3 wt. percent of Ni dispersed on Al2O3, containing a graphite binder. It is shown that magnetization (σ) versus H/T curves provide not only an analysis of very small (<100 Å) catalytically active particles, but also provide clues to the changes in particle profiles (size and shape) during the sintering of Ni dispersions. The conglomeration of the superparamagnetic (single-domain isotropic) particles to ’’needle’’ shaped (single-domain anisotropic) particles is analyzed in terms of the corresponding changes in the coercive force. Catalyst (I) with its lower nickel loading was found to be more thermally resistant to the formation of the multidomain particles over the entire HTT range. Work in progress on correlating the electronic parameters of Ni with its catalytic activity is outlined.
Inhomogeneities in bubble films measured by spin wave resonance
Authors: Robertson J. M. , Algra H. A.
Published: February 2003

After a brief review on the use of spin wave resonance as a tool used to study the magnetic properties of liquid epitaxial garnet layers an example is given for CaGeSmLu:YIG films. A modified melt was used in which the Sm2O3 concentration was reduced. The main result is that the growth kinetics produce film growth rate changes that influence the incorporation of Ca and Ge ions. This results in structured layers consisting of a transient and a bulk layer in which the anisotropy fields Ku/M are different. The change of Ku/M of the transient layer during film growth is interpreted in terms of a solid state diffusion process. The results of etch experiments are presented. Also values of the exchange constant A have been measured. Finally, growth conditions are estimated for homogeneous film growth.
Comparison of eight mixed garnet systems for 7 μm-period bubble devices
Authors: Makino H. , Hibiya T.
Published: February 2003

An extensive investigation of eight mixed garnet systems, totally 22 compositions with the same l values (0.2μm), was carried out for realization of high bit density bubble memory chips employing 1.8μm diameter bubbles in 7μm-period devices. The eight systems are YSmLuCaGe, YSmTmCaGe, YEuLuCaGe, YEuTmCaGe, YSmLuGa, YSmTmGa, YEuLuGa and YEuTmGa garnets grown on (111) GGG substrates. In order to fill in the material gap between Sm- and Eu-based garnets, YSmEuLuCaGe and YSmEuTmCaGe garnets were also studied. Comparison was made with respect to static (4πMs, Ku, HK, TC, A) and dynamic (μw, ϑ) properties, as well as Hco1 temperature dependence. Q-factor was varied by changing rare earth content ratio, but l and film lattice parameters were left essentially unchanged. From the dynamic and temperature properties viewpoints, it was revealed that YSmLuCaGe, YSmTmCaGe, EuLuCaGe, YSmEuLuCaGe, and YEuTmGa garnet systems are candidate materials, with l=0.2μm and Q?4, for practical applications which utilize 7μm-period patterns.
Epitaxial small magnetic bubble La–Sm–Lu iron garnet films grown on NdGaG substrates oriented (100) and (111)
Authors: Giess E. A. , Kobliska R. J. , Cardone F.
Published: February 2003

A Sm2.48Lu0.26(Pb,Pt)Fe5O12 garnet film composition grown earlier1 by LPE on NdGaG substrates oriented (100) and (111) is now diluted (in steps) to 56 mol% of a hypothetical La1.35Lu1.7Fe5O12 garnet. Most of the results reported are for films grown at 830 °C, but the effects of changing growth temperature for the compositions with the largest La–Lu substitutions are also discussed. La–Lu substitutions in fluxed melts significantly decrease film growth rates, and La must be present in melts in amounts in excess of those desired in the final crystal film. Both Pb from the fluxed melt and Pt from the crucible via the melt are incorporated into films in minor quantities. The ratio of rare earths and Pb to Fe and Pt in films is greater than the stoichiometric 0.6. The films support bubbles in the 0.5μm diameter range and have characteristic length l values of 0.037 to 0.062μm. Saturation magnetization values are 1700 to 2000 g (×10−4T). Domain wall damping coefficients are reduced in proportion to the amount of Sm replaced. The g factor is about 2 for all the films. The l, magnetic anisotropy Ku, and stability factor Q are decreased by La–Lu substitutions for (100) films, but they are first increased slightly then decreased for (111) films. With the largest La–Lu substitution, (100) films have zero Q. The highest l, Ku [3.6×105 erg/cm3 (×10−1 J/m3)] and Q (2.5) exist for (100) films with no La.
Growth and properties of Sb and Ti substituted (100) EuIG films as a function of Pb content
Authors: Plaskett T. S. , Klokholm E. , Cronemeyer D. C.
Published: February 2003

Films of (100) EuIG doped with Sb or Ca:Ti and (100) EuYIG doped with Sb were grown with various Pb contents from a PbO:5.5 B2O3 (mole ratio) based flux. The large Pb-induced uniaxial anisotropy, which occurs in (100) Pb:EuIG films was not reduced significantly by Sb or Ca:Ti additions. The l-parameter decreased from 0.07 for undoped films to about 0.04 to 0.05, for doped films at Pb contents between 0.6 and 0.8 moles/formula unit. These data suggest that Sb and Ti had substituted for the octahedral Fe and had increased the magnetization. The Q-factor for films with these l-parameters was about 2. It is further assumed that Pb is incorporated as Pb2+ and Pb4+ on different cation sites according to the model of Scott and Page. A comparison of our calculated and measured values of Δa support this model.
Estimation of growth induced order parameter in bubble domain films from coercive force measurements
Authors: Walling J. C.
Published: February 2003

A positive dependence of bubble domain coercive force on inverse film thickness has been attributed to coercivity associated with the film substrate interface [E. B. Moore, B. A. Calhoun, and K. Lee, J. Appl. Phys. 49, 1879 (1978)]. An alternate quantitative explanation is offered that is based on the distribution statistics of ions which possess large single ion magnetic anisotropy. It is shown that the measured coercive force vs film thickness when considered together with magnetic anisotropy provides an estimate of the growth induced order parameter. The order parameters so computed, based on the data reported by Moore, Calhoun, and Lee [ibid.] and Vella-Coleiro et al. [G. P. Vella-Coleiro, F. B. Hagedorn, S. L. Blank, and L. C. Luther, J. Appl. Phys. 50, 2176 (1979)] are on the order of 5% which compares favorably with spin resonance measurements performed on Nd3+ in YAG [M. D. Sturge, S. L. Blank, and R. Wolfe, Mat. Res. Bull. 7, 989 (1972)]. It seems clear from this analysis that the proposed mechanism could be a major, if not dominant, source for the thickness dependence of coercive force.
Influence of planar domains on bubble velocity and stability
Authors: Suzuki Ryo , Sugita Yutaka
Published: February 2003

Dependence of bubble state stability and translational apparent bubble velocity on the direction of an in-plane field has been observed in Permalloy-coated garnet films. Bubble state stability and velocity are affected by the position of planar domains with respect to the direction of bubble motion. The position of the planar domain is determined by the direction of in-plane field. When the planar domains trail the bubbles, the bubbles move faster and the stable regions for bubble-wall states are larger than when the planar domains lead the bubbles. The difference in stable regions is caused by an increased mutual interaction between the bubble and the planar domain when the planar domain leads the bubble.
Velocity asymmetry during stripe head propagation in ion-implanted bubble garnet films
Authors: Gallagher T. J. , Humphrey F. B.
Published: February 2003

Stripe head propagation has been investigated in ion-implanted garnet films using high speed photography with 10 nsec laser pulse illumination. For a given in-plane field applied along the stripe, the stripe head velocity increases linearly with drive until a peak drive is reached, beyond which the velocity drops. The peak velocity increases with in-plane field magnitude and depends on which of the two directions parallel to the stripe that the in-plane field is applied. Numerical calculations of the dynamic wall structure are made to predict the peak velocity as a function of in-plane field magnitude and direction. The effect of the implanted layer is taken into account by using a surface pinning condition. Results show that velocity breakdown occurs when a horizontal Bloch line (HBL) is nucleated. The velocity asymmetry with respect to in-plane field direction occurs because the HBL nucleates at opposite surfaces for the two in-plane field directions. The implanted layer inhibits HBL nucleation by pinning the surface spins, thus producing a higher peak velocity.
Abstract: Irreversible rotation processes in uniaxial ferromagnetic crystals
Authors: Asti G. , Bolzoni F.
Published: February 2003

The coexistence of two minima in the anisotropy energy of a ferromagnetic crystal allows irreversible rotations of the magnetization vector to occur at a critical value Hcr of the applied magnetic field. These first order magnetization processes (FOMP) are in fact similar to the spin reorientation transitions that take place between different easy directions with changing temperature. The study of FOMP allows precise determinations of the anisotropy constants to be carried out if one knows the relations with the critical parameters. Previous papers give experimental evidence of FOMP in ferrites1 and intermetallic2 compounds together with a preliminary theoretical treatment. In the present work we carry out a complete analysis of this phenomenon in terms of the first three anisotropy constants Ki and coefficients κ21,0, for a uniaxial crystal with field applied parallel or perpendicular to the symmetry axis. Analytical solutions have been found for the case of type 2 FOMP (when final state is below saturation) and for the boundary lines in the phase diagrams of easy directions and FOMP. Computer plots of the critical parameters vs. K2/K1, K3/K1 and x4,0/x2,0, x6.0/x2.0, and application to the FOMP observed at 16 Tesla in the easy cone crystal PrCo5 will be presented.

1G. Asti et al, IEEE Trans. MAG. 14, 883 (1978).

2D. Melville et al, IEEE Trans. MAG 12, 1012 (1976).
The effect of diffuse surface scattering of carriers on the calculated transmission of 24 GHz radiation through a ferromagnetic metal slab
Authors: Cochran J. F. , Heinrich B.
Published: February 2003

Numerical calculations of the magnetic field dependence of the transmission of 24 GHz radiation through a 5 μm thick slab for a model ferromagnetic metal have been carried out using a non-local relation between current and electric field, and using the Landau-Lifshitz equations to describe the magnetization. A spherical Fermi surface corresponding to carriers having an effective mass ratio of 5.0 and mean free paths of 10.8 μm was used to represent the electrical response of the metal. For diffuse scattering of the carriers at the slab surfaces the transmission was found to be strongly peaked at the value of static field which corresponded to ferromagnetic resonance (FMR). This result suggests that the anomalously large transmission structure observed at FMR in pure nickel single crystals at helium temperatures1 is an orbital effect due to the long mean free path of the current carriers.
Submillimeter ESR experiments using pulsed high magnetic field
Authors: Motokawa M. , Kuroda S. , Date M.
Published: February 2003

A new method has been developed at Osaka University for producing a mega-gauss field without destruction of the coil. As one of the applications of this system, submillimeter ESR experiments have been done at low temperatures by using HCN (λ=337μm) and H2O (λ=119μm) lasers in a field up to 0.5 MOe. We report some novel high field effects observed in these experiments. The g-shift due to the SH3 term is expected to be appreciable in such a high magnetic field. This effect was found in a study of Co-Tutton salt at 77 K. The experimental result showed 2% smaller g value at 119 μm than at 337 μm. This was explained quantitatively by an extensive calculation based on the Abragam-Pryce theory. So-called exchange splitting was observed in (NH4)  2CuCl4⋅2H2O, Cu(NH3)  4SO4⋅H2O (CTS) and CuCl2⋅2H2O. At 4.2 K the two observed lines were of quite different intensities and the weaker one showed a remarkable shift. These phenomena can be explained successfully by molecular field theory, and it is shown from the direction of the shift that the exchange interaction between inequivalent spins is antiferromagnetic for CTS and ferromagnetic for the others.
Measurements of a 70 T pulsed magnetic system with long operational life
Authors: Olson N. Thomas , Bandas J. , Kolb A. C.
Published: February 2003

A pulsed, high current machine has recently been developed for producing pulsed magnetic fields in the 70 Tesla range, with long operational life of the load inductor. The current source, which drives a single-turn solenoid, is a high voltage, low inductance capacitor bank. Connections from the capacitor bank to the inductor are by way of low inductance multichannel rail spark gap switches and low inductance buswork. Peak magnetic fields of 72 Tesla have been measured in the bore of the single-turn inductor. These measurements have been made using the magneto-optical, Faraday, effect. The pulsed magnetic machine has recently been used to develop enclosure welds on tubing which is being evaluated as possible cladding material in nuclear reactors.
Theory of light scattering by spin waves
Authors: Camley R. E. , Mills D. L.
Published: February 2003

Recent light scattering experiments probe the surface response of ferromagnets in the regime where both exchange and dipolar interactions are important. We discuss the theory for the response of a semi-infinite ferromagnet in this region within a continuum theory. We study the spectral density of surface spin fluctuations. This is used to calculate light scattering from spin waves. The light scattering spectra contain features resulting from interactions with both bulk and surface magnons. Our calculations give a good account of the experimental data reported for EuO and Fe.
Magnetization and magnetoresistance study of amorphous FexPd82−xSi18
Authors: Dublon G. , Lin C.-H. , Bevk J.
Published: February 2003

We find that amorphous FexPd82−xSi18 undergoes a transition from spin glass (x≲5) to ferromagnetic (x?25) through an intermediate state (x?10 –20). In Fe25Pd57Si18, magnetic order persists at room temperature. The importance of spin fluctuations in the spin glass, intermediate and ferromagnetic regimes is indicated by the negative magnetoresistance at 4.2 K which does not saturate up to ∼230 kOe.
Transmission of 24 GHz radiation through Co-P from 4 °K to 414 °K
Authors: Baartman R. A. , Heinrich B. , Cochran J. F. , Chi G. C.
Published: February 2003

The technique of ferromagnetic antiresonance microwave transmission1 at 24 GHz was used to study the magnetic properties of the amorphous ferromagnet, Co-P (∼25 at.%P), from 4 to 414 °K. The resulting data were used to obtain the saturation magnetization, g-factor, and the Landau-Lifshitz damping parameter, λ. The magnetization was found to obey the Bloch T3/2 − Law over the interval 4–79 °K. The g-factor and λ were found to be slightly temperature dependent. This temperature dependence is shown to indicate the presence of uniaxial anisotropy. The possible origin of this anisotropy is discussed.
Dragging of domains by a temperature gradient in ferromagnetic metals
Authors: Berger L.
Published: February 2003

A temperature gradient normal to domain walls generates an eddy current running around each wall. The magnetic fields of the various eddy-current loops have the right direction and sense to exert forces pushing all walls in the direction of the gradient. If the gradient exceeds a certain value, all walls will start moving in that direction. This ’’thermal domain drag’’ is similar to the domain-drag effect recently predicted and observed in ferromagnets traversed by an electric current, except that the eddy currents are caused by the Nernst-Ettingshausen effect rather than by the Hall effect. When the walls move, the observed thermoelectric voltage will not be proportional to the temperature gradient anymore. This is similar to the failure of Ohm’s law predicted and observed in ferromagnets traversed by a current. While a uniaxial magnetic anisotropy is required for domain drag, thermal domain drag can be achieved even in isotropic or cubic materials. Numerical estimates suggest that the proposed experiment should be possible in low-coercivity materials at room temperature or above, as well as at low temperature. The inverse effect exists too: moving walls generate a heat flux parallel to their direction of motion.
Magnetization dependence and temperature dependence of the magnetic anisotropy in iron whiskers near Tc
Authors: Hanham S. D. , Heinrich B. , Arrott A. S.
Published: February 2003

The magnetic response of an iron whisker grown with its long axis parallel to the [111] direction has been measured up to and through the Curie temperature. The anisotropy constant is found from the response in the range of fields between that necessary to bring the magnetization in the central cross section of the whisker to Ms/sqrt(3) and that to reach Ms. We extract a field proportional to K1/Ms and analyze its dependence on Ms and on temperature. The results indicate that K1/Ms∼Msn with n=3.11±.05 for the temperature range 0.0005< (Tc−T)/Tc<0.002 with n increasing at lower temperatures. The sensitivity of the method permits the extraction of K1 values over five orders of magnitude.
Magnetostriction of some rare earth-aluminum Laves phase compounds
Authors: Pourarian F. , Wallace W. E.
Published: February 2003

Anisotropic magnetostriction measurements of some R-Al2 (R=Gd, Dy, Ho and Er) compounds have been carried out from 4.2 K up to their Curie temperatures (Tc). Magnetic fields (H) up to 2.5 Tesla were applied. The extrapolated (to 1/H=0 for H≳1.4 Tesla) saturation magnetostrictions determined at 4.2 K are 17×10−6, −1420×10−6, 60×10−6 and −920×10−6 for GdAl2, DyAl2, HoAl2 and ErAl2, respectively. A dramatic reduction in the magnitude of the strain observed for HoAl2 below 15 K may be associated with a change of easy direction of magnetization. For GdAl2, the strains observed above the saturation are found to be strongly field-dependent. The temperature dependence of magnetostriction for DyAl2 is interpreted in terms of the Callen and Callen’s single-ion model. Large volume strains are obtained for these compounds (except for GdAl2). An attempt is made to estimate the anisotropic volume constant h3 at 4.2 K.
Susceptibility and specific heat of insulating Magnéli phases VnO2n−1
Authors: Nagata S. , Griffing B. F. , Khattak G. D. , Keesom P. H.
Published: February 2003

The magnetic susceptibilities and the specific heats of single crystals of the vanadium Magnéli phases VnO2n−1(3?n?8) have been measured at low temperatures. Magnetic and thermodynamic properties associated with the antiferromagnetic ordering in the insulating state are strongly affected by spin pairing of vanadium ions. The Néel temperature TN is lowered rather smoothly with increasing n, which corresponds to larger spin pairing effects. A large short range order effect was observed in V3O5, which has no spin pairing. The susceptibility and the specific heat show the behavior of a low dimensional spin system. For V4O7 and V6O11 the magnetic entropy changes up to TN are less than 20% of the value R1n(2S+1) which would be expected if spin pairing were absent; this indicates considerable spin singlet pairing. On the other hand, V7O13 does not display a metal-insulator transition and remains metallic down to 1.2 K. Some remarkable features were observed for V8O15 in the susceptibility and the specific heat. These results suggest that the transition at low temperature (6.1 K) is not an ordinary antiferromagnetic one but another type of transition.
A neutron diffraction study of the structure of the antiferromagnet CopNi1−pO
Authors: Battle P. D. , Cheetham A. K. , Gehring G. A.
Published: February 2003

We have carried out neutron diffraction measurements on polycrystalline samples of CopNi1−pO with p=0.03, 0.1, 0.2, 0.33, 0.5, 0.6, 0.8.
Magnetic properties and corrosion resistance of (CoFeB)100−xCrx thin films
Authors: Brunsch A.
Published: February 2003

In order to improve the corrosion resistance of sputtered Co79Fe6.5B14.5 amorphous thin films, which were found to have magnetic properties superior to those of permalloy films with respect to magnetic device applications, up to 15 at.% Cr was alloyed to the Co74Fe6B20-target material. The resultant compositions of the r.f. bias sputtered films were (Co79Fe6.5B14.5)100−xCrx with x up to 15 at.%. As deposited films exhibit an increasing amount of perpendicular anisotropy with increasing Cr-content, which could not be reduced by hard axis field annealed at 250 °C. Anisotropy fields as high as 1000 Oe were measured parallel to the film plane. The dependence of the saturation magnetization, of the electrical resistivity, and of the coercivity on the Cr-content as well as the formation of the strong perpendicular anisotropy indicates that a transition from the amorphous to a microcrystalline state occurs mainly between 4 and 7.5% Cr. Due to the crystallization which is not detectable by x-ray diffraction, the corrosion resistance of CoFeB could not be improved by the addition of Cr.
Effect of silicon addition on the magnetic properties of Fe-B-C amorphous alloys
Authors: Mitera M. , Masumoto T. , Kazama N. S.
Published: February 2003

The effect of compositions on the saturation magnetization, Curie temperature and coercivity of the amorphous Fe-B-C alloys has been investigated in a wide range of B and C concentration. The C addition less than 7 at.% to Fe-B alloys increases the saturation magnetization at the room temperature. The highest magnetization, σs = 178 emu/g, with the lowest coercive force, Hc = 22 mOe, has been obtained for the Fe81B12-C7 alloy annealed in a magnetic field. In order to obtain further desirable soft magnetic properties, the effect of the addition of other elements to the Fe-B-C based amorphous alloys has been studied. The best properties are σs (R.T.)  = 176 emu/g, Hc = 8 mOe, Br/B100 = 0.88 and the core loss W/f = 8×10−4 watt. sec/kg (at 12.5 kG and 50 Hz) for the magnetically annealed Fe81B13C2Si4 alloy. As a result, it has been found that the addition of Si is most effective in reducing the coercive force and core loss as well as an improving the magnetic stability during aging at low temperatures.
Compatibility of dc and ac magnetic properties of amorphous magnetic materials
Authors: Shirae K.
Published: February 2003

This paper reports dc and ac magnetic properties of amorphous Fe40Ni38-Mo4B18 (METGLAS : 2826MB) annealed at various temperatures. DC coercive force showed minimum and squareness ratio reached almost unity annealed at about 350 °C, however, ac permeability turned out extremely low. High permeability has been obtained by annealing above 400 °C at the cost of increase of dc coercive force and decrease of squareness ratio. Nonlinear and hysteretic changes of permeability against ac magnetic field have been observed in materials annealed below 380 °C and as-quenched materials. These defects have been overcome by annealing above 400 °C. Disaccommodations, which are very large in materials annealed below 380 °C, have disappeared also when annealed above 400 °C.
High-energy spectroscopy of fn+1 and fn−1 states in rare earth metals
Authors: Baer Y. , Lang J. K.
Published: February 2003

Two different spectroscopies have been used to study the 4f shell in rare earth metals. The spectra obtained by X-Ray Photoemission Spectroscopy (XPS) reflect the final states resulting from the transitions fn→fn−1; in Bremsstrahlung Isochromat Spectroscopy (BIS) the recorded intensity of x-rays accounts for the transitions fn→fn+1. The analysis of the two types of spectra of one element with initial configuration 4fn yields an exact determination of the excitation energies Δ− and Δ+ to the ground states of fn−1 and fn+1. The experimental energies are related to EF and correspond to completely screened final states of the metals. (Δ+−Δ−) can be interpreted as the screened Coulomb correlation energies U which is very large in these metals (5–12 eV) and prevents the formation of a band.
Heat capacity studies of RFe2 intermetallic compounds (R=Ho, Er, and Lu)
Authors: Germano D. J. , Butera R. A. , Sankar S. G. , Gschneidner K. A.
Published: February 2003

Rare earth intermetallic compounds possess crystal field interactions which can be observed as contributions to the heat capacity. This paper reports the results of heat capacity studies of several RFe2 compounds (R=Ho, Er, and Lu). The crystal field contributions to the heat capacities for the Ho and Er ions, determined from the heat capacity data obtained for HoFe2 and ErFe2, have been used in determining the crystal field parameters for these rare earth ions. In our case, for Er3+, B40=1.937×10−3 K and B60 =−1.195×10−5 K; and for Ho3+, B40=−9.40×10−4 K and B60=5.10×10−6 K. These parameters are discussed and compared to those obtained by neutron diffraction and spin reorientation studies.
Magnetic field and temperature dependence of the velocity of sound in Tb.3Dy.7Fe2
Authors: Melamud M. , Hathaway K. , Cullen J.
Published: February 2003

Measurements of the velocity of sound in Tb.3Dy.7Fe2 as a function of magnetic field and temperature are reported. The magnetic field dependence is compared with a calculation of the change in elastic moduli of a random array of crystallites which are magnetoelastically coupled to the sound field. Comparison is also made with measured sound velocity changes with field in amorphous alloys of the R-Fe type.
Hyperfine fields in Sm1−xGdxAl2 alloys—Microscopic evidence for ferromagnetic coupling between rare earth spins
Authors: Grover A. K. , Malik S. K. , Vijayaraghavan R. , Shimizu K.
Published: February 2003

The results of hyperfine field studies on Sm1−xGdxAl2 alloys for 0?x?0.5 are reported. The hyperfine field at Al, H(Al), has been measured to be +32.5 kOe in SmAl2 and −47 kOe in GdAl2. In Sm1−xGdxAl2 alloys, we find that the magnitude of H(Al) increases with increasing x and further H(Al) becomes negative even with small replacement of Sm by Gd. H(Al) in these compounds is proportional to the average value of spin per rare earth ion. The observed behaviour can be understood in terms of a ferromagnetic coupling between the spins of Sm and Gd.
Hall effect in 3d-transition metals and alloys (invited)
Authors: McAlister S. P. , Hurd C. M.
Published: February 2003

We concentrate on the Hall effect in magnetic 3d-metals, which shows an anomalous component varying nonlinearly with applied field. Its origin is spin-orbit coupling, and its manifestations are described as characteristic electron scattering processes: skew scattering and side-jump displacement. We shall consider these features as they appear for scattering by isolated 3d ions in paramagnetic alloys, and for scattering in the ferromagnetic 3d metals.
First and second order transitions in some metallic ferromagnets
Authors: Wohlfarth E. P.
Published: February 2003

Second order transitions are discussed for compounds of the heavy rare earths and yttrium with cobalt. The calculated Curie temperatures agree well with those observed and an analogy is established between the effect of rare earth additions and of pressure. First order transitions in critical fields and at critical temperatures occur in some of these compounds. The effects of magnetoelasticity on such transitions are investigated by reformulating the Bean-Rodbell theory of 1962 in itinerant electron terms. It is found that in general these effects are smaller than those arising from the itinerant electron character itself, meaning the temperature dependence of the Landau coefficient B of M4 which is completely different from the Bean-Rodbell case.
Temperature dependence of hyperfine fields at nonmagnetic impurities in ferromagnetic metals
Authors: Meier P. F. , Denison A. B.
Published: February 2003

A model for the spin densities at dilute non-magnetic impurities in ferromagnetic host metals is presented which predicts generally a non-linear dependence of the hyperfine field on the host magnetization. The influence of lattice vibrations on the transferred hyperfine field is considered and the results of specific calulations are presented.
Abstract: Fermi surfaces and single particle excitations in itinerant ferromagnets
Authors: Lonzarich G. G.
Published: February 2003

Recent experimental investigations of the Fermi surfaces of the 3d ferromagnets, as a function of pressure and temperature, are discussed in relation to models of the ground and low-lying excited states of itinerant-electron ferromagnets. Attention is focused on studies of the ground-state Fermi surface of Fe and on the contribution of single-particle spin-flip (Stoner) excitations to the temperature dependence of the Fermi surfaces of Fe, Co and Ni at low temperatures. It is shown in particular that the experimental information derived from the de Haas–van Alphen effect, neutron inelastic scattering, and bulk magnetization measurements would suggest that the temperature dependence of the magnetization in Ni cannot be adequately understood solely in terms of conventional spin-wave and Stoner excitations in the low temperature regime (T≲20 K). An investigation of the low energy magnetic excitations in the weak itinerant ferromagnet Ni3Al, by means of small angle neutron scattering and magnetization measurements, is also discussed.
Abstract: Migdal-like approximation for quantum spin systems
Authors: Barma Mustansir , Kumar Deepak , Pandey Ras Bihari
Published: February 2003

We study the consequences of recently proposed recursions [1] for the anisotropic spin-1/2 Heisenberg model, based on a generalization of the Migdal approximation [2]. In the isotropic case [3], they give the correct lower critical dimension, 2, and yield ν=1/ε in (2+ε) dimensions as ε→0. In three dimensions, ν=1.40 and φ=1.56. The recursions give a finite entropy and linear specific heat as T→0. They give a reasonable description of Ising-like anisotropy, but a strange and qualitatively incorrect picture of the XY side: first, there is no XY fixed point (fp) at T=0, and in three dimensions a flow from the finite-T XY fp leads to the T=0 Heisenberg fp. Second, there is a jump (as opposed to flow) behaviour in the first iteration of any point in a large region of the anisotropy-temperature plane. Third, the finite-T fp persists in fewer than 2 dimensions, and a new finite-T XY fp also appears; both are spurious. We also study the sensitivity of the results on b, and find that unlike the Migdal approximation for classical systems, here even the lower critical dimension in the isotropic case depends on b.
Neutron scattering observation of solitons (invited)
Authors: Steiner M.
Published: February 2003

It has been suggested that in systems with strong fluctuations as around a critical point strongly nonlinear effects should occur. The simplest possible equation for nonlinear dynamics is the sine-Gordon equation. This equation can be applied to the dynamics of a 1-D-ferromagnetic chain with planar anisotropy in a symmetry-breaking field (magnetic field perpendicular to the chain direction). The dynamics of such a system consist of two types of elementary excitations: nonlinear modes (solitons and breathers) and linear modes (spin waves). The thermodynamics for the nonlinear modes are the same as for a gas of noninteracting relativistic quasi-particles. In the frame of that picture the dynamic structure factor for an inelastic neutron scattering experiment can be calculated for the relativistic case, and it appears that inelastic n-scattering is the most direct way for the observation of solitons. Experimental results, obtained for CsNiF3 are discussed and compared with the theoretical results. These experimental results show that nonlinear modes are indeed an essential part of the dynamics of that system.
Quantum effects in the spin dynamics of the linear Heisenberg antiferromagnet
Authors: Müller Gerhard , Beck Hans , Bonner Jill C.
Published: February 2003

We present an approximate analytic expression for the dynamical spin correlation function of the S=1/2 linear Heisenberg antiferromagnet at T=0. The basis for our approach is that in zero field the spectrum is dominated by a double continuum [in (q,ω) -space] of triplet spin wave excitations. The S=1/2 integrated intensity agrees very well with recent neutron scattering results on CPC, unlike the corresponding classical intensity. Moreover, the S=1/2 spectral weight function shows increasing asymmetry as q→π, a quantum effect, observable in more recent neutron scattering data. In non-zero magnetic field, there exist two, partly overlapping, double continua, each giving rise to a peak situated at the lower boundary. The (zz component of) spectral weight function therefore has a double-peaked structure, as observed experimentally. Theory and experiment are in apparent agreement concerning the energy difference between the peaks.
Bloch wall spin waves
Authors: Lévy J. C. S.
Published: February 2003

According to a simple model of Hamiltonian, the bound spin wave of a 180° Bloch wall has a zero frequency. Recent observations show a non zero frequency for this mode. Here we account for the different perturbative terms as we try to solve the complete equations of motion of the magnetization components, i.e. a Dirac-like equation. An exact general resolution A is sketched, a perturbative treatment B with step potential is used and at last an exact solution C valid in a lot of cases is derived. One main result is the existence of a non zero frequency bound mode shown by B and C which corresponds to the Döring formula of the wall resonance energy.
Electronic structure of magnetic 3d metals: Ground state, Fermi surface and photoemission properties
Authors: Eastman D. E. , Janak J. F. , Williams A. R. , Coleman R. V. , Wendin G.
Published: February 2003

We describe various electronic and magnetic properties of the ferromagnetic 3d metals Ni, Co and Fe and related metals, including ground-state properties, Fermi surfaces and both one-electron and many-electron aspects of photoemission and optical absorption processes. Experimental de Haas-Van Alphen results for the spin-polarized Fermi surfaces and angle-resolved photoemission results for the exchange-split energy-band dispersions for Ni, Co and Fe are summarized. Single-particle energy-band descriptions of these Fermi surfaces and band dispersions, as well as various ground-state properties (lattice constant, cohesive energy, bulk modulus, magnetic moment, hyperfine field, etc.) are given in terms of the density-functional theory of Hohenberg, Kohn and Sham. In general, these properties can be understood quite well within the single-particle picture. Also discussed are troublesome questions concerning the exchange splitting, band dispersions and satellite structure of Ni. Various optical and photoemission processes for Co, Fe, Ni and Cu exhibiting many-electron phenomena are discussed, including four-level absorption edges, resonances, photoemission relaxation effects, shake-up processes and Auger processes.
Spin dynamics of mixed-valent rare-earth compounds
Authors: Loewenhaupt M. , Holland-Moritz E.
Published: February 2003

A survey is given on the dynamical behaviour of homogeneous mixed-valent compounds as observed from magnetic neutron scattering experiments. Mixed-valent compounds are characterized by the existence of two nearly degenerate electronic configurations for the rare earth ion with integer occupation numbers of the 4f shell. From XPS- and Mössbauer effect measurements a lower (10−15 sec) and an upper (10−9 sec) limit for the lifetime of both configurations (involving charge fluctuations) can be estimated. From the neutron scattering experiments we learn that in these compounds there are also very fast spin fluctuations of the order of 10−13 sec. The characteristic differences in the dynamical behaviour of compounds with a magnetic and a nonmagnetic configuration (Ce and Yb compounds) and a compound with two magnetic configuration (TmSe) will be discussed.
Optical reflectivity and possible origin of the magnetic red shift in ferromagnetic CdCr2Se4
Authors: Zvara M. , Schlegel A. , Wachter P.
Published: February 2003

The specular reflectivity of CdCr2Se4 single crystals has been measured within the spectral energy interval 0.03 eV–12 eV at room temperature. The spectral dependence of the real and imaginary part of the dielectric constant has been obtained from a Kramers-Kronig analysis of the experimental data. From an ionic model of the spinel structure using the Born-Haber cycle the energies of the various bands and localized levels have been derived also as a function of the structure parameter u. This now enables a comparison of the optical absorption with calculated energy differences. Furthermore, the results of the pressure shift of the absorption edge and the compressibility are used to reduce the possibilities of electronic transitions at the absorption edge. For the magnetic red shift in the Cr spinels a new mechanism is proposed involving the observed dependence of the structure parameter u on the magnetic order.
Faraday effect dispersion in nickel and permalloy thin films
Authors: Brin M. , Juretschke H. J.
Published: February 2003

Faraday rotations in nickel and permalloy films up to 80-20 Ni-Fe compositions have been obtained at both normal and oblique incidence. Incident light was parallel to the magnetic field which ranged up to 8 kilogauss. For oblique incidence a graphic analysis of Faraday rotation vs. applied field yields both the magnetization and specific rotation. The dispersion curves for both the nickel and the permalloys show rotations which increase in moving from higher to lower energies in the range 0.7 to 3.0 eV. Rotation peaks occur at 1.2 eV for the nickel and at 1.7 eV for 80-20 permalloy. We identify the peak in nickel with that shown in earlier MOKE conductivity measurements. Identical structure with shift to higher energies is exhibited by the permalloys. We attribute the shift primarily to an equivalent lowering of the Fermi level as iron is added to the nickel.
The volume dependence of the Curie temperature and magnetization of Pd-Mn alloys
Authors: Guy C. N. , Ström-Olsen J. O.
Published: February 2003

Large negative pressure derivatives of Tc, M(0,0) found for Pd1−xMnx (.014 < x < .04) are interpreted in terms of weak itinerant ferromagnetism.
High pressure study of PdFeMn
Authors: Wu M. K. , Aitken R. G. , Chu C. W. , Huang C. Y. , Olsen C. E.
Published: February 2003

Dilute magnetic alloys of PdFeMn have been investigated up to ∼20 kbar, demonstrating that the mechanism for the kneelike sharp rise in the low-field ac susceptibility χ on cooling is different from that for the reversed kneelike sharp drop of χ.
Spin flop in a spin glass
Authors: Coey J. M. D. , Roux-Buisson H.
Published: February 2003

Alloys in the system Ni.95 S Fe exhibit uniaxial anisotropy which is similar in magnitude to the exchange. Ni.95 S is a non-magnetic d-band metal and iron a magnetic impurity, so the system bears some resemblance to an Ising spin glass. Anisotropy modifies the magnetic properties as compared with a normal spin glass, giving a susceptibility more like that of an antiferromagnet. The maximum in χ ∥ at the freezing temperature Tf retains its form but shifts to lower temperature with increasing field. A sharp increase in the parallel magnetization below Tf in a large applied field is identified as spin flop of iron in the weakest exchange fields.
Some memories of developments in the theory of magnetism (invited)
Authors: Anderson P. W.
Published: February 2003

I discuss early work in magnetism at Bell Laboratories and then survey the ways in which the theory of magnetism has contributed important ideas and concepts to the theory of condensed matter.
Magnetic materials and applications– A quarter-century overview (invited)
Authors: Jacobs I. S.
Published: February 2003

The series of Conferences on Magnetism and Magnetic Materials, now 25 years old, has provided a successful meeting place for science and technology by deliberately bringing together physicists, engineers, chemists, and metallurgists interested in the subject. During this period new classes of magnetic materials, remarkable magnetic phenomena, many magnetic devices, and various new applications of magnetism have been discovered. This paper provides a sketch of some trends in magnetics research, particularly in materials and applications, along with recollections of the early conferences. An overview is presented of the continued developments in hard and soft magnetic materials and in a variety of magnetic memory/recording media. Included are some observations on a number of advances in materials and phenomena, also with applications potential, which did not reach the marketplace, and on relationships between exploration and goal-oriented programs. During this quarter century, information storage and processing technology has been a major stimulus for much magnetics RD, but we are now seeing some shift toward considerations of energy and resources conservation in electromagnetic devices and applications.
Panel discussion: Spin glasses
Authors: Guy C. N. , Tholence J. L. , Maletta H. , Thouless D. J. , Hertz J. A. , Kirkpatrick S.
Published: February 2003

After a brief review of recent low field experiments and the time evolution of magnetisation, new data on CuMn alloys is presented. The new data shows quite clearly that the spin glass temperature Tf does not mark the abrupt onset of irreversible behavior. Rather there is clear evidence for remanent magnetisation above Tf. Comparison with earlier a.c. susceptibility data suggests that there is a continuous freezing or blocking process occurring in the range of temperature centered on Tf.
Transition from ferromagnetism to spin glass ordering
Authors: Carnegie D. W. , Tranchita C. J. , Claus H.
Published: February 2003

Low field magnetization measurements on both weakly ferromagnetic and spin-glass like Ni-Cu and V-Fe alloys are presented. There is a qualitative difference between the two types of order in the temperature variation of the magnetization curves. In both cases the transition temperature Tc is signaled by a cusp in the a.c. susceptibility. For the ferromagnetic alloys, the height of the cusp is equal to the reciprocal demagnetization factor 1/N. For the spin glass alloys, the height depends on Tc itself: the smaller Tc, the lower the cusp. For both types of alloys, d.c. magnetization measurements reveal the onset of hysteresis at Tc. For the ferromagnetic alloys, the maximum slope of the hysteresis loop is equal to 1/N, independent of temperature for T?Tc. For the spin glass alloys, the maximum slope of the loop does not reach the 1/N limit at Tc, but continues to increase below Tc, almost reaching the 1/N limit at a lower temperature.