bluuebunny/crossref_metadata_2025 huggingface dataset:
Dependence of some properties on thickness of smooth amorphous alloy ribbon
Authors: Liebermann H. H. , Martis R. J. J. , Nathasingh D. M.
Published: February 2003

Smooth amorphous alloy ribbon, of nominal composition Fe80B14.5Si3.5C2, has been cast 2.54 cm wide in an average thickness range 13≤t̄≤80 μm. Since the ribbon samples made were largely devoid of underside liftoff areas (gas pockets), the properties measured are not affected by these surface asperities. Most ribbon of the present study has been cast on a copper-base wheel, while some has been made on a tool steel wheel. Magnetic, thermal, mechanical, and other measurements have been conducted as has x-ray diffraction of the upper and lower ribbon surfaces. Results indicate that properties characteristic of the amorphous state at first change rapidly and then more gradually with increased ribbon thickness. The limited number of ribbon samples cast on the tool steel wheel tend to exhibit greater brittleness but the same stress relaxation and Curie temperature as equivalent samples made on the copper-base wheel. Measured properties are discussed in terms of structural relaxation caused by average ribbon cooling rate differences resulting from the various sample thicknesses cast on the two substrate wheel materials. OFF
Effects of applied currents on domain structures and permeability in amorphous metal ribbons
Authors: Livingston J. D. , Morris W. G. , Jagielinski T.
Published: February 2003

The effects of applied currents were studied on amorphous ribbons of Co70.3 Fe4.7 Si15 B10 annealed to produce different values of transverse or longitudinal anisotropy. In transverse-anisotropy ribbons, current-induced domain-wall motion was studied by SEM and used to determine domain-wall surface energy and exchange constant for various values of anisotropy. In longitudinal-anisotropy ribbons, current-induced magnetization rotation was demonstrated by SEM. This magnetization rotation also produced an increased initial permeability, and the current to produce maximum initial permeability was found to be proportional to the anisotropy constant.
Hydrogenation and magnetic properties of amorphous rare-earth-iron (R-Fe) alloys
Authors: Schelleng J. H. , Forester D. W. , Lubitz P. , Vittoria C.
Published: February 2003

A novel film synthesis procedure is used to explore the amounts of hydrogen absorbed by amorphous a−R1−xFex alloys with 0≤x≤0.9 and R=Gd, Dy, Tb, Ho, Y. Magnetization and Mössbauer measurements on a-Gd1−xFex:Hy are illustrative of the dramatic magnetic changes produced by the hydrogen. For a-Gd1−xFex:H3 the compensation temperatures are reduced by about 200 K and the Curie temperatures by 50 K. Detailed analysis of magnetization M(T) data for a-GdFe2:Hy with y=0, 1.25, and 3.0 are presented to demonstrate the changes of magnetic moments and exchange parameters. JFe-Fe and JFe-Gd exhibit small percentage decreases with added hydrogen whereas JGd-Gd has a large change, going from ferromagnetic (y=0) to antiferromagnetic coupling (y=3). The iron moment increases by about 10%. The magnetic changes are interpreted in terms of charge transfer as mediated by anionic behavior of the hydrogen.
Magnetization and FMR studies in amorphous Fe90Zr10 and Fe70Ni20Zr10 ribbons
Authors: Krishnan R. , Rao K. V. , Liebermann H. H.
Published: February 2003

We report here our high field magnetization (in fields up to 15 T, and preliminary FMR studies on amorphous Fe90−xNixZr10 with x=0 and 20. The addition of Ni remarkably modifies the magnetic properties of Fe90 Zr10 alloy which can be summarized as follows: (1) The ferromagnetic transition temperature, TC, increases from 230 to 476 K; (2) While the magnetization in Fe90Zr10 does not saturate at 4.2 K for applied fields up to 15 T with a large susceptibility χhf ≂9×10−4 Oe−1, the substitution of Ni for Fe leads to an easy saturation for a field of 1 T, which is unusual for a random magnet; (3) At 4.2 K the magnetic moment of the alloy increases from 1.48μB to 1.6μB per atom, from which the magnetic moment of Fe in the Fe–Ni–Zr alloy is estimated to be 2.3μB/atom. The FMR line width in Fe90Zr10 increases monotonically with decreasing temperature. For the x=20 alloy, the line width is found to be about 160 Oe, and the value of g is found to be 1.94. These results suggest that interpretation of the properties of Fe–Zr alloys on the basis of weak itinerant ferromagnetism should be taken with caution.
Mössbauer spectroscopy study of amorphous Fe87B11Au2 ribbon and its crystallization products
Authors: Lin M. C. , Barnes R. G.
Published: February 2003

Substantial increases in Fe saturation magnetization have been obtained in amorphous Fe–B containing small concentrations of gold. This material is also stable above 300 K, and thus has considerable practical significance. We report the results of an investigation of amorphous Fe87B11Au2 ribbon and its crystallization products based on 57Fe Mössbauer spectroscopy. The amorphous ribbon exhibits a broad magnetic hyperfine splitting pattern typical of a metallic glass with an effective hyperfine field, Heff=257 kOe, and an isomer shift of 0.058 mm/s relative to metallic Fe at 300 K. The spectra of samples annealed for 25 min between TA=618 and 708 K arise from a metastable amorphous phase of Fe–Au–B and a crystalline α-Fe phase. Heff of the metastable amorphous phase decreases with respect to increased annealing temperature. However, Heff of the α-Fe phase increases from 331 kOe for samples annealed at 618 K to 334 kOe for those annealed at 708 K. This increase can be attributed to an increased content of Au in the α-Fe phase. Annealing the samples at temperatures above 753 K for 25 min yields crystalline α-Fe and the intermetallic compound Fe2B.
Effect of intraionic coupling on anisotropic interaction in actinide compounds: L-S and j-j coupling in Pu compounds (invited)
Authors: Thayamballi P. , Cooper B. R.
Published: February 2003

An interionic interaction arising from the hybridization of moderately delocalized f electrons with the band electrons is central in determining the magnetic behavior of cerium and light actinide monopnictides and monochalcogenides. Siemann and Cooper first recognized this in the case of the Ce3+( f 1) systems, and used the Coqblin–Schrieffer (CS) treatment of the hybridization for the f 1 ion in seeing how the Ce3+ ions are coupled to one another via their mutual hybridization with the bands. We have extended the Siemann–Cooper theory to the case of ions with more than one f electron (e.g., U3+, U4+, Pu3+). In our theory, the angular dependence of the two-ion interaction depends on the f occupation number and on the type of intraionic coupling. Here we provide a detailed exposition of the theory, and report on a new and important application to understanding the behavior of plutonium compounds.
Magnetic properties of CeSb1−xTex solid solution
Authors: Escorne M. , Mauger A. , Ravot D. , Achard J. C.
Published: February 2003

The variations of the crystal field splitting energy Δ=E(Γ8)−E(Γ7) has been studied as a function of the composition x for the solid solution CeSb1−xTex in the whole range 0<x<1. Independent determinations of Δ from magnetic susceptibility and resistivity measurements were made. A nonlinear variation of Δ with x is evidenced with a maximum value of Δ≂+70 K at x=0.035 and a crossing between Γ7 and Γ8 levels at x∼0.10. A minimum value Δ∼−180 K is found for x=0.5. This behavior can be understood if we suppose that not only holes in the valence band, but also electrons in the conduction band mediate an indirect exchange between Ce ions. We have studied the properties of the fourth-order indirect exchange Hamiltonian in the mixing parameter derived from the Anderson model. The resulting magnetic interaction includes the long-range Cooper exchange and antiferromagnetic short-range interactions. An overall qualitative agreement is found between theory and the experimental results.
Magnetic characteristics of RAgGa compounds
Authors: Sill L. R. , Esau E. D.
Published: February 2003

The bulk magnetic characteristics of the series of polycrystalline compounds RAgGa (where R is Pr, Nd, Gd, Tb, Dy, Ho, Er, or Tm) have been determined in applied fields up to 26 kOe and temperatures from 3 to 300 K. These compounds form with the body-centered orthorhombic crystal structure of the CeCu2 type. At high temperatures their reciprocal susceptibilities follow Curie–Weiss type behavior; their effective paramagnetic moments are in reasonable agreement with those calculated for the appropriate tripositive rare-earth ion; their asymptotic Curie temperatures are all relatively small and positive. At low temperatures, the Gd, Ho, and Er compounds order ferromagnetically; the Tb compound orders antiferromagnetically; the Dy compound is metamagnetic; the Pr and Tm compounds almost order ferromagnetically at the lowest measured temperature.
Orientation of Gd moments in RExGd1−xRh4B4 (RE=Ho, Er)
Authors: Noakes D. R. , Umarji A. M. , Shenoy G. K. , Hinks D. G.
Published: February 2003

The orientation of the Gd magnetic moment with respect to the crystallographic axes in the magnetically ordered states of GdRh4B4 and RExGd1−xRh4B4 (RE=Ho and Er) materials has been studied with the 155Gd Mössbauer effect. Rare-earth single-ion anisotropies induced by the crystalline electric field (CEF) force the Gd moment to point in particular directions. These directions depend on which rare earth has been substituted into the lattice and will be discussed in terms of a CEF model for these materials. The results demonstrate that the 155Gd Mössbauer effect can be used as a probe of magnetic ordering directions in rare-earth materials.
Evidence for spin-density-wave transition in dilute yttrium-gadolinium alloys
Authors: Wenger L. E. , Mydosh J. A.
Published: February 2003

In order to elucidate the possible existence of a spin-density-wave (SDW) transition in YGd, the heat capacity of five alloys with concentrations varying from 2 to 5 at. % Gd have been measured in the temperature range 1.5–30 K. Semicusp-like behavior is observed in the magnetic specific heats with the maxima occurring at similar temperatures as the susceptibility peaks. Additionally the magnetic entropy change between 0 K and the ordering temperature increases from 56% to 68% of cR ln(2J+1) for increasing concentrations. These calorimetric results suggest a long-range magnetic ordering and are in quantitatively good agreement to the mean-field predictions of the Overhauser thermodynamic treatment of antiferromagnetic ordering by a SDW mechanism.
Soliton dynamics in quantum Ising-like antiferromagnetic chains (invited)
Authors: Nagler S. E. , Buyers W. J. L. , Armstrong R. L. , Briat B.
Published: February 2003

The spin dynamics of quantum Ising-like antiferromagnetic chains is dominated by propagating domain walls or solitons. A characteristic low-frequency component of the dynamical spin correlation function associated with thermally excited solitons appears at elevated temperatures. The soliton effects on the correlation function can be observed in neutron scattering experiments on the quasi-one-dimensional magnetic materials CsCoBr3 and CsCoC3.
Hybridization-mediated anisotropic coupling and excitation behavior in cerium monopnictides
Authors: Cooper Bernard R. , Thayamballi P. , Yang D.
Published: February 2003

The neutron scattering measurements of Rossat-Mignod et al. on CeBi in the type I antiferromagnetic phase give unusual excitation behavior. The dispersion is anisotropic, being very flat for q∥k (the propagation vector of the structure), and showing a minimum at the zone boundary for q⊥k. Previously, the equilibrium behavior of CeBi has been explained using an interionic interaction arising from band-f electron hybridization (Coqblin–Schrieffer interaction) as mediated by the band electrons. The resulting interaction is very anisotropic, giving strong coupling within planes, with a much weaker coupling between planes transverse to a saturated moment. Using the same theory, we find that calculations of the excitation spectrum in the RPA at T=0 for a set of parameters giving equilibrium behavior similar to experiment, give results that compare well with the experimental excitation behavior of CeBi. The dispersionless behavior for q∥k and the minimum in energy at the zone boundary for q⊥k are both reproduced by our theory.
Dynamical correlation functions for one-dimensional quantum spin systems: New results based on a rigorous approach
Authors: Müller Gerhard , Shrock Robert E.
Published: February 2003

We present new results on the time-dependent correlation functions Ξn(t) =4〈Sξ0(t)Sξn〉, ξ=x,y at zero temperature of the one-dimensional S=1/2 isotropic XY model (h=γ=0) and of the transverse Ising model (TI) at the critical magnetic field (h=γ=1). Both models are characterized by special cases of the Hamiltonian H=−J∑l[(1+γ)SxlSxl+1 +(1−γ)SylSyl+1 +hSzl]. We have derived exact results on the long-time asymptotic expansions of the autocorrelation functions (ACF’s) Ξ0(t) and on the singularities of their frequency-dependent Fourier transforms Φξξ0(ω). We have also determined the latter functions by high-precision numerical calculations. The functions Φξξ0(ω), ξ=x,y have singularities at the infinite sequence of frequencies ω=mω0, m=0, 1, 2, 3, ... where ω0=J for the XY model and ω0=2J for the TI model. In both models the singularities in Φxx0 (ω) for m=0, 1 are divergent, whereas the nonanalyticities at higher frequencies become increasingly weaker. We point out that the nonanalyticities at ω≠0 are intrinsic features of the discrete quantum chain and have therefore not been found in the context of a continuum analysis.
The valence of cerium in metals (invited)
Authors: Wohlleben D. , Röhler J.
Published: February 2003

The valence of Ce in solids can be measured by LIII x-ray absorption. One finds γ- and α-like materials with Ce valences clustering near v≳3 and near v≊3.25, respectively. There are no Ce metals with valence four. The valence of Ce is determined by a competition between the elastic strain energy of the mixture of three and four valent Ce atoms and the free energy due to configurational mixing. The latter has a minimum near valence 3.25, which decreases strongly with decreasing volume and eventually traps the valence of all α-like materials near its bottom.
M-edge x-ray absorption spectroscopy of 4f instabilities in rare-earth systems (invited)
Authors: Kaindl G. , Kalkowski G. , Brewer W. D. , Perscheid B. , Holtzberg F.
Published: February 2003

Soft x-ray absorption spectroscopy in the M-edge region is explored as a tool for studying 4f instabilities. The quasiatomic MIV,V spectra, recorded by total-electron yield under UHV conditions, carry information on the initial-state 4f occupancy. For compounds of the heavy rare earths, even at high dilution (e.g., Tm0.05Y0.95Se), mean valences can be derived, which agree with those from lattice-constant systematics (e.g., for TmSe and Sm0.3Y0.7S). A moderate surface sensitivity allows the observation of surface-induced valence changes on EuPd3, TmS, and SmAl2. The MIV,V spectra studied for 10 Ce compounds fall in two categories: pure 3d94f1 final-state multiplets for γ-like compounds, and additional peaks at about 5 eV higher energies for α-like and intermediate systems. With increasing intensity of the satellites, which are assigned to 3d94f1 final states, the 3d94f2 multiplet structure gets washed out. An interpretation of the spectra with the recent Anderson-impurity theory of Gunnarsson and Schönhammer leads to 4f occupancies greater than 0.7, even in extreme α-like systems. In addition, MIII-edge spectra exhibit one peak in γ-like and two peaks in α-like and intermediate Ce systems, which are assigned to 3p54f1 and 3p54f0 final corestates. With increasing α-like character, the 4f1 peak is found to move to higher energies presumably due to a decrease in 4f screening with increasing 4f hybridization.
Bound state of phonons and a crystal field excitation in CeAl2 (invited)
Authors: Thalmeier P.
Published: February 2003

In rare earth compounds the coupling of lattice vibrations to the crystalline electric field (CEF) states of 4f-electrons plays an important role. It is shown that under suitable conditions this magnetoelastic interaction can lead to a ‘‘bound state’’ between CEF excitations and lattice vibrations. The existence of this bound state in the intermetallic Laves phase CeAl2 explains the results of inelastic neutron scattering experiments which have not been understood before. The properties of these bound states and their consequences for thermodynamic quantities are discussed. In addition the phonon softening at low temperatures found in CeAl2 is discussed.
Exchange interaction between ferromagnetic domain wall and electric current in very thin metallic films
Authors: Berger L.
Published: February 2003

Since the wall thickness is at least 102 electron wavelengths, a domain wall acts, through the s-d exchange interaction, like a very weak and smooth potential barrier of height ≂10−2 eV, which does not reflect conduction electrons appreciably. The potential energy arises from the 4s conduction electron spin making a small angle with the local s-d exchange field. Anisotropic s-d exchange may also contribute to the potential barrier. A solution of the electron transport equations in the wall is obtained. In order for an electron current crossing the wall to exert an appreciable drive force on it, nonzero interband electron scattering by impurities or phonons is needed. The electron density for a given band varies slightly with location inside the wall, and depends on the current. Mutual electrostatic shielding between bands is taken into account. The drive force per unit wall area is F≂2Ms  μ−1i (ve −vw), where ve and vw are electron drift speed and wall speed. In other words, this drive force at ve ≠0 is governed by the same intrinsic wall mobility μi as the well-known intrinsic wall damping force at vw ≠0. While hydromagnetic ‘‘domain drag’’ forces associated with the Hall effect are dominant in samples of usual thickness, this ‘‘exchange domain drag’’ force is expected to dominate in films thinner than ≂0.1 μm.
L
III absorption, resistivity, and susceptibility studies of the Ce(Ni1−xCox)2 and Y(Ni1−xCox)2 systems
Authors: Scoboria P. , Harrus A. , Andraka B. , Mihalisin T. , Raaen S. , Parks R. D.
Published: February 2003

We have measured the valence of Ce in Ce(Ni1−xCox)2 by LIII absorption and find that it is constant at 3.20±0.02. However, striking variations in the resistive behavior are seen across this series. Even more pronounced variation in resistive behavior, as well as, large changes in the susceptibility are seen in the Y(Ni1−xCox)2 system. It is argued that d electron spin fluctuations may be responsible for the observed behavior in both systems.
Surface and bulk valence of Y0.9Yb0.1Al2 and La0.9Yb0.1Al2
Authors: Penney T. , Reihl B. , Pollak R. A. , Barbara B. , Plaskett T. S.
Published: February 2003

Photoemission and susceptibility measurements have been made on alloys of 10% YbAl2 with 90% YAl2 or LaAl2. Similar to YbAl2, Yb in the YAl2 host is intermediate valent in the bulk consistent with a single ion picture. Yb in the LaAl2 host has a valence of 2.0–2.1 in the bulk. In both cases the surface is completely divalent and the surface 4f emission is shifted to higher binding energies relative to the bulk 4f emission.
Magnetic ordering, Kondo lattice, and mixed valence behavior in the Ce1−xYxIn3 system
Authors: Teter J. , Crow J. E. , Mihalisin T.
Published: February 2003

The Néel temperatures of Ce1−xYxIn3 samples are determined by both susceptibility and resistivity. The substitution of Y for Ce drives TN to zero at x∼0.4, due to increased Kondo scattering. For x>0.6 both susceptibility and resistivity suggest that the Ce ions are mixed valent.
Transport properties of Mn2−xCrxSb near antiferro-ferrimagnetic transition point
Authors: Sato K. , Nakazima M. , Miyazaki T. , Isikawa Y. , Mori K.
Published: February 2003

Compounds Mn2−xCrxSb show a first-order transition from ferrimagnetic to antiferromagnetic states with decreasing temperature, which is called the exchange inversion. Here, the temperature and magnetic field dependences of the thermal conductivity and electrical resistivity near the exchange inversion temperature Ts for Mn1.88Cr0.12Sb were measured. The thermal conductivity near the transition temperature Ts increased 11% in an applied field H=15 kOe at 297.5 K. The exchange inversion entropy ΔS for zero field and 15 kOe were estimated as 1.4 and 2.0 J/mol K, respectively.
Neutron diffraction study of hard magnetic alloy MnAlC
Authors: Yang Ying-chang , Ho Wen-wang , Lin Chin , Yang Ji-lian , Zhou Hui-ming , Zhu Jia-xuan , Zeng Xiang-xin , Zhang Bai-shen , Jin Lan
Published: February 2003

The crystal and magnetic structure of the hard magnetic alloy Mn1.074Al0.871C0.005, which has a body centered tetragonal structure, has been investigated. Neutron diffraction data shows that Mn0.992, C0.008 occupy the (0,0,0) site and Mn0.082, Al0.871, C0.047 occupy the ( 1/2 , 1/2 , 1/2 ) site. The magnetic moments of manganese atoms are along the c axis, pointing in opposite directions for the two sites. Comparing these results with those of Mn1.09Al0.91, the significant improvement of magnetic and mechanical properties in the ternary alloy MnAlC is explained.
Pr-Fe and Nd-Fe-based materials: A new class of high-performance permanent magnets (invited)
Authors: Croat J. J. , Herbst J. F. , Lee R. W. , Pinkerton F. E.
Published: February 2003

We report the properties of a new class of high-performance permanent magnets prepared from Nd-Fe-B and Pr-Fe-B alloys. Magnetic hardening is achieved by rapid solidification. Energy products of these isotropic materials can exceed 14 MGOe with intrinsic coercivities of ∼15 kOe. X-ray and microstructural analyses indicate that the alloys exhibiting optimum characteristics are comprised of roughly spherical crystallites, strongly suggesting that the coercivity mechanism is of the single-domain particle type. The crystallites are composed of an equilibrium R-Fe-B intermetallic phase having tetragonal symmetry, and the stability of this phase with respect to other rare earths and other metalloids has been investigated.
Magnetic hardening in rapidly quenched Fe-Pr and Fe-Nd alloys
Authors: Sellmyer D. J. , Ahmed A. , Muench G. , Hadjipanayis G.
Published: February 2003

We report studies of high-field magnetization and thermomagnetic effects in rapidly quenched and heat treated alloys based on Fe-Pr and Fe-Nd. Coercivities up to ∼40 kOe and large energy products result from the precipitation of a finely dispersed crystalline phase. Studies of varying the alloy composition and heat treatment are reported.
Stress and induction dependence of hysteresis losses in electrical steels
Authors: Foster K.
Published: February 2003

Hysteresis losses Ph were measured for several electrical steels over an induction range of 0.4–1.7 T as a function of stress coatings and applied tensile stress. The Bn dependence of Ph was determined, where n is the Steinmetz coefficient. Removal of stress coatings from high permeability oriented (HGO) steel samples decreased n from about 2 to 1.6, while application of stress coatings to uncoated regular grain oriented samples increased n from 1.6 to 1.9–2. An applied tensile stress of about 7 MPa increased n from about 1.6 to 2 for both RGO and HGO samples. A similar tensile stress level increased n from 1.6 to about 1.8 for a nonoriented silicon steel sample.
Preparation of homogeneous Mn-X-Bi (X=Cu, Ni) thin films by rf sputtering
Authors: Gomi Manabu , Kajima Makoto , Abe Masanori
Published: February 2003

The conditions (annealing temperature and chemical composition) for preparing Mn-X-Bi (X=Cu, Ni) thin films with good homogeneity have been investigated. The films were made by annealing two-layered films of Mn-Cu (or Mn-Ni) and Bi deposited by rf sputtering. The annealing temperature to crystallize the Mn-Cu-Bi(Mn-Ni-Bi) films was above 245 °C (∼195 °C). The optimum compositions for getting good homogeneity of the film were nominally determined as Mn6Cu4Bi4 and Mn5Ni2Bi4. At these compositions, the magneto-optic activity and coercive force of the film became highest: For Mn6Cu4Bi4(Mn5Ni2Bi4) film with a thickness of 60 nm (80 nm), Faraday rotation was about 1.3° (∼1.1°) at λ=633 nm and the coercive force was 1.9 kOe (0.2 kOe). It has been found that the inhomogeneity of the film is suppressed by adding Te.
Surface layer contraction of the lattice in YIG:Ca films
Authors: Antonini B. , Brandle C. D. , Lagomarsino S. , Paoletti A. , Paroli P. , Tucciarone A.
Published: February 2003

YIG:Ca films (Ca=0.23 afu) are subjected to extended annealing treatments in H2 atmosphere at increasing temperatures and the effects on the structure are investigated by double-crystal x-ray diffraction and magneto-optical measurements. Initially, an elastic expansion of the lattice constant a⊥ from 12.3755 to 12.3798 Å is observed in the direction orthogonal to the film surface, which operates uniformly over the film bulk, while the Fe4+ population goes to zero as a result of the Fe4+→Fe3+ reduction. After completion of the Fe4+ reduction, an inward collapse of the lattice occurs, of about 0.02 Å, starting from the surface and extending to thicker layers as the reduction cycle continues. The x-ray diffraction profiles exhibit Pendellösung interference and the thin surface layer is further studied by a successive-etching experiment. This layer is found to form epitaxially over the film bulk, thus producing a lateral stress, and presents a strain profile at the layer-bulk interface. Intense near-infrared magnetic circular dichroism is observed, which results from Fe3+→Fe2+ reduction. The surface layer formation is totally reversible by annealing in O2.
A novel method for measuring magneto-optical figures of merit: Light scattering (abstract)
Authors: Zhang P. X. , Tu An , Liu Y. L.
Published: February 2003

By analyzing the influence of Faraday rotation and light absorption on the scattering processes, it is found that the change of scattering intensity of certain modes depends directly upon the figure of merit Q (Q=θF/2α, where, θF is the Faraday rotation angle and α is the coefficient of absorption) of the materials concerned. Thus in an experiment of Raman scattering from magnetic materials, applying a longitudinal magnetic field (H∥K, where K is the direction of light propagation, that is the Faraday arrangement) and a transverse magnetic field (H⊥K), two scattering cross sections Is and I′s will be obtained, which correspond to the processes with and without the influence of Faraday rotation. The ratio Is/Is is uniquely related to the merit of figure Q. Taking Raman active phonon of iron garnet (O10h space group) as example, we quantitatively evaluated the dependence of I′s/Is on Q.
Nonlinear boundary element method for two-dimensional magnetostatics
Authors: Lean Meng H. , Bloomberg Dan S.
Published: February 2003

An interface formulation, successfully used for the solution of magnetostatic fields in piecewise homogeneous media, is extended to nonlinear media problems. The advantage of boundary integral techniques, in the reduction of problem dimensionality, is retained. This nonlinear boundary element method (BEM) algorithm alternates solution of the augmented interface equation with satisfaction of the constitutive media relations. Use of the M̄-B̄ chararteristics is shown to guarantee iteration stability because the slope approaches unity as μ tends to infinity. Isoparametric elements of second order are used for both geometry and sources to ensure high solution fidelity. Galerkin’s method is employed for discretization to matrix form. Each iteration requires only the product of the inverted system matrix with the augmented RHS. Examples include saturation of square and circular cylinders of high permeability in a uniform field. It is shown that with an optimal relaxation factor of 0.65, only 3–6 iterations are needed for convergence to 3% error tolerance in both magnetization and surface currents.
Sharp transitions in perpendicular recording
Authors: Beardsley I. A. , Tsang C.
Published: February 2003

A simple continuum model and a discrete model are proposed in order to examine the issue of the existence of sharp transitions in perpendicular recording. Both approaches, even though fundamentally different, give a range of material parameters where transition sharpness is limited only by exchange. In the discrete model the head field gradient determines the sharpness of an isolated transition. However, when a periodic pattern is considered the optimization of the head depends critically on the density and magnetization regime.
Effects of a sublayer on readback from a vertical film
Authors: Baker Bill
Published: February 2003

Analytical and numerical boundary integral methods are used to compute the pulse and frequency response of asymmetric thin-film heads and double layer vertical recording films. Nonclassical thickness factors arise. An approximate analytic solution illustrates the implicit dependence upon spacing between head and sublayer. Experimental results agree closely with calculations.
Effect of uniaxial tensile stress on the permeability of monocrystalline MnZnFeII ferrite
Authors: Visser E. G.
Published: February 2003

After application of a uniaxial stress to a frame of monocrystalline MnZn ferrite, the stress dependence of the permeability was measured. In addition the disaccommodation was measured and analyzed in detail. All results were satisfactorily explained by means of a simplified theoretical model. A high imaginary component of the permeability at frequencies of up to 3 MHz was found to be caused by the domain walls. It appears that the application of a well-defined stress provides a means of controlling the permeability of the ferrite.
Heat-treatment effect on microstructure and magnetic properties of sputtered CoCr films
Authors: Fujii Y. , Tsutsumi K. , Numata T. , Sakurai Y.
Published: February 2003

Heat-treatment effects on the saturation magnetization Ms, the coercivity Hc, and the perpendicular anisotropy Ku of CoCr films with rather low Hc were investigated. Heat treatment up to 450 °C caused interdiffusion of Co and Cr atoms in a compositionally modulated film, resulting in reduction of Ms. On the other hand, heat treatment at 500 °C increased Ms, Hc, and Ku, which was interpreted to be the segregation of nonmagnetic alloy. Measurement of the temperature dependence of Ms supported this interpretation. Heat treatment at 500 °C seemed to have the similar effect on microstructure in a film to substrate heating during deposition. From Ku-Ms curves, the packing density of the ferromagnetic region in heat-treated films was estimated to be 77% of that in as-sputtered ones.
Os-doped γ-Fe2O3 thin films having high coercivity and high coercive squareness
Authors: Ishii O. , Hatakeyama I.
Published: February 2003

Sputtered γ-Fe2O3 thin films are attractive for use in high density magnetic recording disk media. This paper reports on remarkable improvements made in magnetic properties for γ-Fe2O3 thin films and their microstructures. We have found that high coercivity and high coercive squareness can be obtained by doping γ-Fe2O3 with a small amount of Os. Os-doped γ-Fe2O3 films 0.1–0.2 μm thick have been prepared on anodized Al alloy substrates by reactive sputtering of an Fe-Os target, and successive reduction and oxidization treatments. The coercivity and coercive squareness of the film increase with Os content. A γ-(Fe0.948Os0.052)2O3 film exhibits the maximum coercivity of 2100 Oe and high coercive squareness of 0.81. Furthermore, Os doping to the γ-Fe2O3 film brings about field-induced anisotropy (∼105 erg/cc), resulting from the annealing at 250 °C for 1 h in a magnetic field (7 kOe). This induced anisotropy greatly increases the coercive squareness parallel to the easy axis. A coercive squareness of 0.96 is obtained for the γ-(Fe0.948Os0.052)2O3 film after the magnetic annealing. Fine crystallites of about 400 Å in diameter are obtained by Os doping which suppresses grain growth during preparation heat treatments.
Spin-echo NMR study of the atomic environment in the Fe100−xBx metallic glass system
Authors: Ford J. C. , Budnick J. I. , Hines W. A. , Hasegawa R.
Published: February 2003

In order to investigate the near-neighbor atomic environments, we have measured the 11B spin-echo NMR spectra for the melt-spun Fe100−xBx metallic glass system (14≤x≤22) at 4.2 K over the frequency range 22–46 MHz. The addition of B to Fe100−xBx shifts the peak in the hyperfine field distribution to smaller values by adding intensity to the low field portion of the distribution while leaving the high field portion unchanged. These results, along with 57Fe hyperfine field measurements from Mössbauer experiments are being used to establish a model relating hyperfine fields and structural changes.
Mössbauer spectroscopy and scanning electron microscopy study of iron-graphimet
Authors: Lin M. C. , Barnes R. G.
Published: February 2003

5 7Fe Mössbauer effect spectroscopy (ME), electron spin resonance (ESR), and computer-controlled scanning electron microscopy (CCSEM) have been used to investigate samples of commercial iron-graphimet (reduced iron-chloride intercalated graphite), which is of interest because of its role in the methanization of carbon. The CCSEM results indicate that most of the inorganic particles ranging in size between 0.2 and 40 μm are mixtures of iron chlorides giving average x-ray fluorescence spectra of Fe and Cl in the approximate ratio 1 : 2. At 300 K the ME spectrum consists of three broad lines of unequal intensity plus the usual six-line pattern of metallic iron. A complex pattern gradually develops out of two of the broad lines with decreasing temperature below 77 K. From the hyperfine field obtained at 13 K and the ESR spectrum, this phase has been identified as ultrafine nonstoichiometric iron oxide, magnetite (Fe3O4). The broad, asymmetric quadrupole doublet in the 13-K spectrum has the isomer shift and quadrupole splitting typical of high-spin Fe2+. These values are close to those of anhydrous FeCl2 and FeCl2-intercalated graphite. During measurements at 800 K in vacuum (∼10−5 Torr), the oxide particles partially agglomerate through sintering, and the normal ME spectrum of Fe3O4 is observed.
Interacting phase transitions in Fe1+xCr2−xO4 (0≤x≤0.4)
Authors: Kose K. , Iida S.
Published: February 2003

The system Fe1+xCr2−xO4(0≤x≤0.4), in which a cooperative Jahn–Teller transition and a magnetic transition take place in the same temperature range, has been investigated by x-ray, magnetization, Mössbauer effect, and specific heat measurements. When 0.00≤x≤0.25, the Jahn–Teller transition temperature TD is higher than that of the magnetic transition TN, two peaks being observed in the specific heat. When x increases TD decreases slightly, whereas TN increases steeply, so that they coincide at x=0.275 with TD=TN=130 K, exhibiting a very sharp lambda type heat anomaly. When x>0.30, TD is expected to be lower than TN, but no distinct heat anomaly was observed in the expected temperature range. This indicates that the two cooperative phase transitions can couple when the higher temperature transition introduces a crucial part of the entropy lowering which would be expected after the lower temperature transition.
Anomalous changes in the dielectric constants of MnF2 near its Néel temperature
Authors: Seehra Mohindar S. , Helmick R. E.
Published: February 2003

The first observations of anomalous changes in the dielectric constants (ε) of the uniaxial antiferromagnet MnF2 near its TN≂67.3 K are reported. Measurements of ε∥(E∥c) and ε⊥(E⊥c) were carried out from 4.2 to 300 K at rf (10 kHz) using a three-terminal capacitive method. Beginning with 300 K where ε∥=7.645 and ε⊥=8.910, both ε∥ and ε⊥ decrease with decreasing T. The lattice contribution is determined from the fit to the equation ε(T)=ε(0)+A/[exp(T*/T)−1], with the constants ε∥(0)=7.3253, A(∥)=1.0487, T*(∥)=420 K and ε⊥(0)=8.4954, A(⊥)=0.7694, and T*(⊥)=314.7 K in the 100–300 K range. For T<100 K, magnetic contributions to ε viz. εm are observed, εm∥ being positive and εm⊥ negative. At 4.2 K εm⊥=−0.13 and εm∥=0.025. Below TN, ‖εm∥‖ and εm⊥ are found to vary as σ2 (σ=sublattice magnetization) whereas above TN, ‖∂εm⊥/∂T‖ yields specific-heat type singularity. Exchange-striction mechanism is invoked to yield εm∝ spin pair-correlation function, which in the mean-field approximation can explain the observed temperature variations. However the opposite signs of εm∥ and εm⊥ and their different magnitudes are not yet understood.
Magnetism of hydrated rare-earth bromates
Authors: Simizu Satoru , Bellesis G. H. , Friedberg S. A.
Published: February 2003

The dc magnetic susceptibility has been measured for several rare-earth bromates, R(BrO3)39H2O, RBR, (R=Pr, Tb, Dy, Er, Tm), using a SQUID magnetometer between ∼0.06 and 4 K. The hexagonal structure of RBR crystals is similar to that of the rare-earth ethylsulfates, RES. Ferromagnetic transitions were observed at 0.125 K for TbBR and 0.170 K for DyBR. For other RBR no ordering was detected to the lowest temperature attained. The magnetic properties observed for all RBR studied here are very similar to those of corresponding RES but show subtle and interesting differences reflecting small differences in the crystal fields. As in the RES, short-range exchange interaction in the RBR appears to be negligible compared with dipolar interaction.
Magnetic properties of four Cu(i
i)-amino acid salts
Authors: Calvo Rafael
Published: February 2003

We report a comparative study of magnetic properties of the Cu(II) salts of the amino acids l-alanine, dl-α-amino-n-butyric acid, α-amino isobutyric acid, and l-isoleucine. The position of the EPR lines of these quasi-two-dimensional magnetic systems was measured as a function of temperature T between 293 and 1.5 K, at 9.3 GHz and for magnetic fields applied along three axes of single crystal samples. Large changes of the gyromagnetic factor with T have been observed. They are attributed to an internal mean field, proportional to the applied field, which appears when the temperature is lowered due to short range magnetic order in the paramagnetic phase of the salts. The problem of short range magnetic order and g shifts in Cu-amino acid salts is discussed and compared with previous observations in Mn one-dimensional systems.
Antiferromagnetic salts of [Gd(C5H5NO)8]3+ (abstract)
Authors: Carlin Richard L. , Burriel R. , Mennenga G. , de Jongh L. J.
Published: February 2003

The first studies at low temperatures on pyridine N-oxide complexes of the rare earths are reported. Susceptibility and specific heat measurements show that both [Gd(C5H5NO)8](ClO4)3 and [Gd(C5H5NO)8]I3 order antiferromagnetically at 70 mK. The perchlorate salt exhibits in the specific heat the high temperature T −2 behavior anticipated for dipole-dipole interaction.
Experimental studies of random-field effects in uniaxial random antiferromagnets (invited)
Authors: Wong Po-zen , Cable J. W. , Dimon P.
Published: February 2003

We discuss how random fields (RFs) are generated in uniaxial random antiferromagnets (URAFs) by applied fields and review the experiments that have been performed on these systems. They include direct and indirect specific heat measurements, neutron-scattering experiments, and phase diagram studies. We compare the results of different experiments on different systems, discuss their implications on the theories, and suggest further experiments. A new explanation for the Lorentzian-squared (LSQ) structure factor observed in the neutron-scattering experiments is also given.
Position-space rescaling and hierarchical lattice models of disordered one-dimensional systems (invited)
Authors: Tremblay A.-M. S. , Breton P.
Published: February 2003

The application of exact and approximate position-space renormalization group techniques to the calculation of densities of states for problems with Gaussian generating functions (such as free tight-binding electrons, harmonic vibrations, spin waves, or random walks on Euclidian or ‘‘fractal’’ lattices) is briefly reviewed. It is also shown that for one-dimensional Gaussian theories with disorder, the approximate recursion relations proposed by Gonçalves da Silva and Koiller (GK) are exact for problems formulated on Berker–Ostlund lattices. A generalization of the GK scheme which allows one to calculate the optical zone-center density of states is formulated and then applied to the study of one- and two-mode behavior in mixed diatomic crystals.
Capacitance measurement of magnetic specific heat
Authors: King A. R. , Belanger D. P. , Nordblad P. , Jaccarino V.
Published: February 2003

A new technique–low frequency capacitance (C) measurement–has been used to study the critical behavior of both isotropic and anisotropic antiferromagnets. We find that dC/dT is accurately proportional to the known magnetic specific heat Cm of FeF2. This indicates that both dε/dT and dl/dT scale with Cm. For cubic KNiF3, the critical exponent (Cm=At−α) has been found to be α=−0.151±.004 and A/A′=1.56±0.03. The experiments measured the capacitance of disk-shaped samples with a three-terminal capacitance technique. A ratio transformer bridge was employed, yielding a resolution in ΔC/C of about 10−8. The quality of the results is comparable to the best obtainable from conventional Cm and birefringence measurements.
Orderings and renormalization-group flows of a stacked frustrated triangular system in three dimensions
Authors: Nihat Berker A. , Grest Gary S. , Soukoulis C. M. , Blankschtein Daniel , Ma M.
Published: February 2003

Two distinct partially ordered phases have been revealed by the Landau–Ginzburg–Wilson and Monte Carlo studies of the stacked frustrated triangular Ising model. These two types of order, occurring consecutively as temperature is lowered, and an observed shifting between equivalent ordered phases at a given temperature can be explained by a physical interpretation of the expected global renormalization-group flows in temperature and sixfold symmetry-breaking field acting on the two-component order parameter. New Monte Carlo data are presented, which confirm long-range order and a previous prediction of the above interpretation. The transition from the paramagnetic phase is in the XY universality class, whereas the transition between the ordered phases appears to be a sixfold symmetry-breaking flop.
Potts models and the critical behavior of a cubic ferromagnet with fourth and sixth-order anisotropy
Authors: Cullen James , Callen Earl
Published: February 2003

The critical behavior of the magnetization of a cubic ferromagnet in a magnetic field is analyzed for all field directions when both fourth and sixth-order anisotropy are present. Results are presented for K1>0 and all κ(K2/K1). For −6<κ<9 the phase diagram is of the three-state Potts type. For κ>9 a 60° rotation of the three-state diagram is obtained at high fields and a reentrant feature at lower fields. For κ=9 a special critical point appears on the [111] axis. The connection between this result and an extended version of the Landau theory is made. Finally, the κ≤−6 ([110] hard) diagram is displayed and the nature of the critical points, lines, and surfaces discussed.
Phase transitions in the six-state vector Potts model in two dimensions
Authors: Murty Challa S. S. , Landau D. P.
Published: February 2003

The static critical properties of the six-state vector Potts model (clock model) on L×L square lattices are studied in zero field using Monte Carlo simulations. Data are obtained for L≤48 keeping between 2.4 and 4.0×104 MCS (Monte Carlo steps/site) for computing averages. The data are analyzed using a block distribution technique in which the critical temperature and exponents may be estimated from the size dependence of the cumulants of the order parameter. We see clear evidence for two phase transitions but our estimates for the transition temperatures are different from results obtained through other methods. For the lattice sizes considered the intermediate phase does not appear to be XY-like.
Magnetic order of FeCl3 and CoCl2 intercalated graphite
Authors: Simon Ch. , Batallan F. , Rosenman I. , Schweitzer J. , Lauter H. , Vangelisti R.
Published: February 2003

We have investigated by neutron diffraction the magnetic properties of first- and second-stage FeCl3 and CoCl2 graphite intercalation compounds. They can be considered as quasi-two-dimensional magnetic systems in which one can vary both the 3D magnetic coupling and the intralayer magnetic interactions. The FeCl3 compounds are Heisenberg systems in which we have found that strong 2D magnetic correlations develop below 40 K; in the first-stage compound, the 3D coupling is strong enough to allow a transition to a 3D order below 3.8 K. The in-plane order is always an incommensurate modulation. In the CoCl2 compounds we have observed on the contrary an antiferromagnetism along c axis with the moments in the layer plane. They are 2D X-Y systems with a Kosterlitz–Thouless transition in which however the 3D coupling plays an important role.
Computer simulation of a 1d quantum ground state
Authors: Novotny M. A. , Landau D. P.
Published: February 2003

The development of a Monte Carlo renormalization group (MCRG) method to study quantum systems is reported. This method can be used either to study the ground state of the system or to study the system at a finite temperature. In this paper we illustrate the MCRG method by applying it to the ground state of the one-dimensional Ising model in a transverse magnetic field. Very rapid convergence to the known critical exponents is found even for small lattice sizes.
Microwave properties of GdFe2:H3 films
Authors: Vittoria C. , Schelleng J. H. , Lubitz P. , Forester D. W.
Published: February 2003

Ferromagnetic resonance (FMR) fields and linewidths of amorphous GdFe2:H3 films have been measured for temperatures from 6 to 500 K at x band. A special procedure was devised in order to introduce and maintain hydrogen gas in films of GdFe2. Magnetometer measurements were performed on the same films. We find that for GdFe2:H3 the magnetization goes through a compensation point near T=300 K and the Neel temperature is 450 compared to 500 K for unhydrided GdFe2. The g factor obeys the Wangsness relation as a function of temperature. The FMR linewidth ΔH is proportional to 1/M except for 20<T<90 K where ΔH exhibits a maximum for T=40 K.
Magnetostriction in amorphous FeNiCrMoBSi ribbons
Authors: du Tremolet de Lacheisserie E. , Krishnan R.
Published: February 2003

We have measured the thermal expansion, the spontaneous magnetostriction λS, and the forced volume magnetostriction ∂ω/∂H in amorphous Fe40−x/2Ni40−x/2CrxMo2B8Si10 (0<x<5) alloys using an improved capacitance technique: the ribbons are wound into cylinders and slipped into copper rings. The experimental method presented here is interesting because it covers a large temperature range: 4.2 –1000 K. We have observed the Curie temperature TC indicated by a marked peak in the thermal variations of ∂ω/∂H and the recrystallization temperature Tx by an isothermal contraction of the sample. The thermal variations of the spontaneous magnetostriction have been analyzed in the framework of the one-ion model which accounts also for the dependence of λS on the Cr content.
Electromagnetic generation of 9.4-GHz phonons in Fe and Ni
Authors: Alexandrakis G. C. , Dewar G.
Published: February 2003

The conversion of microwaves to phonons has been observed and studied in thick iron and nickel single crystal and polycrystalline films. The experiments were of the transmission type with the sample forming part of the common wall between two microwave cavities. Sound is generated in the presence of a static magnetic field by the Lorentz force, causing the electronic current to drive the lattice. The sound amplitude, which is enhanced in certain field configurations by the sample’s magnetization, is essentially field independent after saturation for applied fields of the order of 10 kOe and increases as the temperature decreases from room temperature to 77 K. These results explain previously misinterpreted observations in iron, nickel, and other ferromagnetic metals. High frequency constant amplitude sound could be used as a tool to study the electronic properties of ferromagnetic metals.