bluuebunny/crossref_metadata_2025 huggingface dataset:
Remanence in spin glasses : A new approach from zero field NMR in CuMn
Authors: Alloul H.
Published: February 2003

Zero field Cu NMR of the first and fourth nearest neighbours of Mn in spin glass CuMn (concentrations from 0.4% to 4.7%) have been detected for T<Tg/5. The enhancement factor η of the rf field and NMR signal intensity, associated with the rotation of domain magnetization, has been found roughly proportional to the remanent magnetization σ and is negligible when the sample has been zero field cooled. These results contradict the independent domain model for which η should be independent of σ. The data reveal the existence of a well defined anisotropy field HA induced (as σ) by the cooling field Hc, the anisotropy energy being roughly a constant. Transverse susceptibility and NMR intensity analyses confirm that most Mn spins are involved in the collective response to a transverse field and that HA is defined on a macroscopic scale. Direct observation by NMR of the shifted hysteresis loops and comparison with magnetization data imply that HA includes both an uniaxial Hax) and an unidirectional (Hd) anisotropy field, and that the magnetization reversals, when detected, occur for fields ‖Ho+Hd‖<Hax. The simultaneous occurrence of collective and irreversible phenomena in spin glasses is discussed.
Experimental verification of the theory of critical resistivity
Authors: Balberg I.
Published: February 2003

In recent years detailed predictions were made concerning the temperature dependence of the critical resistivity. It is shown here that experimental results obtained for a ferromagnetic metal (Fe), a ferromagnetic semi-conductor (p-type CdCr2Se4), an antiferromagnetic semiconductor (MnTe) and an antiferromagnetic metal (Dy) confirm the theoretical predictions quantitatively. The quantitative comparison of the theory and the experimental results yielded the specific heat parameters, α=α′=−0.21, A/A′=1.48 for Fe, α=α′=−0.01, A/A′=1.37 for MnTe and α=α′=−0.04, A/A′=1.44 for Dy. These results are in reasonable agreement with results from specific heat measurements and with results obtained in renormalization-group calculations.
Magnetic interactions and short range order in gadolinium gallium garnet
Authors: Kinney W. I. , Wolf W. P.
Published: February 2003

Previous studies of gadolinium gallium garnet (GGG) have indicated relatively strong antiferromagnetic interactions but, somewhat surprisingly, no evidence of long range magnetic order at temperatures down to 0.35 K. To understand this behavior, we have measured the non-dipolar interactions between first, second and third nearest neighbors, using an improved high frequency relaxation method, and we have combined the results in a Monte Carlo computer simulation to calculate the thermal properties. General agreement with the earlier specific heat measurements is obtained and it is concluded that the broad peak observed near 0.8 K is due to short range order resulting from ’’frustration’’ caused by the unusual structure of the garnet lattice.
Hyperfine magnetic field measurement in Heusler alloys with rhodium-99 and indium-111 by TDPAC technique
Authors: Jha S. , Saleh Naser , Julian Glenn M. , Ward T. E. , Blue James W. , Liu David C.
Published: February 2003

The hyperfine magnetic field (hmf) at nonmagnetic impurities Ru and Cd in Heusler alloys Rh2MnGe and Rh2MnSn has been measured as a function of temperature by the Time Differential Perturbed Angular Correlation (TDPAC) technique. Measurement of the hmf at the Ru utilized the 20.7-nsec 90 keV state in 99Ru populated in the decay of 16-d 99Rh; alloys were prepared using Rh metal powder bombarded with ?60 MeV protons. Measurement of hmf at Cd in Rh2MnSn utilized the 84-nsec 247 keV state in 111Cd populated in the decay of 2.8-d 111In; the alloy was prepared by substituting for 2 atomic per cent of Sn with In metal bombarded with 37 MeV protons. The measured hmf’s in kG at Ru impurity at Rh site are (with temperatures in parentheses) in Rh2MnGe: 195±11 (77 K), 126±4 (293 K), and 49±4 (355 K); in Rh2MnSn: 137±2 (293 K) and 37±6 (355 K). The measured hmf’s at Cd impurity (presumably at Sn site) in Rh2MnSn are 189±5 (77 K), 113±5 (293 K), and 33±3 (373 K).
Magnetic domain structures in multilayered NiFe films
Authors: Herd S. R. , Ahn K. Y.
Published: February 2003

The coercivity of NiFe (80/20) films can be lowered by laminating several layers with nonmagnetic spacers. A reduction by a factor of 10 can be achieved with a simple bi-layer, regardless of spacer material, provided the spacer thickness is below a critical value. No further reduction is found for multilayers. Two peaks of Hc near thicknesses of 250Å and 1000Å for single layer films, associated with changes in domain structure, are suppressed by lamination. After a minimum spacer thickness (S) of 10–15Å, the domain walls in the separate layers no longer coincide but track closely, their separation depending on S. With S?100Å the layers switch independently, giving rise to multiple values of Hc.
Enhancement of magnetic separability in coal liquefaction residual solids
Authors: Jacobs I. S. , Levinson Lionel M.
Published: February 2003

The conversion of coal to a clean fuel through liquefaction requires the physical separation of undissolved sulfur-rich mineral matter. The hydrogenation-liquefaction reaction produces residual solids in which the original coal impurity pyrite, FeS2, has largely been converted to pyrrhotite, Fe1−xS, which is a complex non-stoichiometric sulfide. Using thermomagnetic analysis and Mössbauer spectroscopy we show that the iron sulfide in coal liquefaction residues corresponds to an intermediate pyrrhotite. Striking transformations between various magnetic and non-magnetic states are induced by thermal treatments in inert or sulfidation atmospheres. The kinetics of the transformations are strongly influenced by prior thermal and atmosphere history. Transformation to a high magnetization state has practical application wherein magnetic separation techniques become attractive for the liquid-solids separation step in coal liquefaction.
Lodestone-explanation for magnetic properties and characterization of the source of magnetic hardening
Authors: Wasilewski P. J.
Published: February 2003

A Class I lodestone is a massive iron ore which owes its magnetic hardness to oxidation. Oxidation of the Fe3O4 results in a fine intergrowth of γ Fe2O3 in host Fe3O4, a requisite for all lodestones studied. The natural remanence (NRM) to saturation isothermal remanence (ISR) values are ≳0.5 compared to values <0.05 for most other naturally magnetized materials. The behavior of the lodestone magnetization has been studied from 4 K to 825 K, and x-ray, optical and transmission electron microscopy data have been used to confirm the γ-FeO3-Fe3O4 epitaxy. On heating to 250 °C coercive force (HC), remanent coercive force (HR), and ISR decrease, while about 70% of the NRM is lost. On returning to ambient temperature an increase in saturation magnetization (IS) is noted which can be interpreted as an ordering of the γ Fe2O3. Further heating to 425 °C results in destruction of the γ Fe2O3, a complete destruction of the lodestone remanence, while Hc, HR, and ISR increase. Beyond 425 °C the material behaves normally. On returning to ambient temperatre Hc and HR recover in smooth and continuous fashion while the thermoremanence (TRM) acquired in the geomagnetic field is less than 5% of the NRM value. Initial and final HC and HR values are the same. However as the thickness of the γ Fe2O3 lamellae increase the final HC and HR values are reduced. IS is reduced by an amount dependent on the γ Fe2O3?αFe2O3 conversion. The intense lodestone remanence was apparently acquired during the oxidation of Fe3O4, though the lodestone could be charged by fields associated with a lightening discharge.
Magnetostatic wave to exchange resonance coupling
Authors: Adam J. D. , O’Keeffe T. W. , Patterson R. W.
Published: February 2003

Coupling of propagating magnetostatic waves with resonant exchange dominated spin wave modes produces attenuation notches in the magnetostatic wave transmission response. The exchange resonances occur when kex=nπ/d, where kex is the exchange wave number normal to the film plane, n is the mode number and d is the thickness of the epitaxial YIG film. Measurements of attenuation notch depth and position have been performed on as grown LPE-YIG films and on films whose surface spins were pinned by ion milling, SiO2 deposition or annealing. Coupling was strongest for magnetostatic volume waves with the magnetic bias field normal to the film. Coupling to magnetostatic surface waves was less strong and in accordance with theory magnetostatic volume waves propagating parallel to the magnetic bias field showed zero coupling. The various treatments increased the depth of the attenuation notches and produced a mode pattern consistent with spin pinning asymmetric between the two film surfaces. The probable source of coupling between the propagating magnetostatic waves and resonant exchange modes in as grown films are magnetic non-uniformities in the YIG films due to transient layer or melt depletion effects.
Theory for magnetostatic forward volume wave excitation
Authors: Parekh J. P.
Published: February 2003

The present paper reports a theory for the excitation of magnetostatic forward volume waves (MSFVW’s) in YIG films by the most basic of all transducers, viz., an electric line current source, and various ramifications thereof (microstrip, meander-line and grating couplers). Expressions for power in the MSFVW’s excited by these transducers are derived, and computations of the transducer excitation characteristics are presented. It is found that all transducers yield a significant excitation of higher-order MSFVW’s, with the best suppression of these modes provided by the single microstrip coupler.
Bandpass filtering and input impedance characterization for driven multielement transducer pair-delay line magnetostatic wave devices
Authors: Wu H. J. , Smith C. V. , Owens J. M.
Published: February 2003

This paper reports results of theoretical and experimental studies of microwave delay line filters based on magnetostatic wave (MSW) propagation in epitaxial yttrium iron garnet (YIG) with multielement transducer pairs for wave launching and receiving. Filter transmission and input impedance characteristics for both magnetostatic surface wave (MSSW) and magnetostatic forward volume wave (MSFVW) devices have been calculated and measured experimentally. A planar, multilayer metal-dielectric-YIG geometry, permitting consideration of decoupling due to spacing between the transducers and YIG surface, is used to model the transducer. A ’’low’’ loss microstrip transmission line model is used to derive an equivalent transducer circuit. For assumed noninteraction of transducer element currents, the Poynting vector is used to determine the radiation resistance and the radiation reactance is derived from the Hilbert transform of this resistance. Experimental swept frequency measurements of insertion loss and input impedance versus frequency at S band have yielded experimental results which show good agreement with theoretical predictions of the model for a number of different configurations.
Apodization of variable coupling MSSW transducers
Authors: Sethares J. C. , Weinberg I. J.
Published: February 2003

Magnetostatic surface wave transducer theory is extended to include apodization and variable coupling. Results are presented for three types of apodization: conducting strip length, width weighting, and variable periodicity. An independent strip and a truncated array model are included. The dependence of radiation resistance on liftoff is exponential when there are no ground planes.
Ternary and quaternary rare earth cobalt magnetic materials with low reversible temperature coefficients
Authors: Gupta N. , Martis R. J. J. , Sankar S. G. , Rao V. U. S.
Published: February 2003

Permanent magnets made from SmCo5 exhibit negative reversible change in magnetization with increasing temperature, typically of the order of 0.04% per degree between −100 and +200°C. For special applications in precision instruments such as gyros and accelerometers it is desirable to reduce considerably the temperature coefficient of magnetization. Earlier studies have indicated that good temperature-compensated magnets may be prepared by replacing a part of Sm in SmCo5 with other heavy rare earth atoms such as Gd, Dy, Ho and Er. In the present study a number of compositions of the type SmxRl−xCo5 [R = Gd, Dy, Ho, Er, Tm, Yb, and Ti], (SmGd) Co5−yFey and Sm0.6 (R′Gd)0.4Co5 [R′ =Dy, Ho, Er] were prepared and examined by a number of techniques. X-ray diffraction patterns indicated the formation of essentially single phases in many of these compositions. Saturation magnetization, remanance, coercive force, anisotropy field and energy product of these materials at room temperature are reported. Magnetization measurements were performed in the temperature range −100 to +200°C and the values of α (reversible temperature coefficient of magnetization) were determined. As an illustration, for a material of composition Er0.2Sm0.8Co5.2 we observed the following results: 4πMs=11.6 kG, Br=11.1 kG, Hci =8.6 kOe and (BH)max = 17 MGOe at room temperature. The values of α observed are 0.025 between 150–225 K, 0.008 between 225–300 K and −0.009 between 300 and 375 K. Results for other compositions and their systematic trends are discussed.
An electron microscope study of the structure and morphology of a magnetically hard PtCo alloy
Authors: Hadjipanayis G. , Gaunt P.
Published: February 2003

Alloys near the composition PtCo can be quenched to retain a disordered fcc phase. Aging at a suitable temperature produces an ordered tetragonal phase of type AuCuI. The C axis is an easy axis of magnetization with an anisotropy constant of ∼ 107 erg cm−3. Aging produces a magnetically hard alloy. In the early stages of aging ordered regions of diameter 50–100Å were found with their C axes oriented at random parallel to one or other of the three original disordered cubic ′a′ axes. In the optimum high coercivity state particles of like C axis (diameter ∼200Å) group together on {110} planes; the c axis being at 45° to the {110} plane. In the overaged state like particles merge to form lamellae of one particular C axis the other orientations being consumed. Approaches to a better understanding of the hardening process are discussed.
Effects of internal oxidation and nitridation on the magnetic properties of non-oriented electrical steels
Authors: Geiger A. L.
Published: February 2003

The quantitative effects of internal oxidation and nitridation on the core loss and a-c permeability of several silicon-aluminum non-oriented electrical steels are described. Zones of internal oxidation have a large and relatively constant effect on the magnetic properties of alloys containing a wide range of silicon concentrations. For 0.64 mm sheet composed of alloys containing 0.5 to 2.5 percent silicon, oxide subscales increase the 1.5 T, 60 Hz core loss from 0.05 to 0.07 W/kg per μm of subscale thickness. Zones of internal nitridation in aluminum-bearing alloys have a different influence depending on the size and distribution of the nitride precipitates. Zones of internal nitridation in which the individual precipitates have linear dimensions from 0.1 to 1 μm increase the 1.5 T, 60 Hz core loss of 0.64 mm sheet by 0.015 to 0.07 W/kg. Subscales composed of coarse nitrides having maximum linear dimensions from 2 to 7 μm do not increase the core loss significantly.
Effect of vanadium on the magnetic properties of Al-killed low carbon steel
Authors: Rastogi P. K.
Published: February 2003

An investigation was made to examine the influence of V levels up to 0.10 w/o on the magnetic properties of Al-killed low carbon steels having 0.052/0.054 initial C, 0.36/0.37 Mn, 0.11/0.12 P, 0.022/0.024 S and 0.028/0.031 w/o Al. The processing sequence for these steels involved hot rolling, pickling, hot band annealing, cold rolling and high temperature annealing following decarburization. The results showed that the longitudinal permeability at 17 and 18 kG increases sharply with the addition of V up to 0.10 w/o. In contrast to improved permeability, the 15 kG core loss is essentially unaffected by changes in V concentration. According to the classical model, the computed anomalous loss in these steels constitutes approximately 25% of the total loss, which is a characteristic of the grain-oriented steel. Improvements in high induction permeabilities are directly related to the increase in B10 (induction at 10 Oe) which describes the sharpness of the Goss-texture. This relationship implies that the presence of V is required to develop a sharper Goss-texture in the steel. Electronmicroscopy results suggest that this texture is formed as a result of the precipitation of fine VN particles.
Magnetostriction in excess iron NiZnCo ferrite
Authors: Stakelon T. S.
Published: February 2003

Saturation magnetostriction was measured in polycrystalline excess-iron NiZnCo ferrite over a broad range in compositions. The stoichiometric compositions were Ni2+1−x−y−z Zn2+xCo2+yFe2+zFe3+2O4 where 0<x<0.63, 0<y<0.019, 0.11<z<0.57. By oxidizing the samples, the Fe2+ content was varied for a given molar composition from nearly the maximum allowable (stoichiometric) to 1% of this maximum (oxidized). This study presents the first magnetostriction measurements on oxidized ferrite, which is used extensively in devices due to its low magnetic loss. A single ion model of the magnetostrictive contributions of Fe2+, Fe3+, Ni2+, and Co2+ ions is formulated and compared to the data.
Reliable propagation of magnetic bubbles with 8 μm period ion implanted propagation patterns
Authors: Nelson T. J. , Wolfe R. , Blank S. L. , Johnson W. A.
Published: February 2003

Ion implanted propagation patterns for magnetic bubble devices provide an approach to higher density through relaxed photolithography. At the same time, the drive field requirements may be reduced, with respect to Permalloy based field access devices. Propagation is studied in the present work at 8 μm period in YSmLuCaGe films. Profiling by relative etch rate and by wafer curvature has led to 80/Ne/1-2E14+270/Ne/2E14+130/H2/2E16 implantation conditions. Bias field margins vs drive field for 27-step loops with neighbors on 2 λ centers and in orthogonal orientations on the wafer are presented to demonstrate the feasibility of major-minor loop organized chips. Crystal symmetry effects do cause the margins for differently oriented loops to be different in the present material, however. The overlap bias range is about 20 Oe extending downward from free bubble collapse. The minimum drive at 40°C appears to be about 35 Oe. Bias margins at 40 Oe drive taken over the temperature range 0–80°C show no anomalies for either orientation. Long term retention has been demonstrated for up to (10)8 cycles at 50 kHz, 40 Oe drive and 40°C.
Effects of ion implantation on the uniaxial anisotropy energy of a magnetic bubble film
Authors: Omaggio J. P. , Wigen P. E.
Published: February 2003

The effects on ion implantation on the uniaxial anisotropy energy of a magnetic bubble film have been studied. The films have been implanted with 800 KeV helium ions at doses from 1015 to 3×1016 ions/cm2. The mean projected range for these implantations is 1.9 μm which is 86% of the film thickness. The films exhibit multi-resonance FMR spectra which indicate an appreciable variation of Hu-4πM across the film thickness. FMR measurements in conjunction with an acid etching experiment were used to develop a model of this variation of the internal field. The resulting profile indicates the existance of a ’’bulk’’ region (∼70% of film thickness) where Hu-4πM is relatively constant but appreciably different from that of an unimplanted film. The variation of the anisotropy constant, Ku, as a function of implant dose is studied for this bulk region. Heavily implanted samples also show evidence of a narrow layer where Hu-4πM has changed greatly from the unimplanted value. This ’’well’’ in the Hu-4πM profile is deep enough to trap as many as four spin wave modes. The variation of 4πM (using a vibrating sample magnetometer) with implantation dose was also measured. These effects are interpreted in terms of lattice damage incurred during implantation.
Abstract: Magnetocrystalline anisotropy in mixed garnet thin films
Authors: Gangulee A. , Kobliska R. J.
Published: February 2003

We have measured the values of K1 in films grown on (100) and (111) oriented gadolinium gallium garnet substrates from PbO:B2O3:Fe2O3 fluxed melts. The values of K1 for each composition, obtained by different methods from films with different orientations, are consistent within themselves but are significantly smaller in magnitude than what would be expected from linear extrapolation of the K1’s of pure rare earth-iron garnets. (AIP)
Multilayer self-structured bubble memories
Authors: Kamin M. , Krawczak J. A. , Lins S. J. , Torok E. J. , Stermer R. L.
Published: February 2003

In bubble devices, the capacity per chip and chip yield are limited by the photolithographic resolution attainable. Recent work on gap tolerant structures attempts to address this problem. It is suggested, however, that to significantly increase this limit it is necessary to control a number of bubbles per geometric feature. We have initiated research into multilayered self-structured bubble memories which is based on this idea. Multilayered self-structured bubble memories have two or more coupled magnetic garnet layers grown on a common substrate. One layer, referred to as the data layer, supports bubbles encoded with data. One or more garnet layers, carrier layers, contain arrays of stripes or bubbles and determine the position of the bubbles in the data layer. Propagation of the data is accomplished by moving the domain arrays in the carrier layers. A study of several device configurations was accomplished and devices using a stripe domain carrier layer were selected for experimental work. Multilayer structures were grown having two magnetic layers with and without an epitaxial GGG spacer. Thickness, composition, and Q were varied from sample to sample. Propagation has been demonstrated using field access and current access devices moving the stripe domain ends. The magnetic coupling between the carrier stripe domain and the data bubbles was investigated and propagation of bubbles attached to the carrier stripe demonstrated. Chevrons were found to be more effective than semidisks, contiguous disks, or angelfish. Current access devices using a two-level two-phase stripline were found to be capable of generating and propagating stripes. A single-layer two-phase serpentine array requiring a single evaporation was also successful. These results indicate the potential of multilayer structures for high density high capacity bubble memories.
Abstract: A new single level masking approach to the fabrication of a magnetic bubble memory chip
Authors: Nishida H. , Asano A. , Tsumita N. , Hiroshima M. , Sugita Y.
Published: February 2003

We have developed a new method for the fabrication of the magnetic bubble memory chip which enables the realization of a memory chip with two separate levels of fine overlay patterns (Permalloy propagation and Al-Cu conductor patterns) by employing a single level masking process. To fabricate a memory chip, four levels of thin films (SiO2, Al-Cu, SiO2 and Permalloy) were coated on the bubble material first; then the photoresist patterns were delineated on top of these films. (AIP)
Design and development of single-layer, ion-implantable small bubble materials for magnetic bubble devices
Authors: Blank S. L. , Wolfe R. , Luther L. C. , LeCraw R. C. , Nelson T. J. , Biolsi W. A.
Published: February 2003

The general magnetic and physical requirements that a material must meet in order to be useful in magnetic bubble devices are reviewed. An approximate expression relating stripe width and film thickness to the material length parameter (ℓ) is presented. The well-known equations relating anisotropy, moment, Q factor and exchange constant are rearranged, and, combined with the approximate expression for ℓ, result in a convenient set of equations which are useful for materials design and for evaluating magnetic property measurements. The exchange constant (A) of epitaxial bubble garnet films is presented as a function of Curie temperature. Nominal compositions are given in the (YLuSmCa)3(FeGe)5O12 system which will support bubble diameters from 3.0–1.7μm. The range of λ111 values which are needed to implement Ion Implanted Propagation Patterns (I2P2) is presented. An approach is presented for increasing the uniaxial anisotropy in the 〈111〉 crystallographic direction without significantly changing the damping factor of the material. This approach utilizes the ’’Lanthanum Effect’’, where La exhibits a zero B value in the phenomenological anisotropy expression. Nominal compositions are presented in the (LaLuSmCa)3(FeGe)5O12 and (LaLuSm)3(FeGa)5O12 systems which will support bubbles ranging from 1.7–1.1 μm. Bias margin and longevity data taken on I2P2 type circuits of 8 μm period and bias margin data on 6 μm and 4 μm period circuits are shown. Phase equilibria data in the system Flux-ΣLn2O3-Fe2O3 are presented.
Flux growth of (Ca,Ge) -substituted rare−earth iron garnets in the regular solution approximation
Authors: Gualtieri D. M.
Published: February 2003

The solubility parameters concept of regular solution theory has been extended to the growth from a PbO/B2O3 flux of (Ca,Ge) - substituted rare-earth iron garnets. Solubility parameters have been calculated for various oxides which are present in melts prepared for the LPE growth of these magnetic garnets. An excellent correlation is found between the logarithm of the distribution coefficient of a cation on the garnet dodecahedral sublattice ln Ki and the calculated partial molar heat of mixing of its oxide and the flux. The variation of the melt saturation temperature with type and quantity of solute oxide has also been calculated, as well as the variation of the saturation temperature with changes in flux composition. The small effect of La2O3 additions on the saturation temperature of PbO/B2O3 fluxed melts is easily understood in this thermochemical approach to LPE.
A FMR study on horizontally dipped LPE grown (La,Ga): YIG films
Authors: Algra H. A. , Robertson J. M.
Published: February 2003

A spin wave resonance study is presented on the variation of the anisotropy field in (La,Ga): YIG films as a function of the growth conditions. The homogeneity of a film depends strongly on the diameter and the axial rotation speed of the substrate, but also on the growth temperature. A series of films grown at one temperature and rotation speed, but with different deposition times show variations in the lattice mismatch, the average saturation magnetization and the uniaxial anisotropy. Based on the results of the experimental resonance spectra obtained by etching a thick film successively, it is found that the variations in the saturation magnetization as well as in the anisotropy field are restricted to a small region only (0,5 μm) next to the substrate. The experimental resonance spectra have been compared with numerically obtained predictions.
Quenching of coercive force in bubble films by domain wall restoring forces
Authors: Walling J. C.
Published: February 2003

A mechanism is proposed to account for the disparity between coercive force in bubble domain films as measured by hysteresis techniques, which employ an ac-bias field component to move the wall, from that measured in pulsed bubble propagation experiments. In the proposed mechanism the magnetic restoring forces, that resist coercivity produced distortions of the wall pattern, greatly reduce the time average lag of the wall position caused by coercivity, to the extent that the restoring forces dominate the actual or true coercive force. The coercive force, measured by the hysteresis method, is proportional to the time average hysteresis lag and is thus reduced or quenched by these restoring forces. In bubble propagation, on the other hand, the restoring forces that affect bubble propagation are absent. A formula which relates the coercive force measured by the two techniques is derived. The theory is tested with experimental data on 1.8-μm and 3-μm films of the composition {Y,Sm,Lu,Ca}3[Fe,Ge,Lu]2 (Fe,Ge)3O12.
Two devices for non-optical characterization of full wafer magnetic bubble films
Authors: Omaggio J. P. , Globe M. , Wigen P. E. , Mier M. G.
Published: February 2003

It has been shown [1] that measurements of the stripe collapse field, Hsc, zero magnetization susceptibility, χo and film thickness fully characterize the static properties of a magnetic bubble film. As part of an effort to develop non-optical, non-destructive means to make these measurements, a hysteresis loop tracer and microwave cavity for one inch bubble wafers have been designed and built. The hysteresis loop tracer allows measurement of χo and Hsc while the microwave cavity can be used for an alternate measurement of Hsc as well as a direct measure of Hu-4πM. The hysteresis loop tracer uses large amplitude (∼1000 Oe peak-peak) sinusoidal drive fields at 200 Hz to drive the sample’s magnetization. This changing magnetization induces a derivative signal in a sample pick up coil. Signal processing is automated and a desk top calculator gathers data, integrates and plots the hysteresis loop or its derivative. The microwave cavity has a resonant frequency of 9 GHz and one inch wafers are mounted outside the cavity wall.
Abstract: Ellipsometric measurement of magnetic bubble films
Authors: Mier M. G. , Blasingame J. M.
Published: February 2003

Optical ellipsometric measurements of film thickness and refractive index are reported for single-, double- and triple-layer films of bubble materials of widely different composition and thickness. Comparison with thickness determinations by reflection spectroscopy, using assumed or measured refractive indices, shows excellent agreement. (AIP)
Micromagnetic analysis of S=1 magnetic bubbles with curvature effects
Authors: Blake T. G. W. , Della Torre E.
Published: February 2003

The micromagnetic model of Della Torre et al. [7] has been extended to include the analysis of bubble collapse and runout and to reduce computation times by making radius corrections. Results were obtained for a range of bubble aspect ratios and quantities describing wall bulging, flaring, and twisting were computed. Data on material parameter effects is also presented. Magnetization orientation angle contour maps over the r-z plane in the wall region are presented. Wall structure was found to depend strongly on bubble aspect ratio as well as on material parameters. Wall bulging increases with decreasing bubble aspect ratio; at Q=2.3, it is about 5% of the bubble radius near collapse, and 1.5% near runout. The wall thickness at the film center is characteristic of a Bloch wall, but near the surface, azimuthal twisting and wall width flaring increase with bubble aspect ratio. Calculated wall area energy densities are lower than those of corresponding wall structures of variational models. For Q=2.3, it was found that the range of bubble stability is smaller than in previous predictions.
Shape of bubbles
Authors: Nedlin G. M.
Published: February 2003

The general form of the equation of motion of an arbitrary domain wall is obtained for materials within the uniaxial anisotropy constant K≫2πM2 (M is the magnetization). In the particular case of a static bubble it leads to the equilibrium equation, determining the dependence of the bubble radius R(z) on the coordinate z along the film thickness. This equation does not have a solution R(z) = constant, i.e. bubbles cannot be cylindrical, but have to be bent.
Two-dimensional magnetostatic resonances in a thin film disk containing a magnetic bubble
Authors: Morgenthaler F. R.
Published: February 2003

We have recently discussed magnetostatic modes in a normally-magnetized, thin-film disk that are bound to ’’virtual-surfaces’’ created by the presence of a radial dc-field gradient; the frequency and polarization of such modes was found to be sensitive function of the gradient. We now employ a similar method of analysis to study two-dimensional resonance modes in a thin film contaning a single magnetic bubble. When the thickness of the bubble domain wall is ignored, and there is no applied gradient, the spectrum, as expected, contains single bubble resonances coupled to disk resonances. However, actual domain walls contain large magnetic anisotropy field gradients due to the often complex spin reversal pattern. Such gradients will affect the mode polarization within the wall and the effective boundary conditions acting across the wall may be significantly altered for those resonances coupled to exchange modes within the domain wall. The related but simpler problem of rf exchange modes generated at a plane ’’virtual-surface’’ within a single domain region is studied in detail.
Abstract: Bias field dependence of domain drag propagated bubble domains
Authors: DeLuca J. C. , Gambino R. J.
Published: February 2003

Bubble propagation by the domain drag effect is studied as a function of bias field (Hb) in a GdCoAu amorphous film with pulse widths of 20, 40, and 50 ns and current densities in the 4×106 to 7×106 amp/cm2 range by pulsing currents directly through a stripline of amorphous material containing hexagonal arrays of bubbles. With 0<Hb<500 Oe the bubble velocity is largely independent of bias field remaining constant at a value of 65 m/sec; as the bias field is increased above 500 Oe the velocity decreases gradually through a minimum of 35 m/sec at 1100 Oe and then increases to 65 m/sec at Hb=1440 Oe.(AIP)
A novel major/minor loop bubble memory chip organization for high performance without block replication
Authors: Bonyhard P. I.
Published: February 2003

Bubble memory chips were originally organized with reentrant major loops, but presently the tendency is towards a block replicate organization, because of the latter’s better performance and data integrity protection. However, as shown in this paper, all the advantages of the block replicate organization, and more, can be realized by a novel organization that still uses reentrant major loops and no block replication. This organization features a direct path from the generator to the detector, two replicate/swap gates coupling that path to a pair of reentrant major loops, and double period swap gates coupling the major loops to the minor loops. As a result, average access and request cycle times are reduced to 65% and 75%, respectively, of their previous best values for the same chip capacity, and potential volatility problems are eliminated.
Induced magnetic form factor of Ce0.736Th0.264
Authors: Moon R. M. , Koehler W. C.
Published: February 2003

The polarized neutron technique has been used to study the spatial dependence of the induced magnetization in the alloy Ce0.736Th0.264 in both the γ and α phases. In the γ phase we observe a susceptibility in good agreement with bulk susceptibility measurements and with a Q dependence characteristic of Ce3+. In the α phase a different Q dependence is observed which may be caused by a contribution to the susceptibility by the conduction electrons.
Temperature dependence of the field induced magnetic form factor of CeSn3
Authors: Stassis C. , Loong C.-K , McMasters O. D. , Moon R. M.
Published: February 2003

Polarized neutron scattering techniques have been used to study the spatial distribution and temperature dependence of the magnetization induced in a single crystal of CeSn3 by a magnetic field of 42.5 kG. We find that in the 300–40 K temperature range the measured form factor is in good agreement with the free ion 4f magnetic form factor of Ce3+. Below 40 K large deviations from a 4f magnetic form factor were observed. A satisfactory fit to the data below 40 K can be obtained by assuming that the induced magnetization contains a large component of 5d electronic character of eg symmetry.
Single crystal holmium iron garnet : Anomalous behaviour of the Faraday rotation
Authors: Fadly M. , Guillot M. , Feldmann P. , Le Gall H. , Makram H.
Published: February 2003

The magnetic properties (spontaneous magnetization and susceptibility) and the Faraday rotation behaviour (at 1.15 μm wavelength) are reported on single crystal holmium iron garnet (HoIG) under fields up to 30 kOe applied along the three crystallographic directions : ‖111‖ ‖110‖ and ‖100‖ in the 4.2–300 K range. The evolution of the Faraday rotation is strongly anisotropic even in the temperature ranges where the magnetic properties are found to be isotropic. For the rare earth, the electric dipole contribution to the Faraday rotation is a strongly temperature and applied field dependent function which appears to be different in the two regions separated by the compensation temperture (137 K).
Magnetic properties of single crystal erbium iron garnet
Authors: Guillot M. , Marchand A. , Feldmann P. , Le Gall H. , Desvignes J. M.
Published: February 2003

Magnetization and susceptibility measurements performed on single crystal Erbium Iron Garnet (ErIG) are presented over the temperature range 4.2–6O0 K in a field up to 30 kOe applied along the [111] direction. Important differences from polycrystalline sample results are obtained. The magnetic susceptibility follows a Curie Weiss law; but two values of the paramagnetic Curie temperature and of the Curie constant in the two temperature ranges separated by the compensation temperature are found. At low temperature, the exchange interactions between Er3+ ions are not negligible compared to the iron–rare earth interactions. The molecular field coefficient which represents these last interactions is found to be strongly temperature dependent.
Boundary effects in magnetic insulator thin films
Authors: Summers H. R. , Wigen P. E.
Published: February 2003

The angular variation and frequency dependence of the boundary condition have been investigated in single crystal LPE and CVD thin films of Yttrium Iron Garnet. Data have been analyzed as a function of frequency at 5.95 GHz, 9.1 GHz, and 23.4 GHz and over a temperature range of 40 K to 300 K. Previous work has proposed that a uniaxial surface anisotropy energy would produce a ’’non-parallel’’ ground state with the spins near the surface tending to align at angles canted with respect to the bulk. This ’’non-parallel’’ ground state predicts a frequency dependence and an angle dependence in the boundary condition which has been verified by the data. Additionally, the difference in the magnitudes of the g-values and of the spin moments of the gadolinium and the iron ions at the interface surface will contribute an isotropic term to the boundary condition. Its frequency dependence due to the susceptibility of the gadolinium spins has been observed.
Abstract: One-ion mechanism of magnetocrystalline surface anisotropy energy: Yttrium iron garnet
Authors: Rado George T.
Published: February 2003

The present paper reports a simple but quantitative calculation of surface anisotropy on the basis of a ’’one-ion’’ mechanism. (AIP)
Magnetic properties of DyFe2H2 from 57Fe, 161Dy Mössbauer effect and magnetization measurements
Authors: Viccaro P. J. , Friedt J. M. , Niarchos D. , Dunlap B. D. , Shenoy G. K. , Aldred A. T. , Westlake D. G.
Published: February 2003

A single phase stable hydride with nominal composition DyFe2H2 is shown to have the cubic C15 Laves structure with a 5% larger lattice constant. 57Fe Mössbauer spectra show two sites with nearly equal population and with different isomer shifts and hyperfine fields. Based on the average hyperfine field at 4.2 K, an Fe moment of approximately 1.6 μB is estimated. From the 161Dy data at 4.2 K, which show a single site, a nearly free-ion moment of 9.8 μB is determined. Relaxation effects in the 161Dy spectra above 77 K, combined with a sharp decrease in the moment with increasing temperature, imply a weakening of the Dy-Fe magnetic coupling induced by the presence of the hydrogen.
Optical probing of magnetoelastic Rayleigh waves
Authors: Volluet G.
Published: February 2003

Magnetoelastic surface waves have been propagated in an epitaxial Gd-Ga doped YIG film using piezoelectric ZnO layer and interdigital transducers for launching Rayleigh waves at 339.9MHz. An in-plane applied magnetic field has been adjusted to obtain the magnetoelastic (ME) interaction; in this case the waves become leaky. Such an interaction has been investigated by optical diffraction in the Raman-Nath region with a polarized laser beam (6 328 Å). A diffracted light, cross-polarized with respect to the input, has been detected when the ME interaction exists. This signal due to the magnetic part of the wave can be used to study the characteristics of the interaction. The saturation threshold in acoustic power has been measured. Then the behavior of the ME interaction as a function of the magnetic field has been observed at different distances along the propagation path. The imaginary part (Im.k) of the wave number k due to the leaky character of the interaction has been measured. Moreover it is seen that the dynamic magnetization components can be analysed by Faraday and Cotton-Mouton effects.
Effect of electron correlations on photoemission from narrow-band metals
Authors: Davis L. C. , Feldkamp L. A.
Published: February 2003

Recent angle-resolved photoemission measurements on Cu and Ni suggest the importance of electron correlations not included in band calculations. To study these effects, we have calculated the photoemission spectrum for the single-band, strongly ferromagnetic Hubbard model. A hole in the ↑ band is viewed as a core hole which can hop from site to site. For a strong interaction U, a bound level exists below the ↓ band at the site of the spin ↑ hole. The photoemission spectrum consists of a main line (bound level occupied in final state) and a satellite (bound level unoccupied). The binding energy of the satellite is about U larger than that of the main line. The intensity of the main line is approximately n↓, the fractional occupancy of the spin ↓ band. We identify the spin ↑ band (inferred from experiment) with the peak position of the main line as a function of the momentum k↘ transferred to the solid. The ratio of inferred band width to bare band width is approximately n↓. Since the 3d-bands are filled in Cu, no such band renormalization can occur for it. Strong electron correlations are also responsible for the small exchange splitting in Ni.
The uses of pulsed neutron sources for research in magnetism and other areas of condensed matter physics
Authors: Sinha S. K.
Published: February 2003

The next decade will see the development worldwide of pulsed spallation neutron sources for condensed matter research. A conceptual introduction to such neutron sources is given. Neutron time-of-flight techniques as applied to diffraction and inelastic neutron scattering spectroscopy are discussed, and compared with techniques using crystal spectrometers. The advantages of such sources such as high effective thermal and higher energy neutron fluxes for certain kinds of experiments are discussed. The applications of these sources to various areas of condensed matter research are reviewed, with special emphasis on the study of magnetism. Finally, a brief account is given of the status of pulsed spallation source development around the world.
Magnetic ordering phenomena in TmS
Authors: Koehler W. C. , Moon R. M. , Holtzberg F.
Published: February 2003

Neutron diffraction data have been obtained from powder and single crystal specimens of TmS at temperatures ranging from room temperature to 1.7 K and in applied magnetic fields up to 42.8 kOe. In zero field TmS undergoes a transition, at about 8.9 K, to an antiferromagnetic structure which is almost the type two face-centered cubic structure. In this structure there are four G-type or (π,π,π) type antiferromagnetic sublattices such that the moments are parallel in (111) planes, alternating in sign from one such plane to the next. Superimposed on the ordering is a sinusoidal modulation with propagation vectors parallel to [110] directions. The structure is a multidomain one which gives rise to a very complex diffraction pattern. With polarization analysis it was possible to determine the moment directions in the domains. For example, in domains with propagation vector parallel to [11̄0] the moments are parallel to [112̄]. From powder data taken at 1.7 K the maximum value of the Tm moment was estimated to be 4.0 μB. Diffuse streaks of magnetic origin with temperature and field dependence different from that of the satellites were observed which may influence our estimate of the magnitude of the ordered moment. The response of the magnetic reflections to applied magnetic fields can be understood, in part, in terms of domain repopulation.
Magnetic interactions in R6Mn23 rare earth intermetallics
Authors: Delapalme A. , Déportes J. , Lemaire R. , Hardman K. , James W. J.
Published: February 2003

Polarized neutron experiments on a single crystal of Y6Mn23 give evidence for a ferrimagnetic arrangement of Mn atoms. The value of the Mn moment depends on the crystallographic site. Magnetization measurements at low temperature suggest non-collinear magnetic structures for single crystals of Gd6Mn23, Dy6Mn23, and Er6Mn23. The non-collinearity results from the effects of negative R-R interactions and the crystal field.
Abstract: Neutron diffraction study of HoRh4B4
Authors: Lander G. H. , Sinha S. K. , Fradin F. Y.
Published: February 2003

Our measurements show that HoRh4B4 is ferromagnetic TC= (6.8±0.2) K with the moment parallel to the unique c tetragonal axis. (AIP)
Temperature dependence of the samarium magnetic form factor in SmCo5
Authors: Givord D. , Laforest J. , Schweizer J. , Tasset F.
Published: February 2003

Results of polarized neutron experiments on SmCo5 at 4.2 K and 300 K are reported. To overcome the problem of the huge Sm absorption the measurements were made at short wavelengths, but on a single crystal containing natural samarium. The Co moments are close to those found in YCo5. The Sm form factor is very different at 4.2 K and 300 K, giving direct evidence for exchange and crystal field mixing of excited multiplets into the ground multiplet. The Sm moment is smaller at 300 K than at 4.2 K and its orbital character is less pronounced. The cross-over is calculated to occur at 350 K above which temperature the spin contribution exceeds the orbital one. The compound is ferromagnetic below the cross-over and ferrimagnetic above. The exchange and crystal field parameters deduced from our results are in agreement with previous determinations [1].
Weak ferromagnetism in Co (CH3COO)2⋅4H2O below 85 mK
Authors: Karnezos M. , Lecomte G. , Friedberg S. A.
Published: February 2003

The magnetic susceptibilities of monoclinic crystals of Co (CH3COO)2⋅4H2O have been measured between 0.05 and 4.2 K in a 3He-4He dilution refrigerator by a mutual inductance method at 70 Hz. The data indicate antiferromagnetic ordering below TN?85 mK with the preferred spin direction near the a-axis but with spins canted toward the b-axis, producing a weak ferromagnetic moment in that direction. Both antisymmetric superexchange interaction and anisotropy of the ionic moment at inequivalent sites within the unit cell are believed to contribute to this canting. Principal axes of the macroscopic susceptibility tensor have been determined above TN. Estimates of the principal values of the g-tensor of the Co++ ion in its ground state are given.