bluuebunny/crossref_metadata_2025 huggingface dataset:
Abstract: Bubble chip planar fabrication techniques
Authors: Bailey R. F.
Published: February 2003

These results will show that for specific switch designs, the planar permalloy requires considerably less drive field than its non-planar counterpart; further, the increase in conductor pattern cross-section for given lithography requirements will become increasingly important as the bubble device period is reduced or the chip size (capacity) is increased. A planar process developed at Rockwell is designed to also reduce thermal gradients on large area chips caused by localized heat sources such as power dissipation in the detectors. (AIP)
Abstract: Ion beam etching equipment for production of bubble memory devices
Authors: Monk G. W. , Thompson G. R.
Published: February 2003

This paper will review the important characteristics of ion beam etching, how they have affected the current state of production equipment and review some important factors that may determine future capabilities. A typical ion beam etching system consists of a gun or ion source operating at 4×10−5 torr, a work chamber at 7×10−5 torr, a fixture for the wafers, a vacuum system, a power supply for the gun, and a means of monitoring the etching progress; the main difference between ion beam etching and conventional sputter etching is the use of a directed ion beam and a work chamber at a relatively low pressure. (AIP)
Abstract: A new approach to bubble propagation modelling
Authors: van den Berg H. A. M. , Zieren V. , de Vries G. W.
Published: February 2003

A new approach to the theory of the modelling of the interaction between bubbles and the permalloy circuit-elements in bubble devices will be given; it will be demonstrated experimentally as well as theoretically that effects which have not been taken into account until now, positively influence the bubble propagation. A theoretical model is presented with whose help the magnetization distribution can be calculated; in contradiction to the current opinion it will be shown that a great deal of the flux of the bubble punches through the permalloy although the contribution of the vertical component cannot be ignored. (AIP)
Past, present and future small-bubble-diameter magnetic memory materials
Authors: Kestigian M. , Smith A. B. , Bekebrede W. R.
Published: February 2003

To be competitive with existing and future planned mass-storage memories, cylindrical domain devices will require magnetic compositions which possess higher capabilities than those currently available. This discussion describes the more important parameters which must be known and controlled in the development of improved small-bubble diameter materials. A quick review of small-bubble-diameter compositions is presented. The body of the discussion emphasizes the status of small-bubble diameter materials. The optimum small-bubble-diameter liquid-phase epitaxial composition can be obtained only by the consideration of a number of interrelated parameters. The relationships of these variables are discussed in detail, as are the resultant effects on device performance. A look into future small-bubble-diameter garnet compositions and potential substitute bubble materials is included.
Complementary σ-bubbles in bubble automotion
Authors: Iwata S. , Shiomi S. , Uchiyama S. , Fujii T.
Published: February 2003

In this paper is reported the existence of two kinds of complementary σ bubbles together with properties of the automotion of these bubbles. These bubbles are distinguished by σs and σf, and the speed of the automotion of σf is always faster than σs if the driving conditions are the same. From the dynamic properties measured, the wall structures for σs and σf are suggested to be S=1, L=2 and S=0, L=4, respectively, where S is the winding number of the bubble domain wall and L is the number of Bloch lines in the wall. The methods of obtaining σs and σf are also described.
Bubble wall-state coding
Authors: Hannon D. M. , Hu H. L.
Published: February 2003

Coding of bubble wall states in a current access device is described. Two wall-coding geometries have been used, a 50 μm wide conductor and a 15 μm conductor with a 5 μm gap in the center. The margins of in-plane field versus current for S=0 and S=1 bubbles are given. The S=0 margin is reasonably well understood. For successful S=0 coding the sum of the external in-plane field and the field from the coding conductor must be greater than the upper cap-switch field. The S=1 margin is quite narrow in current and is not understood. At mid margin both S=1 and S=0 bubbles have been coded 108 times without error.
Influence of NiFe quality on bubble devices
Authors: Cohen M. S. , Beall G. W. , Kryder M. H. , Mazzeo N. J. , Collins T. W.
Published: February 2003

It is anticipated that as the period of bubble devices decreases, undesired effects due to loss of permeability of the NiFe overlay will become increasingly important, even for half-disk elements. The failure mechanism of ’’I-bar crossing ’’ in H-I tracks, which leads to high values of the minimum drive field Hxy(min), was studied for both 8 and 20 μm bubble periods as a means of gaining insight into such effects. Direct Ferrofluid observations, along with measurements of the parameter Hbb1 which characterizes the coercivity of an individual H bar, confirmed that the I-bar crossing phenomenon originated in high coercivity, and hence high remanence and low permeability of the NiFe. This interpretation was supported by a study of the effects on a sample of a series of annealing treatments at increasing temperatures, a process known to increase NiFe coercivity. The annealing studies demonstrated that for a given NiFe thickness Hbbl was better correlated with Hxy(min) than was the sheet-film coercivity Hc, showing that measurements of Hc must be interpreted with caution. Furthermore it was found that Hbb1 and Hxy(min) decreased with increasing NiFe thickness.
Abstract: Gradientless propulsion for S=1 bubble in ion-implanted bubble garnets
Authors: Ju K. , Humphrey F. B.
Published: February 2003

Gradientless propulsion (automotion) of bubbles has been studied on a CaGe ion-implanted bubble garnet; three different stable S=1 states, as χ±= (1,0,0)± and σ−= (1,2,0)−, were found. The two χ bubbles automote in opposite direction normal to the in-plane field with χ+ moving along Hi×z; the σ− automote in the same direction as χ+ but at a different pulse bias field margin.(AIP)
256 kbit bubble memory chip fabrication and characterization
Authors: Tsuzuki N. , Yamamoto M. , Hyuga F.
Published: February 2003

A 256 kbit bubble memory chip, which uses asymmetric chevron propagation elements has been designed, fabricated and characterized. Average circuit period is 8 μm and minimum feature size is 1 μm for all chip functions. Chip size is 4.5 mm×5.1 mm. A new stretcher detector and a planar chip structure enable the 256 kbit chip to operate at low rotating field. For a typical device processed on a (YSmLu)3(FeGa)5O12 magnetic garnet film, the overall bias margin for all functions is 15 Oe with a 50 Oe circular rotating field at 200 kHz.
Interaction and longevity measurements in 67 kbit bubble device chips
Authors: Hagedorn F. B.
Published: February 2003

Bubble-bubble interaction and longevity measurements have been made on 67 kbit bubble device chips that were designed around asymmetric chevron propagation elements on a 16 μm period in a major line-minor loop organization. A nearest-neighbor interaction, whose magnitude is equivalent to 4.2 Oe of bias field, is clearly observed experimentally and is attributed to the simultaneous presence of nearest neighbor bubbles on a ’’C’’ shaped permalloy element in the swap gate of each minor loop. Evidence is also presented for weaker but definite interactions between second-nearest neighbor bubbles and between adjacent minor loops. Longevity measurements at 40°C and with a rotating field of 40 Oe at 50 kHz show this chip design to have at least 20 Oe of bias field margin for 105 write-read cycles, each of which contains 792 bits of information. Data are also presented on the longevity propagation characteristics of the individual minor loops.
Abstract: Fe hyperfine fields in Fe3−xVxSi alloys
Authors: Burch T. J. , Weiler C. A. , Raj K. , Budnick J. I. , Niculescu V. , Papefthymiou G. C. , Frankel R. B.
Published: February 2003

Measurement of the Mössbauer spectra of Fe in Fe3−xVxSi alloys for 0?x?1 at 4.2 K and room temperature show that the Fe (A, C) spectra become increasingly complex as x increases and then collapse into a single line at the highest concentration. Simulated spectra reflecting Fe (A, C) moment variations are compared with the actual spectra.(AIP)
Conduction electron-local moment interactions in metals via dHvA waveshape analysis
Authors: Lowndes D. H.
Published: February 2003

Detailed information about conduction electron-magnetic impurity interactions is contained in the harmonic content of the de Haas–van Alphen (dHvA) effect. Using the first three harmonics of the dHvA effect, the spin-up and spin-down conduction electron scattering rates, Xσ= (h//2πkB) 〈τ−1〉σ, may be separately determined, along with the magnitude of the conduction electron-local moment exchange energy shift, ΔEex=μBHex. Quantum oscillations arise from extremal orbits on the Fermi surface, so that the measured quantities are orbital averages, and one has available a spin-resolved, k-space spectrometer. Results obtained by applying dHvA waveshape analysis techniques to carry out a survey of conduction electron interactions with both d-shell (Cr, Fe, Co) and f-shell (Gd, Ho, Yb) moments in Au include: (1) The observation of strongly spin-dependent scattering (X↑≠ X↓) by d-shell impurities, in contrast to spin-independent scattering by f-shell impurities; (2) exchange energy shifts of both ferro- and antiferromagnetic sign for f-shell impurities, and about an order of magnitude smaller than the purely antiferromagnetic exchange observed for d-shell impurities; (3) observation of impurity-impurity interaction effects in Au (Co) at impurity concentrations ≲500 at. ppm; (4) evidence from partial wave analysis that the local moment-conduction electron interaction proceeds almost entirely via the d-wave part of the conduction electron wavefunctions.
Optical magnetization of a metal: Spin polarized photoemission from tungsten
Authors: Zürcher P. , Meier F.
Published: February 2003

Opitcal magnetization of a metal single crystal is observed for the first time by spin polarized photoemission. The (100) -surface of a tungsten crystal was irradiated by circularly polarized light and the spin polarization of the emitted photoelectrons was measured for light energies 1.5 eV?hν?5.6 eV. The polarization reaches a maximum of 8% and its sign changes as function of photon energy. In order to obtain photoemission from transitions between the spd-hybridized conduction bands, the work function had to be lowered by depositing cesium onto the surface. The successful outcome of this measurement opens the prospect to develop a new, spin-sensitive tool to explore electronic band structures.
Electronic structure of uranium selenide: Experiment and theory
Authors: Erbudak M. , Greuter F. , Meier F. , Reihl B. , Vogt O. , Keller J.
Published: February 2003

The spin polarization of the photoelectrons emitted from ferromagnetic USe has been measured for light energies 3.5<hν<11 eV. Over this whole range the majority of the photoelectrons has the spin magnetic moment directed opposite to the bulk magnetization. An energy scheme of USe is presented which is in agreement with the spin polarization results and measurements of the photoelectron energy distribution.
Abstract: Mixed valence: Comparison between Yb and Tm compounds
Authors: Lustfeld H.
Published: February 2003

Charge fluctuation processes of the type, fn→fn−1+particle-hole excitations, fn−1→fn+ particle-hole excitations, are most important in describing the properties of Yb mixed valent compounds. Mixed valent Tm compounds differ from the Yb compounds insofar as both occupations of the 4f-shell are magnetic, nevertheless, the processes remain important, and their influence on susceptibility and specific heat is discussed. (AIP)
Abstract: Band structure and Fermi surface of ferromagnetic gadolinium
Authors: Batallan F. , Sommers C.
Published: February 2003

We have studied the band structure and Fermi surface of ferromagnetic Gd using a KKR formalism coupled with a rigid band splitting; two separate calculations, one non-relativistic, the other relativistic were performed. Our bands are significantly different from most all the other calculations performed to date; an adjustment of 0.1 eV in the Fermi level brings our calculation into good agreement with experiment. (AIP)
Abstract: Anomalous subsidiary absorption butterfly curves in single crystal YIG at 9.16 GHz and 300 K
Authors: Patton Carl E. , Jantz Wolfgang
Published: February 2003

Anomalous structure in the microwave subsidiary absorption extending several hundred Oe below the butterfly curve minimum at HC was reported recently, but threshold fields (hc) were measured only over a limited field range. These data have been extended to cover the entire butterfly curve for sphere and plate samples. (AIP)
Static and dynamic neutron depolarization studies of ferromagnetic domain structures
Authors: Rekveldt M. Th. , van Schaik F. J.
Published: February 2003

A polarized neutron beam passes through a ferromagnetic sample. In front of the sample a polarization turner turns the polarization towards the x, y or z direction. A second polarization turner behind the sample enables one to analyse any component of the polarization vector. In this way a (3×3) depolarization matrix can be measured from which various domain quantities are determined in the bulk, such as the mean magnetization in three dimensions (Mi, i=x,y,z), the mean domain size and the mean local direction of magnetization within the domains. Applying a periodic magnetic field on the sample and using a multi-channel analyser the time dependent depolarization matrix determines the mean periodic time dependence of the parameters mentioned. Among the possible applications of the method static and dynamic experiments are discussed. Static experiments have been carried out on an oblate Ni ellipsoid with a magnetic field in the y-direction in the [311] crystal direction in the plane of the ellipsoid. From the positive sign of the z-magnetization at decreasing temperature below the Curie temperature it is deduced that the [111] direction is the easy direction of magnetization. Dynamic experiments have been carried out applying a block shaped periodic field on one leg of a FeSi(3.5 wt% Si) picture frame crystal. After a field reversal eddy currents confine domain nucleation to the surface only, which depolarize partly the various polarization components. After a time the nuclei on each crystal side grow together forming two rather wavy domain walls parallel to the surface moving to the centre from which the position, velocity of the walls and the distance between the initial nuclei have been determined.
Application of soliton theory to ferromagnetic domain wall dynamics
Authors: Paul D. I.
Published: February 2003

Consider the dynamics of a 180° ferromagnetic domain wall pinned by a planar defect. The defect is characterized by an abrupt change in both the magnetic anisotropy and exchange energies. General algebraic expressions are obtained for the resonant domain wall oscillation frequency, the effective wall stiffness, and the coercive force. The wall oscillation frequency due to a grain boundary in iron is computed as ∼400 Mc/s. in good agreement with typical experimental values of ∼500 Mc/s. Noting that, when an effective stiffness constant is added to the Hamiltonian, the zero energy Goldstone translation mode is raised to a finite energy level, we show that this excitation energy is proportional to the fractional change in the medium characteristics and to the anisotropy constant and that it has a maximum value when the ratio of defect width to domain wall width is of order unity.
Simulation of x-ray topographs of ferromagnetic domains in silicon-iron, especially their junctions
Authors: Nourtier C. , Kléman M. , Taupin D. , Miltat J. , Labrune M. , Epelboin Y.
Published: February 2003

Inhomogeneities of spin distribution are sources of magnetostrictive strains. An infinite 90° (110) Bloch wall in iron for instance acts as a small angle (λ100?3.10−5 rad) twin boundary and introduces a brutal rotation of the lattice. Wall junctions create long range inhomogeneous strains (and stresses). These quantities can be analysed in terms of dislocation densities and disclinations, which may be observed experimentally by X-ray (Lang) topography. This is illustrated here for the classical Dijkstra and Martius domain structure.
Hysteretic properties of permalloy I-bars
Authors: Huijer E. , Watson J. K.
Published: February 2003

Bitter solution observations and small-spot Kerr effect measurements have been used to study the response of 100×12×0.3 μm permalloy bars to applied fields that exceed the range of linear response. Bitter patterns showed that a uniform applied field of sufficient strength saturates the center part of the bar by displacing a domain wall to the side of the bar. After reducing the field below its saturation value, remanent magnetization is maintained by a ’’zig-zag’’ domain structure. The original domain pattern returns only at a certain lower value of applied field. An interpretation of the zig-zag pattern is given. The polar effect was used to detect the annihilation and reappearance of Bloch walls in two sets of specimens, in response to similar sequences of applied fields. Differences in the measured renucleation field are attributed to edge effects. As a matter of further interest, the positive or negative polarity of a Bloch wall was found to be correlated with the CW or CCW orientation of the domain structure of the I-bar.
Investigation of bubble stray field effect on the domain wall structure of the overlay bars by interference contrast technique
Authors: Khaiyer I.
Published: February 2003

The effect of bubble stray field on the magnetization distribution of a permalloy overlay bar is photographed by Interference Contrast Technique (ICT) in here and the results are compared to the experimental data available from the magneto-optical Kerr effect measurements. The 180° domain wall deformation and the resultant magnetic domain patterns due to a travelling bubble under an I bar is shown. The magnetization distribution curves along the I bar due to different positions of the bubble under the I bar are plotted and compared qualitatively to the similar curves obtained by continuum model. The magnetic field well under an I bar due to a trapped bubble is also calculated.
Abstract: Magnetic properties and domain structures in narrow NiFe stripes
Authors: Kryder M. H. , Ahn K. Y. , Mazzeo N. J. , Schwarzl S. , Kane S. M.
Published: February 2003

A large increase in coercivity and a small increase in the magnetoresistive effect, accompanying narrowing of stripes of Ni-Fe films and decreasing film thickness, may be due to magnetization buckling perpendicular to the stripe length. Undesirable magnetic behavior may accompany decrease in size of Ni-Fe magnetic bubble and recording head devices. (AIP)
Abstract: Evidence of a multiple q structure in CeAl2
Authors: Gurewitz E. , Shapiro S. M. , Kupferberg L. C. , Parks R. D.
Published: February 2003

Measurements on a single crystal of CeAl2 show a weak peak at the commensurate position s↘ (1/2, 1/2, 1/2) with a different temperature dependence than the incommensurate peak at ?= (1/2+α, 1/2−α, 1/2), α=0.108. This is consistent with a multiple q structure recently proposed for Nd and implies that the magnetic structure is not the simple modulation recently proposed by Barbara et al. [1]. (AIP)
Effect of a metal film on the resonance spectra of yttrium iron garnet
Authors: Dean B. A. , Wigen P. E.
Published: February 2003

Thin films of chromium and vanadium were deposited onto thin film discs of YIG and the resulting changes in the magnetic boundary conditions of the YIG were investigated using spin wave resonance. The deposition of the metal films resulted in the appearance of a surface mode in the spectra at the perpendicular field orientation for both metals. Changes in the boundary conditions with temperature were followed by measuring the relative intensities of the surface mode and the first body mode and by finding the angle of applied field at which only one mode is excited. In the Cr/YIG samples, the intensities of the even-numbered modes go through a minimum at a temperature close to the temperature of a Cr magnetic transition. This effect is due to a change in the spin-spin interaction between surface spins in Cr and YIG. By analogy, the onset of a similar change in the resonance spectra of the V/YIG samples begins at 40 K and saturates near 8.0 K, implying a magnetic transition in the surface of V.
F. M. R. characterization of exchange-coupling between a soft and a hard magnetic film
Authors: Suran G. , Sztern J. , Battarel C. P. , Morille R.
Published: February 2003

The exchange coupling mechanism of a composite film built up of a soft and a hard ferromagnet is investigated by F. M. R. measurements. The soft NiCoP layer exhibits a well defined spin wave spectra which obeys fairly well a quadratic dispersion law, with a relaxation frequency λ, which is fairly low. The hard CoP film presents a single resonance line with an extremely broad linewidth (ΔH= 2000–3000 Oe). The exchange coupling is investigated on composite film built up of the two layers by varying the thickness of the CoP layer in a systematic way, and it is shown that the linewidth ΔHn of various S. W. modes corresponding to the soft film increases as a function of CoP film thickness. The results are discussed using an exchange coupled model where the loss due to the hard film is included in the computation.
Low field microwave excitations of magnetic domain walls
Authors: Limaye P. S. , Parker A. A. , Stroud D. G. , Wigen P. E.
Published: February 2003

A theory is proposed to account for the frequency dependence of the low field absorption of microwave energy by magnetic garnet films containing a stripe domain structure. Considering only the uniaxial anisotropy field Hu and the demagnetization energy a Schrödinger like equation for the r.f. magnetization has been developed. Unbound states, for ω/γHu≳1, develop a net moment across a domain wall which couples in a non-resonant manner to an r.f. magnetic field. The frequency dependence of this coupling is calculated by box normalizing the solutions of the Schrödinger like equation. The ratio of this magnetic moment to the r.f. moment of the uniform mode is calculated and observed to be in good agreement with the experimental results.
Cubic spin model with competing bilinear and higher-degree pair interactions on a linear chain in a magnetic field
Authors: Raghavan R. , Levy P. M.
Published: February 2003

Interesting ferrimagnetic structures occur in discrete spin models with competing interactions as well as in several rare-earth compounds with the rocksalt structure. We have determined the ground states of some one-dimensional models in a magnetic field. We present exact calculations using the transfer matrix approach of the magnetization curves of the cubic spin model on a linear chain with competing nearest and next nearest neighbor bilinear as well as biquadratic interactions. The implications of the structures obtained, to models on three dimensional face centered cubic lattices, are discussed.
Magnetic excitations in ferromagnetic CeSb
Authors: Furrer A. , Hälg W. , Heer H. , Vogt O.
Published: February 2003

The magnetic excitation spectrum of ferromagnetic CeSb has been studied by neutron inelastic scattering at 4.2 K and 41.7 kOe for wave vectors along the <100≳ and <110≳ directions. Two dispersion branches have been resolved and analyzed in terms of crystal-field, bilinear and quadrupolar pair interactions. We find that the quadrupolar coupling is the dominant interaction and the bilinear exchange exhibits a strong directional anisotropy.
Exchange interactions in tetranuclear Cr3+ clusters of rhodosochloride tetrahydrate, (Cr4(OH)6(NH3)12)Cl6⋅3H2O
Authors: Furrer A. , Güdel H. U. , Hauser U.
Published: February 2003

Inelastic neutron scattering experiments have been performed on tetranuclear Cr3+ clusters embedded in the molecular compound (Cr4(OH)6(NH3)12)Cl6⋅4H2O. The observed ground-state splittings are in good agreement with the predictions of a simple Heisenberg Hamiltonian. It is shown that inclusion of biquadratic exchange terms slightly improves the data analysis.
Nuclear magnetic resonance in LaNi5
Authors: Rubinstein Mark , Swartzendruber L. J. , Bennett L. H.
Published: February 2003

Proton and La139 nuclear magnetic resonance measurements have been performed on LaNi5, LaNi5 hydrides, and LaNi5Hx with ternary additions. With ternary additions, the activation energy for proton diffusion remained unchanged, but the motionally narrowed linewidth broadened. The quadrupole interaction on the La site has been determined in LaNi5 and LaNi5Hx.
Magnetic properties of dihydrides and dideuterides of Er and Ho
Authors: Friedt J. M. , Suits B. , Shenoy G. K. , Dunlap B. D. , Westlake D. G.
Published: February 2003

The results of low-temperature Mössbauer measurements on the dihydrides and dideuterides of Er and Ho are presented in the range 1.5–10 K. The magnetic ordering temperatures observed from the onset of magnetic hyperfine splitting are in agreement with the specific heat measurements. The saturation hyperfine magnetic field at 166Er in ErH2 and ErD2 show the ground crystalline-field level to be Γ6, while it is difficult to decide between Γ6 or Γ7 as the ground state for the Er atom in HoH2 and HoD2. The measurements indicate the presence of short-range magnetic order in all the cases. Furthermore, the temperature range over which the short-range magnetic order is observed is intimately related to the stoichiometry of the hydrides or the deutrides.
ESR evidence of octahedral site occupation in ScHx:Er
Authors: Venturini E. L.
Published: February 2003

The Er3+ electron spin resonance spectrum at low temperatures in powdered Sc.9988Er.0012H1.91 contains a Γ7 doublet and associated hyperfine components with cubic site symmetry plus four additional resonances arising from two distinct transitions with axial site symmetry. The axial lines are attributed to octahedral site occupation by protons in the vicinity of some Er3+ impurities. The two axial transitions may be associated with two different types of distortions of the Γ7 wave functions or possibly a Γ8(1) quartet ground state.
EPR investigation of LaHx at varying hydrogen composition (2.30<x<2.89)
Authors: Germano D. J. , Butera R. A.
Published: February 2003

The elucidation of the electronic structure of rare earth metal hydrides, particularly lanthanum, has been of interest for many years. This paper reports the preliminary results of electron paramagnetic resonance (EPR) studies of lanthanum hydrides with hydrogen to metal atom ratios (H/M) from 2 to 3. EPR linewidths and line intensities are reported as a function of temperature and hydrogen concentration. Anamolous behavior of these parameters has been observed and is discussed.
Abstract: Quadrupolar interactions in DySb above TN
Authors: Korty F. W. , Brun T. O. , Kouvel J. S.
Published: February 2003

Results for the magnetization of DySb induced along each of the principal axes are captured in the quadrupolar coupling coefficients K and L, which vary rapidly and oppositely with temperature and whose inequality signifies a marked departure of the quadrupolar coupling from the spherically-symmetric biquadratic form. (AIP)
Hyperfine field and magnetic behavior of Heusler alloys
Authors: Stearns Mary Beth
Published: February 2003

The hyperfine fields and Curie temperatures of the Heusler alloys (X2MnZ) are analyzed and show that: (1) The s-conduction electron polarization (sCEP) is essentially independent of the X or Z element. It is also independent of the difference in the number of valence electrons between a Cd impurity, at a Z site and the Z atom it replaces. This behavior is in contradiction to the basic assumptions made in the charge perturbation models for hyperfine fields but in agreement with the assumptions of the volume overlap model. (2) The behavior of the Curie temperature shows that it is the d-conduction electron polarization not the sCEP that dominates the coupling between the magnetic Mn atoms in the ferromagnetic Heusler alloys.
Calculation of the transferred hyperfine field (volume overlap) contribution on nonmagnetic impurities in Fe and the Heusler alloys
Authors: Norbeck J. M. , Stearns Mary Beth
Published: February 2003

The transferred hyperfine fields (hff) at 4sp and 5sp solute atoms in Fe and the sp sites of the Heusler alloys have been calculated using a volume overlap model. The main difference between this and previous calculations is that the host wavefunction in the solid is represented by an orbital that is simulated from band calculations. The contributions from 2nn and 3nn atoms are also included. The calculated transferred hff values are compared to the hff contributions obtained by substracting the hff due to the host s conduction electron polarization from measured hff values. For the 4sp and 5sp impurities in Fe the calculated transferred hff contributions agree excellently with those obtained from the measured hff. The experimental data for sp impurities at the Z site of Heusler alloys is less complete than that for an Fe host, but again the calculated transferred hyperfine fields agree satisfactorily with those deduced from the measured values. Since for the Heusler alloys there are no arbitrary procedures or parameters relative to the Fe data, the agreement between the calculated and experimental values gives strong evidence in support of the volume overlap model.
193Ir and 119Sn hyperfine fields in the Heusler alloy Ir1.07Mn1.07Sn0.86
Authors: Leiper W. , Blaauw C. , Judah J. , MacKay G. R.
Published: February 2003

The magnetic hyperfine fields at the 193Ir and 119Sn sites in the Heusler alloy Ir1.07Mn1.07 Sn0.86 have been measured using Mössbauer spectroscopy. The magnitude of the 193Ir field was measured at 4.2 K as ‖H(Ir) ‖=650 kOe. This represents the first measurement of an Ir field in a Heusler alloy. The magnitude of the field is similar to that measured, at Pt sites, for both Pt and Au in the related alloy PtMnSn. The 119Sn field at 77 K was found to be ‖H(Sn) ‖=28 kOe. The experimental results for the Pt, Au and Ir sites are compared with the predictions of calculations based on charge screening models.
Abstract: Studies of selective site substitution and spin polarization in systems based on Fe3Si
Authors: Budnick J. I. , Burch T. J. , Niculescu V. , Raj K.
Published: February 2003

Transition metal elements substituted into Fe3Si were found to preferentially select one of the two inequivalent Fe sites in the Fe3Si structure, according to their location in the periodic table; a similar pattern of site occupation is observed in the Heusler alloys. Examination of the electronegativity of the transition metal impurities shows that the Fe site with 8 Fe 1nn is preferred by the less electronegative substitutions.(AIP)
Studies of ferromagnetic metals by electron spin polarized tunneling
Authors: Meservey R. , Tedrow P. M. , Kalvey V. R. , Paraskevopoulos D.
Published: February 2003

After a brief description of the technique of spin polarized tunneling into ferromagnetic metals from superconductors, experimental results to date are summarized. Measurements on polycrystalline films of 3d ferromagnetic metal elements and alloys gave positive polarization (that is, in the majority direction) in all cases. Similar results were obtained for the heavy rare earth metals. Recent tunneling measurements on single crystal Ni are described and preliminary values of the polarization are given for Ni (110) and (111) crystal faces. The results are compared to those obtained by other techniques and with theoretical predictions. Further development of the tunneling technique in single crystal ferromagnets is discussed.
Self-consistent studies of magnetic thin film Ni (001)
Authors: Wang C. S. , Freeman A. J.
Published: February 2003

Advances in experimental methods for studying surface phenomena have provided the stimulus to develop theoretical methods capable of interpreting this wealth of new information. Of particular interest have been the relative roles of bulk and surface contributions since in several important cases agreement between experiment and bulk self-consistent (SC) calculations within the local spin density functional formalism (LSDF) is lacking. We discuss our recent extension of the (LSDF) approach to the study of thin films (slabs) and the role of surface effects on magnetic properties. Results are described for Ni (001) films using our new SC numerical basis set LCAO method. Self-consistency within the superposition of overlapping spherical atomic charge density model is obtained iteratively with the atomic configuration as the adjustable parameter. Results are presented for the electronic charge densities and local density of states. The origin and role of (magnetic) surface states is discussed by comparison with results of earlier bulk calculations.
Abstract: Electronic and magnetic properties of nickel as described using experimental spin-split energy band dispersions
Authors: Eastman D. E. , Himpsel F. J. , Knapp J. A.
Published: February 2003

Angle-resolved photoemission studies of Ni (111) and Ni (100) crystals, used to determine energy-vs-momentum s- and d-band dispersions, show that ferromagnetic nickel can be described by a spin-split itinerant band model with an exchange splitting. An experimental one-electron energy band model for Ni gives a consistent description of various electronic and magnetic properties including Fermi surface radii, spin-polarized field emission and photoemission data, Bohr magneton number and optical properties. (AIP)
Abstract: Magnetic excitations in ErCo2
Authors: Koon N. C. , Das B. N. , Rhyne J. J.
Published: February 2003

We have measured the magnetic excitation spectrum of ErCo2 at 4.2 K using neutron inelastic scattering and compared the results to a Green’s function RPA theory of magnetic excitations in a ferrimagnet with crystalline electric fields; based on dynamic structure factor considerations we conclude that each of the observed scattering peaks consists of two nearly degenerate excitations, one of which corresponds to out-of-phase precession of the two rare earths in the primitive cell, while the other corresponds to in-phase precession. By comparing these results with a Green’s function RPA theory we are able to determine the Er3+ crystal field parameters as well as the Er-Co mean exchange field. (AIP)
A neutron diffraction study of Ho12Fe32O2
Authors: Melamud M. , Dariel M. P. , Shaked H.
Published: February 2003

The compound Ho12Fe32O2 is paramagnetic at room temperature, belongs to space group 1m3m and has one formula unit per unit cell. It undergoes a transition to ferrimagnetism at about 233 K. A neutron diffraction study of a polycrystalline sample of this compound was performed. The following parameters were determined and are reported: lattice constant, site parameters, transition temperature, magnetic configuration, magnetic moments of the Ho ion, Fe ion and conduction electrons. Some of these properties are also reported for the iso-structural Dy12Fe32O2.
Neutron scattering studies of the coexistence of long-range magnetic order and superconductivity in Dy1.2Mo6S8 and Tb1.2Mo6S8
Authors: Thomlinson W. , Shirane G. , Moncton D. E. , Ishikawa M. , Fischer O/.
Published: February 2003

Both Dy1.2Mo6S8 and Tb1.2Mo6S8 are superconducting below Tc=2.05 K. Neutron scattering studies show that these compounds in zero applied magnetic field develop long-range antiferromagnetic order (greater than 300 Å) at TM=0.4 K and TM=1.0 K, respectively, which does not destroy the superconducting state. Magnetization measurements at temperatures below TM suggest the development of ferromagnetic order as the applied magnetic field increases. In the case of Tb1.2Mo6S8 the neutron data show long-range ferromagnetic order developing for H?Hc2=1.9 kOe where Hc2 is the upper critical field for superconductivity. However, for Dy1.2Mo6S8 long-range ferromagnetic order begins to develop at H=200 Oe, a field much less than Hc2=1.2 kOe. As the ferromagnetic intensity increases, the antiferromagnetic intensity decreases. Between H=200 Oe and H=1.2 kOe both ferromagnetic and antiferromagnetic order occur with the sample in the superconducting state.
Neutron scattering studies of crystal field excitations in (RE)Mo6Se8
Authors: Lynn J. W. , Shelton R. N.
Published: February 2003

Neutron inelastic scattering measurements have been made to determine the crystal field levels of the rare earth ions in the ternary superconductors Tb1.2Mo6Se8, Ho1.2Mo6Se8 and ErMo6Se8. The results show that the lifting of the free-ion angular momentum degeneracies can be adequately understood on the basis of a crystalline electric field with cubic symmetry. In each case the determined ground state possesses a magnetic moment. The situation found in these selenide materials contrasts with the sulfide materials in which no crystal field excitations have been observed over a wide range of energies.
Extraordinary anisotropic magnetic behavior in cerium and actinide intermetallics
Authors: Cooper Bernard R. , Siemann Robert
Published: February 2003

Both the cerium and light actinide monopnictides with NaCl-structure show anomalous strongly anisotropic 〈100〉 magnetic ordering with similar and unusual highly anisotropic linear magnetic structures. Both theoretically and experimentally it has been shown that the presence and strength of this 〈100〉 magnetic anisotropy is in contrast with the 〈111〉 easy direction for Ce3+ in an octahedral crystal field. There are two possible origins to be considered for such anisotropy effects. One is distortional effects on the single-ion crystal field in conjunction with magnetic ordering arising from isotropic exchange, i.e. the only anisotropic interaction present is single-ion. The other possibility is the affect of anisotropic exchange, i.e. macroscopic anisotropy via a two-ion anisotropic interaction. We discuss the ways of separating out and understanding these two contributions. The weight of evidence is that both effects are significant in the cerium monopnictides; where the first effect’s being important follows from the extreme sensitivity of the crystal field to lattice displacement. On the other hand, for the actinide monopnictides, such as UAs and USb, the absence of any distortion within experimental accuracy indicates the probable dominance of anisotropic exchange effects.
Alternative modes of lattice distortion and the effects on magnetic transitions: Behavior of CeBi
Authors: Siemann Robert , Cooper Bernard R.
Published: February 2003

CeBi is a prototype material for understanding the nature of any correlation between lattice structural and magnetic structural transitions in the cerium and light actinide monopnictides of NaCl–structure. These materials show complex anisotropic magnetic behavior, often with one or more magnetic transitions below TN. At TN CeBi has type I (up-down-up-down) magnetic ordering, accompanied by the onset of a tetragonal distortion. At close to TN/2, there is a first-order transition to a IA (up-up-down-down) magnetic structure. We investigate whether the I to IA magnetic transition can be explained as being driven by a lattice structural transition from a tetragonal state (with associated type I magnetic structure) to a ++−− internal rearrangement mode (with associated type IA magnetic structure) at lower temperatures. We find that a tetragonal to ++−− lattice transition only occurs with increasing temperature. Therefore other mechanisms must be sought to explain the I to IA transition.
Elastic neutron scattering study of magnetic phase transitions in DyPO4 and HoPO4
Authors: Millhouse A. H. , Steiner M. , Dachs H.
Published: February 2003

Neutron diffraction measurements have been made on single crystals of the two metamagnets DyPO4 and HoPO4 to locate the tricritical points in these substances. In the process of the experiments an effect has been discovered which allows the accurate determination of these points. This effect is the sensitivity of the extinction of magnetic reflections to the changing domain configurations in the mixed phase below the tricritical point. Relaxation effects have been observed in the antiferromagnetic domain formation below the first order phase transition. For DyPO4 the tricritical temperature is found to be 2.07±0.05 K. In HoPO4 these extinction effects were found to be small and the deviation of the up-moment sublattice magnetization from the mean-field-theory result was used to locate the tricritical temperature at 1.0±0.1 K.
Abstract: Experimental test of extended scaling in the spin-flop system CsMnBr3⋅2D2O
Authors: Basten J. A. J. , Frikkee E. , de Jonge W. J. M.
Published: February 2003

From neutron scattering experiments on CsMnBr3⋅2D2O the staggered magnetization components M∥st  (H,T) and Mst⊥  (H,T), i.e. the order parameters of the antiferromagnetic (AF) and of the spin-flop (SF) phase, respectively, as well as the magnetic phase diagram have been obtained. (AIP)
Magnetism and superconductivity in rare-earth ternary borides
Authors: Freeman A. J. , Jarlborg T.
Published: February 2003

The observation of magnetism and superconductivity in both the ternary rare-earth rhodium borides (MRh4B4) and the Chevrel phase ternaries MxMo6S8 (with x close to 1) and most recently (i) the discovery of re-entrant magnetism accompanying a transition to a normal metallic state at T<Tsc (the superconducting transition temperature) and (ii) the coexistence of magnetism and superconductivity have generated considerable excitement as to the origin of these phenomena. We discuss the origin of magnetism and superconductivity in the MRh4B4 compounds and re-entrant magnetism in ErRh4B4 using the results of ab initio self-consistent LMTO energy band calculations. The total and separate l-decomposed contributions to the density of states (DOS) arising from the two M, eight Rh and eight B atoms per unit cell are used to estimate their various contributions to magnetic ordering (via the 4f-5d RKKY interaction) and/or superconductivity (using a Gaspari-Gyorffy model to obtain the electronic contributions to λ, the electron-phonon coupling parameter, and McMillan strong coupling theory to obtain Tsc). Comparisons are made with recent experimental results and several experimental speculations about the re-entrant magnetism state are presented including the possibility of a mixed (ferromagnetic and superconducting) state.
Neutron scattering observations on the magnetic phases of rare-earth ternary superconductors
Authors: Moncton D. E.
Published: February 2003

A number of ternary compounds become superconducting even though they contain a chemically ordered sublattice of magnetic rare-earth ions. Studies of the physical properties of these materials have revealed anomalies below Tc which have been attributed to magnetic ordering transitions. Using neutron spectrometers at the Brookhaven National Laboratory, a group of us has demonstrated that simple magnetic structures with long-range order do occur, and we have solved some of the magnetic structures of these superconductors. Specifically, we have found that in DyMo6S8 and TbMo6S8 an antiferromagnetic structure coexists with superconductivity. In two other compounds, ErRh4B4 and HoMo6S8 we have found that the development of ferromagnetism is responsible for the quenching of superconductivity. A study of the critical magnetic neutron scattering near the superconducting → ferromagnetic transitions shows the presence of fluctuations into a state with an oscillatory magnetization of wave length λ=100 Å.
Abstract: Itinerant magnetism
Authors: Matthias Bernd T.
Published: February 2003

Although, strictly, only ZrZn2 and Sc3In are intinerant ferromagnets, the phrase ’’itinerant magnetism’’ is used to describe all kinds of magnetism in metals containing well localized magnetic moments. Theoretical analysis of ZrZn2 has enabled the successful prediction of new itinerant magnets. (AIP)
Resistivity and specific heat in an induced moment ferromagnet near threshold: Pr3Tl
Authors: Bossard P. , Bakanowski S. , Crow J. E. , Mihalisin T. , Buyers W. J. L.
Published: February 2003

The temperature dependence of the specific heat and electrical resistivity has been measured for Pr3Tl. Pr3Tl is an induced moment ferromagnet for which Γ/Δ is just above the threshold value for magnetic ordering where Γ is the inter-ionic exchange and Δ is the crystalline electric field splitting of the Pr3+ ions angular momentum multiplet. Above Tc, the resistivity is substantially larger than would be expected using a single ion model. This additional contribution is attributable to the scattering from the low lying collective magnetic excitations. The temperature dependence of the resistivity and specific heat is discussed.
Magnetothermopower of dilute PdNi alloys
Authors: Cleveland J. R. , Foiles C. L.
Published: February 2003

The magnetothermopower of dilute PdNi alloys is presented and is shown to be consistent with predictions of spin-fluctuation behavior in the presence of magnetic interactions. The magnetothermopowers of PdNi and PtCo are shown to have significant differences and implications of this fact are discussed.
Magnetoresistance of silver single crystals containing rare-earth impurities
Authors: Creuzet G. , Fert A. , Spanjaard D.
Published: February 2003

We present magnetoresistance measurements on single crystals of silver containing Tb or Dy impurities together with the analysis of the contributions from quadrupole and exchange scattering.
Volume interactions between substitutional ’’sp’’ and ’’3d’’ solutes in ferromagnetic iron-based alloys
Authors: Cadeville M. C. , Biolluz A. , Maurer M. , Sanchez J. P.
Published: February 2003

Interactions between some ’’sp’’ (I) and ’’3d’’ (M) elements were previously assumed to exist in steels in order to explain their mutual segregation on the grain boundaries after tempering at low temperature. In a first part, it is shown that such volume interactions exist, and that it is possible to investigate them by measuring their effects on macroscopic (residual resistivities) and local (hyperfine fields) properties. The resistivity results are analyzed in a two band-conduction model which takes into account the pair effects and the local order (S.R.O.). Fe Ni Sb and Fe Cr Sb alloys were investigated in detail. Large Ni-Sb interaction terms are detected in the spin-down conduction band of Fe Ni Sb alloys, whereas similar terms are negligible in Fe Cr Sb alloys. The concentration dependences of 121,123Sb N.M.R. spectra confirm the resistivity results. In a second part, one establishes a correlation between the existence of large volume interactions in Fe I M alloys and the ability of I and M elements to segregate after tempering. Such a correlation is deduced from changes in 121Sb Mössbauer spectra and X-ray diffraction lines as measured in both as-quenched and tempered states. The segregated phase is identified.
Abstract: Thermal and electrical properties of Cr+1.37 at% Si
Authors: Johannesson Ch. , Åström H. U. , Rao K. V.
Published: February 2003

We have carried out simultaneous thermal conductivity, λ, and ρ studies on an alloy of Cr+1.37 at% Si in the temperature range 4–300K. (AIP)