bluuebunny/crossref_metadata_2025 huggingface dataset:
Satellite NMR in Cu doped with transition impurities
Authors: Slichter C. P.
Published: February 2003

My students and post-docs have made measurements of the conduction electron spin magnetization density, Mσ(R↘) near iron group atoms (Sc through Ni) in Cu. Mσ(R↘) produces an additional effective local field which shifts the NMR frequency of nearby shells of Cu nuclei relative to Cu nuclei far from all impurities. Resonances of nearby shells appear as weak satellites to the strong resonance of distant Cu nuclei (the main line). Mσ(R↘) at a given site is proportional through known constants to the splitting of the satellite from the main line. We have identified the shell giving rise to the satellite in many cases by use of single crystals. We find theoretically that to a good approximation Mσ(R↘) is proportional to the spin susceptibility χs of the impurity. For CuCr we find a large temperature independent χs, in contrast to CuMn and CuFe. The results lead to a picture of the electronic structure of Cr, Mn, and Fe along the lines of Schrieffer and Hirst as ions with integral numbers of d-electrons, possessing crystal field and spin-orbit couplings.
Magnetic and structural properties of ErFe3Hx hydrides
Authors: Niarchos D. , Viccaro P. J. , Dunlap B. D. , Shenoy G. K.
Published: February 2003

Pressure-composition isotherms at 20 ° C for hydrogen absorption in ErFe3 show a well-defined phase at a hydrogen concentration nH∼1.45 with equilibrium pressure∼4 torr, and a second phase with nH?2.7 having a critical temperature less than 20 ° C. For larger nH, the sloping isotherms indicate other phases with very low critical temperatures. X-ray studies show that the PuNi3 structure is retained, with increases in lattice constants as hydrogen is added. 166Er Mössbauer spectra show two crystallographically inequivalent Er sites. The corresponding magnetic hyperfine fluids decrease sharply with nH changing at different rates for the two sites. 57Fe Mössbauer spectra show complex patterns arising from the five magnetically inequivalent Fe sites.
Abstract: Kondo effect in Eu2+ systems
Authors: Lustfeld Hans
Published: February 2003

Eu2+ impurities in a metallic host combine two features which make those systems interesting: a) The indirect exchange (due to hybridization between f- and conduction electrons) is large b) Even far away from the mixed valent state the crystal field is of little importance since L=0 in Eu2+. Therefore the whole 8-fold degeneracy of the Eu2+ ground state comes into play. On the other hand the usual Kondo Hamiltonian does not apply to Eu for two reasons: The reduced matrix element to the first excited state is comparatively small and the energy difference between the first and second excited state is only 500 K. Thus the higher excited states have to be taken into account. This has been done in the calculation of the Kondo−temperature and the resistivity.
Abstract: Local moment hyperfine studies of the Kondo system PdHxFe0.3%
Authors: Brand R. A. , Georges-Gibert H. , Kovacie C.
Published: February 2003

The effect of hydrogen on the Fe giant moment in dilute Pd Fe and the resulting single moment Kondo and RKKY-interactions in Pd Hx Fe is investigated by Mössbauer hyperfine techniques in an external magnetic field. The results show that within a large range of composition within the α′ phase (hydrogen lattice liquid), Fe remains constant at about 4.2μB smaller than the 12.6 μB in dilute Pd Fe. The Kondo temperature TK is found to increase with hydrogen, as determined from the usual X=μH/k (T+ϑ) modification to the Brillouin function B1 (X) where ϑ=4.5 TK. Deviations from this modified B1 (X) have been related to the static part of the impurity interactions, and a molecular field approximation spin glass calculation is done to compensate for this. The dynamic part of the impurity interactions leads to a spin glass-type spin-spin relaxation, which produces a line broadening in magnetic field much larger for the outer Mössbauer lines and with a maximum in field at about X=1. At higher concentrations (x=0.75), the saturation HF field decreases, indicating a possible orbital component on μ (Fe), conform with certain recent calculations. Above x=0.8, new Mössbauer lines are found, indicating the phase transitions and two-phase regions α′→β and β→α″ with increasing hydrogen content. The associated changes in line position are very large, about 0.18 and 0.22 in mm/sec, in the sense of lattice expansion. The advantage of hyperfine measurements is shown by the detail of the information obtained, and especially in the possibility of separating single moment from collective effects.
Abstract: Hyperfine field at the positive muon in ferromagnets
Authors: Fiory A. T.
Published: February 2003

Positive muons are hydrogen-like impurities when implanted into metals, acting as probes of interstitial sites. This talk reviews some of the conclusions about the electronic structure around muons and interstitial magnetism drawn from measurements of the local magnetic fields in Fe, Ni, Co, Gd, Dy, dilute Fe and Ni alloys, and non-magnetic metals. Because the muon is an isolated impurity, there are no electron states associated with muon-muon interactions. The muon is present in the metal as a non-magnetic impurity, where the electron distribution resembles the H− ion. The local field on the muon arises from the Fermi-contact interaction with the local electron polarization and dipolar fields associated with the host moments, which can be treated as unperturbed point dipoles. The muon’s perturbation of the local spin density at interstitial sites is mainly an enhancement of the spin polarization of s-like electrons. In dealing with the single point-charge impurity in transition metals, the effects of local 3d orbital distortions and band filling at the Fermi level are of comparatively minor importance. The effect of muon diffusion will also be discussed. The diffusion of muons and hydrogen in Fe is characterized by similar activation energies, but the observations cannot be simply explained in terms of existing theories of phonon-assisted tunneling. One observes explicit effects of impurities, which reduce the muon jump rate at certain temperatures. Both attractive and repulsive muon-impurity potentials have been observed.
Electrical resistivity and thermal expansion of La1−xCexSn3 and CeIn3−ySny
Authors: Maury A. , Scoboria P. , Crow J. E. , Mihalisin T.
Published: February 2003

We have measured the temperature dependence of the electrical resistivity and thermal expansion of La1−xCexSn3, CeSn2In and LaSn2In from 300K to 1.5K. The CeSn3 system is interesting because a variety of previous measurements seem to suggest that the Ce ions within this system may display intermediate valence behavior. Both the thermal expansion measurements and resistivity data for these systems are presented and compared to both other known mixed valence systems and predictions for concentrated Kondo systems.
Typical spontaneous symmetry breakdown in solid state as revealed by Fe3O4
Authors: Iida S. , Mizoguchi M. , Umemura S. , Yoshida J. , Kato K. , Yanai K.
Published: February 2003

Several of our experimental results, as seen from the side of the symmetry breakdown of this most characteristic material, will be shown. X-ray study reveals that the lattice constant decreases approximately by 7×10−6 per degree from room temperature to the Verwey temperature Tv. At Tv, the cell volume increases by about 6×10−4, suggesting the presence of covalent nature in the crystal. At Tv, the crystal transforms to monoclinic. Although there is a report of another transition at about 12°K, very careful work by X-ray and NMR showed no discontinuous change in this temperature region in the accuracy up to 10−4. Detailed measurements of magnetoelectric effect were performed at 4.2°K and up to 34°K statically and dynamically. The induced electric potentials between the two planar electrodes formed parallel to a-, b-, or c-plane were observed as a function of the direction of the magnetic field in a-plane. Magnetic field cooling along [112], squeezing along [111] and electrically polarizing along a-, b-, or c-axis were simultaneously performed. We found that the electrically polarizing at and below Tv is only effective along a-axis. The crystal symmetry revealed is nearly monoclinic and may be triclinic. Again no appreciable discontinuous signal is observed near 12°K.
Abstract: Magnetic and thermal properties of YbS1.387
Authors: Taher S. M. , Ho J. C. , Gruber J. B. , Beaudry B. , Gschneidner K. A.
Published: February 2003

Magnetic and thermal properties of Ybs1.387 are presented between 4 and 300 K for the magnetic susceptibility of (χ) and between 2 and 20 K for the heat capacity (Cp). The sample appears to be paramagnetic over the temperature range studied. A plausible explanation for both the Cp and the χ data obtained can be made by considering the Yb3+(4f) ions to be found in a crystal line environment where the ground state level 2F7/2 is split by the crystalline electric field into four Kramers doublets found at 0, 6, 120, and 300 cm−1.
Magnetostriction in amorphous Ni-Co alloys
Authors: Jagieliński T.
Published: February 2003

The saturation magnetostriction λs and the volume magnetostriction δω/δH in amorphous Ni-Co alloys were measured in the temperature range from 77 K up to room temperature. The three terminal capacitance method was used. The maximum value of saturation magnetostriction was observed for (Co.8Ni.2)78Si8B14 and equals −5.1×10−6 and −6.2×10−6 at room temperature and liquid nitrogen temperature, respectively. The largest value of the volume magnetostriction constant is observed for Co78Si8 B14 composition and is equal to 3.1×10−10 Oe−1 at 300 K and 5.0×10−10 Oe−1 at 77 K.
Zero magnetostriction and low field magnetic properties of Co-Fe base amorphous alloys containing V,Nb,Ta,Cr,Mo,W,Mn or Ni
Authors: Ohnuma S. , Masumoto T.
Published: February 2003

Low-field magnetic properties of the zero magnetostrictive amorphous ribbons of (Co, Fe, M)78Si8B14 alloys (M=V,Nb,Ta,Cr,Mo,W,Mn or Ni) have been investigated. In all of these systems, the zero magnetostriction lines are located in the iron poor side less than 10 at%. The alloys containing VA and VIA group elements show highly improved low-field magnetic properties with the effective permeability exceeding 105 and the coercive force less than 2 mOe after the optimum heat treatment.
Non-magnetostrictive amorphous soft magnetic thin film material of high magnetization
Authors: Brunsch A.
Published: February 2003

Magnetically uniaxial amorphous Co79Fe6.5B14.5 films 1.5 μm in thickness were deposited by r.f. bias sputtering from a Co74Fe6B20 target onto glass and single crystal Si substrates. The saturation magnetostriction, λs, changed gradually from +0.6×10−6 to −0.4×10−6 when the d.c. bias voltage was increased from 0 to −120 V. In this bias voltage range 4πMs values from 11 up to 14 kG were measured. The influence of the Ar gas pressure on 4πMs and λs is weak. Coercivities of less than 0.05 Oe were obtained on Si substrates at bias voltages between −45 V and −90 V. The hard axis anisotropy field was decreased by hard axis field annealing at 240 °C from 12 Oe to below 3 Oe and the initial permeability increased up to 3600. The amorphous state was not affected by the annealing. The electrical resistivity of the material was 90 μΩ cm and the magneto-resistivity ratio Δρ/ρ was 0.2%. The high values of 4πMs and of the permeability, zero λs, and low Hc, combined with a high electrical resistivity suggest the application of the material in thin film magnetic devices operating at high frequencies. As for permalloy films also Co79Fe6.5B14.5 films must be protected from corrosive influences.
Magnetic properties of amorphous Fe-Si-B films prepared by Co-sputtering
Authors: Naoe M. , Yamamoto H. , Yamanaka S.
Published: February 2003

Amorphous Fe-Si-B films have been fabricated by rf tetrode co-sputtering from a composite target, which was a pure iron plate covered by chips of pure silicon and boron. SEM and EPMA studies showed that there had been neither apparent columnar texture nor compositional fluctuation in the specimen films. The typical values of saturation magnetization per gram σs, initial permeability μi, and coercive force Hc at room temperature were approximately 160 emu/g, 850, and 5 Oe, respectively. The value of μi increased remarkably with increasing the annealing temperature below the crystallization temperature (∼470 °C), while no appreciable change of σs by the annealing was detected. The annealing at about 450 °C raised μi up to approximately 3000. The as-sputtered films had a comparatively large anisotropy with easy axis perpendicular to the film plane, but the stress removal by the annealing at the temperature above 370 °C decreased Hc down to 0.6 Oe. The saturation magnetostriction λs was ∼30×10−6.
Isothermal crystallization kinetics of amorphous Fe80 (B1−xPx)20 alloys
Authors: Orehotsky J.
Published: February 2003

The kinetics of crystallizing amorphous Fe80B20, Fe80B15P5 and Fe80B10P10 alloys were monitored by isothermal electrical resistance measurements. These isothermal measurements generally displayed an initial transient where the electrical resistance increased with annealing time. The transient was followed by two apparent annealing stages where the resistance decreased with annealing time. The magnitude of the transient was dependent on the boron content and the transient appeared to be responsible for the characteristic anneal embrittlement of these alloys. X-ray diffraction results indicated that no crystallization occurred during the transient and that the alloys crystallized during the subsequent annealing stages. The kinetics of both annealing stages were found to obey the general relationship F = exp (t/τ)n, where F is the reciprocal volume fraction not crystallized, n is a coefficient and τ is a rate constant that obeys the Arrhenius relationship. The coefficient n and the activation energy Q were determined from the isothermal annealing data. For the first stage, the coefficient has a value of 1.3 for Fe80B20 while the activation energy was compositionally dependent being 44, 55, and 55 Kilocalories/mole for the Fe80B20, Fe80B15P5, and Fe80B10P10 alloys respectively. The second annealing stage had a coefficient of 0.5 for Fe80B20.
Anisotropy versus exchange in amorphous heavy-rare-earth based RE4Au alloys
Authors: Berrada A. , Durand J. , Hassanain N. , Loegel B.
Published: February 2003

We present the results of bulk magnetization measurements on splat-cooled amorphous alloys of composition RE4Au for temperatures ranging between 1.6 and 300 K and in applied field up to 45 kOe. The magnetic properties for alloys over the whole series are summarized. The problem of valency for Eu and Sm in these amorphous alloys is briefly discussed. A special emphasis is placed on non-equilibrium effects in a-Tb4Au.
Mössbauer and magnetic study of rf-sputtered Fe2O3 films
Authors: Marusak L. A. , Messier R.
Published: February 2003

We report Mössbauer and magnetic susceptibility data as a function of temperature for a thin film prepared by rf-sputtering from an Fe3O4 target in an O2-Ar atmosphere. Powder X-ray diffraction data shows very broad bands at d = 2.7, 2.0 and 1.5 Å. The magnetic susceptibility data as a function of temperature may be divided into three regions. The low temperature region (T<170 K) shows a near constant susceptibility of 1.5×10−4 emu/g. Between 170 and 225 K there is a dip in the susceptibility. For T≳225 K the susceptibility decreases with temperature in accord with the Curie Weiss law. We have estimated the Neel temperature to be 220 K from the peak in the magnetic susceptibility and the collapse of the magnetic hyperfine splitting in the Mössbauer data. While the film discussed in the present paper is amorphous, we have found that films sputtered at slightly higher power levels consist of microcrystals of γFe2 O3.
Amorphous transition metal oxide films
Authors: Heiman Neil , Kazama N. S.
Published: February 2003

We have been able to prepare amorphous oxides of Fe and Cr by sputter deposition. Magnetization measurements were made between 4.2 K and 300 K. Mössbauer spectra were obtained for the iron oxide samples in the same temperature range. Amorphous CrO2 films showed no evidence of magnetic order. For the amorphous Fe oxide films, the 4.2 K Mössbauer spectrum showed a broad symmetric six line pattern which collapsed to a doublet at T?100 K. The susceptibility of amorphous iron oxide shows a broad maximum near T=100 K and a paramagnetic moment of only 3μβ. We present arguments that this behavior cannot be described by superparamagnetism and therefore represents the intrinsic magnetic behavior of amorphous iron oxide.
Magnetic characterization of METGLAS 2826 MB ribbon
Authors: Krishnan R. , Prasad Shiva , Branska K.
Published: February 2003

Magnetization and resonance properties have been studied in the range 4.2–310K on several samples cut from METGLAS 2826 MB (Fe40Ni38Mo4B18) ribbon. Domain structure was observed by Bitter powder techniques. Perpendicular anisotropy field of the order of 300 Oe is found in the as quenched samples and it varies from sample to sample which is attributed to a non uniform distribution of stresses. Domain studies also confirm this in the sense that islands (l∼100 μm) with either maze or stripe domains are observed scattered in a random manner. Annealing at about 300° C leads to the suppression of the anisotropy. Low temperature magnetization variation is well described by M (T)  = M (O) [1−BT3/2−CT5/2] with B = 30.3×10−6 K−3/2 and C = 2.0×10−8 K−5/2. The spin wave stiffness constant D is evaluated as 110 m.e.V. Å2 and the mean square range of interaction 〈r2〉 ? 9 Å2.
Abstract: Influence of oxygen on perpendicular anisotropy in amorphous Gd-Fe and Gd-Co films
Authors: Shinoda T. , Tsunashima S. , Uchiyama S. , Fujii T.
Published: February 2003

Influence of oxygen adsorption on the perpendicular anisotropy in vacuum deposited amorphous Gd–Fe and Gd–Co films was studied. The films of typically 500 Å thickness were prepared by co-evaporation technique. As for Gd–Fe, the perpendicular anisotropy of 3×105 erg/cm3 was found in oxygen-free films but the perpendicular magnetization was not found in oxygen-adsorbed films. This difference is not only due to the increase of the magnetization resulting from the oxidation of the surface layer, but also due to the decrease of the anisotropy by the adsorption of oxygen. It was further found that Gd–Fe films of only 100 Å thickness exhibit the perpendicular magnetization if the films are not exposed to the atmosphere. For Gd–Co films, the magnetization was in-plane in as-deposited samples, but slight increase of the anisotropy was found in the sample containing oxygen during annealing at 200–300 C.
Heat capacity studies of RFe2 intermetallic compounds over the temperature region 1.5–10 K (R=Gd, Tb, Dy, Ho, Er, Tm and Lu)
Authors: Butera R. A. , Clinton T. J. , Moldovan A. G. , Sankar S. G. , Gschneidner K. A.
Published: February 2003

The heat capacities of the RFe2 intermetallic compounds (R=Gd, Tb, Dy, Ho, Er, Tm, and Lu) have been measured over the temperature region 1.5–10 K. Values for the apparent electronic heat capacity coefficients have been determined and exhibit a cusp-like behavior as the R atom is changed across the rare earth series going from Gd to Lu. The maximum is found to occur for HoFe2.
Nuclear hyperfine fields in ferromagnetic Er1−xGdxAl2 compounds
Authors: Berthier Y. , Devine R. A. B.
Published: February 2003

Nuclear magnetic resonance measurements have been made on the 167Er nucleus in ordered Er1−xGdxAl2 compounds (0?x<1). A multiple resonance pattern is observed corresponding to Er nuclei surrounded by 0,1,2,3 or 4 first nearest neighbour Gd ions. Measurements of the quadrupolar splittings for each of the observed resonances enable estimates of the associated Er〈Jz〉 values to be obtained. Comparison of the measured resonance frequency behaviour and that estimated for Jz as a function of increasing Gd concentration suggests that the molecular field does not increase as expected and that the self polarization field decreases. This behaviour may be correlated with band structure differences between ErAl2 and GdAl2.
Hyperfine magnetic field at Cd impurity site in L21 Heusler alloys Rh2MnGe and Rh2MnPb by TDPAC technique
Authors: Jha S. , Black Robert D. , Julian Glenn M. , Blue James W. , Liu David C.
Published: February 2003

The hyperfine magnetic field (hmf) at nonmagnetic cadmium impurity in L21 Heusler alloys Rh2MnGe (Tc=450 K) and Rh2MnPb (Tc=338 K) has been measured as a function of temperature by Time Differential Perturbed Angular Correlation (TDPAC) technique. Measurement utilized the 84-nsec 247-keV state (μ=−.7656 nm) in Cd-111 populated in the decay of 2.8-d In-111. Alloys were prepared by substituting for 2 atomic % of Ge or Pb by In metal which had been bombarded with 30-MeV protons. The measured hmf’s in kG at cadmium impurity, presumed to be at Ge or Pb site, are (with temperatures in parentheses) in Rh2MnGe 188±6 (77 K) and 160±3 (293 K); and in Rh2MnPb 143±2 (77 K), 114±2 (200 K), 84±2 (273 K) and 53±1 (293 K).
Hyperfine magnetic field at Cd impurity site in Clb Heusler alloys PtMnSb and NiMnSb by TDPAC technique
Authors: Julian Glenn M. , Black Robert D. , Jha S. , Blue James W. , Liu David C.
Published: February 2003

The Time Differential Perturbed Angular Correlation (TDPAC) technique has been used to measure the temperature dependence of the hyperfine magnetic field (hmf) at the site of cadmium impurity in Clb Heusler alloys PtMnSb (Tc=575 K) and NiMnSb (Tc=720 K). Serving as probe was the 84-nsec 247-keV state of Cd-111, populated in the decay of 2.8-d In-111. Alloys were prepared by substituting for 2 atomic % of Sb by In metal which had been bombarded with 30-MeV protons to produce the In-111 activity. The measured hmf’s in kG at the Cd impurity, presumed to be at the Sb site, are (with temperatures in parentheses) in PtMnSb 166±4 (77 K), 153±2 (200 K), 138±2 (293 K), 125±2 (373 K), 95±2 (473 K), and 76±2 (488 K); in NiMnSb 213±3 (77 K), 208±4 (200 K), 194±3 (293 K), 191±4 (404 K), 169±4 (519 K), and 125±4 (630 K).
Magnetic interactions in PrEu and PrGd alloys
Authors: Götz F. , Czjzek G. , Fink J. , Schmidt H. , Oestreich V. , Fulde P.
Published: February 2003

We have investigated dilute PrEu and PrGd alloys by magnetization measurements and by Mössbauer spectroscopy. At low temperatures the susceptibility of the alloys in small applied fields (1 to ∼5 kOe) is higher than that of pure Pr, but as a significant magnetic moment is induced in the Pr matrix by higher applied fields the alloy magnetization is reduced compared to that of the pure material. Both 151Eu and 155Gd Mössbauer spectra exhibit magnetic hyperfine splitting below about 10 K even in the most dilute alloys investigated (∼1 at.%). From the observed quadrupole splitting of the 155Gd Mössbauer spectra an estimate for the crystal field parameter B20 in Pr is derived. A model assuming each magnetic impurity ion to be surrounded by an antiparallel polarization cloud due to ferromagnetic spin-spin coupling can qualitatively explain the experimental results.
A cluster model for localized moments in antiferromagnetic chromium
Authors: Kelly J. R. , Moyer C. A. , Arajs Sigurds
Published: February 2003

Recent studies of the magnetic susceptibility of chromium containing small amounts (<5%) of Fe impurity indicate that in the dilute limit the major contribution to the susceptibility comes from small clusters of Fe moments interacting among themselves via a strong ferromagnetic exchange coupling. We present a calculation of the susceptibility based upon a simplified model Hamiltonian which takes account of nearest neighbor exchange coupling of the local moments as well as their coupling to the spin density wave of the Cr host. In order to obtain reasonable quantitative agreement with experiment, the model requires a strong interaction between the moments and the spin density wave. We also find that moment pairs make the most substantial contribution to the overall susceptibility.
Polarized neutron diffuse scattering measurements from a disordered Cr-Fe alloy
Authors: Kajzar F. , Parette G. , Babic B.
Published: February 2003

The results of polarized neutron diffuse scattering measurements on a disordered Cr-Fe alloy with 12 at.% of iron are reported. The measurements have been performed on a polycrystalline sample in the temperature range from 4.6 to 110 K using polarized neutron beam with wavelength of 4.25 Å and in the scattering vector range 0.2 Å−1?k?2. Å−1. The data indicate existence of a localized magnetic moment which we attribute to iron atoms in ferromagnetic clusters. The value of this moment decreases rapidly with increasing temperature. The incoherent scattering cross section is nearly constant up to 80 K and increases slightly above this temperature. The nuclear short range order is extended up to 6.3 Å and does not vary in the range of temperature in which the measurements were performed. The magnetic moment disturbance decreases with increasing temperature and is less pronounced than the nuclear short range order. The data are discussed in terms of the recently proposed model of magnetic interactions in Cr-Fe alloys proposed by Friedel and Hedman. Following this model the localized iron moment extrapolated to the saturation applied magnetic field is equal to 1.3±0.2 μB at the temperature of 4.6 K.
The extraordinary Hall effect in dilute Pd-Co alloys
Authors: Hurd C. M. , McAlister S. P. , Couture C.
Published: February 2003

We report measurements of the extraordinary Hall effect (EHE) in PdCo alloys over the range ∼2–250K in fields up to 6T. The components of the EHE arising from skew scattering and the side-jump effect are separated qualitatively and found to have negative signs, in contradiction with previous results.
Magnetic and resistive behavior of antiferromagnetic ErxLa1−xCu and ErxY1−x Cu
Authors: Boling E. , Crow J. E. , Mihalisin T.
Published: February 2003

The resistivity ρ (x,T) for the system ErxY1−xCu is shown to be consistent with a Suezaki and Mori approach to the resistivity of an antiferromagnet if the ratio of the electron energy gap resistivity term to that due to spin fluctuations is allowed to be x dependent as recently suggested by Masharev. The data is not consistent with a model that attributes the resistive behavior to Kondo scattering interrupted by an antiferromagnetic transition (this model has been used to explain ρ (x,T) for CexLa1−xAl2). Both the specific heat and magnetization show unusual behavior which may be related to the splitting of the Er3+ quartet ground state below TN.
Electrical resistivity studies of the Y1−xThxFe3 system over the temperature region of 77–300K (0<x?1)
Authors: Nelepa P. J. , Butera R. A.
Published: February 2003

The electrical resistivity of the ternary Y1−xThxFe2 system has been investigated for values of x ranging from 0.1 to 1 over the temperature region 77–300K and at 4.2K. The compounds investigated were determined to be single phase materials exhibiting the PuNi3 type structure. Values of (Δρ/ρHe) and dρ/dt) have been derived as a function of T and x. The data exhibit a decrease of (dρ/dT)x with increasing temperature for all values of x and a minima in (Δρ/ρHe)T vs. x. These results are discussed in terms of the two-band model of Mott and Jones as applied to praseodymium by Meaden and the magnetic results of Kunesh et al on the Y1−xThxFe3 system.
Electronic structure of ferromagnetic metals doped with interstitial or substitutional ’sp’ impurities
Authors: Parlebas J. C. , Demangeat C. , Cadeville M. C.
Published: February 2003

This paper summarizes our present knowledge on the electronic structure of transition metals (with a special emphasis on α-iron) doped with light interstitial (⋅⋅⋅B,C⋅⋅⋅) or substitutional (Al, Si, P⋅⋅⋅Sb⋅⋅⋅) impurities. The electronic states of the impure metal are described in a tight-binding model built from a Slater-Koster fit to first principles bands structure for the host and from a set of extra-orbitals for the impurity. Our results for interstitial or substitutional alloys are essentially characterized by ’sp’ antiresonances within the d bands; they are discussed in relation with experimental data. Also we point out several physical problems which can be solved easily within the present tight-binding model.
Conduction-electron polarization at nuclear sites due to the indirect exchange interaction
Authors: Kolk B.
Published: February 2003

An expression for the spin density at nuclear sites due to the indirect-exchange interaction is derived, using general expressions for the exchange integral and conduction-electron wavefunctions instead of the usual approximations. The expression thusly obtained is evaluated for Rn→∞ where Rn is the distance between the nuclear site and the local moment. It is shown that the behavior of the spin-density oscillations around a local moment depends on the concentration, cloc, of atoms carrying moments and that these spin-density oscillations exhibit a rather anomalous behavior for high concentrations cloc.
Theory of Kondo lattice
Authors: Jullien R. , Pfeuty P. , Bhattacharjee A. K. , Coqblin B.
Published: February 2003

In order to understand the low temperature anomalous properties of some rare-earth compounds (such as CeAl2, CeAl3, TmSe), we introduce a Kondo lattice hamiltonian in which a localized 1/2 spin per site interacts antiferromagnetically with the conduction electron spins. We investigate the ground state properties of this hamiltonian by using a real space renormalization group method. After studying a simpler one dimensional analog we study the original hamiltonian in one dimension when there is one conduction electron per site.
High-temperature series expansion for magnetic systems with single-ion anisotropy
Authors: Johnson J. W. , Wang Y. L.
Published: February 2003

An improved computational technique of the high-temperature series expansion for magnetic systems with single-ion anisotropy of arbitrary strength is presented. The method facilitates the calculation of higher-order terms in the expansion. While applications have been made to obtain susceptibility and specific heat series for spin-one ferromagnets with general single-ion anisotroy, only the general method will be shown.
Systematic generalization of the Migdal transformation
Authors: Nicoll J. F.
Published: February 2003

It is shown that the Migdal transformations should not be considered to be true lattice transformations since the same recursion relation may be derived for any lattice. A profitable point of view is to consider the various recursion transformations as approximate integrals of their common differential limit. It is then possible to construct extensions of the Migdal transformations by examining the renormalization group property and partition function invariance of a potential-moving scheme order by order in (b-1) where b is the length rescaling factor. Explicit conditions are given in a quasi-continuum approximation to 0((b−1)2).
Abstract: Dynamics of magnetic response of iron whiskers near the Curie point
Authors: Arrott A. S. , Heinrich B.
Published: February 2003

Iron whiskers are used as the core of a transformer with concentric windings to find the magnetic frequency response near the Curie temperature Tc. In this review we emphasize the dynamics at high temperatures. We discuss the magnetic viscosity and the role of magnetic fluctuations using the phenomenology of magnetic memory functions. We have introduced a new memory function from which we extract evidence for critical slowing down. The time scale of critical slowing down, which becomes as low as 10−4 sec, is given by the response time of rapidly growing correlation clusters near Tc. For temperatures slightly below Tc (Tc−.3<T<Tc−.03, the curling region) we apply equations we have developed to interpret the magnetic response of conducting soft magnetic materials. We are able to extract the intrinsic magnetic response. It is shown that in the curling region the role of the intrinsic damping is dominant and it is described by a temperature independent coefficient for the Gilbert damping. The measured loss in the curling region is higher (∼10×) than anticipated from resonance measurements. It is argued that this difference is caused by a large magnetization disorder in the curling region, contrary to resonance measurements where the disorder is small and all in the spin waves. The full paper will be submitted for publication elsewhere.
Long-time relaxation in disordered Ising chains
Authors: Dhar Deepak , Barma Mustansir
Published: February 2003

We study the long-time relaxation of magnetization in a bond-disordered, one-dimensional kinetic Ising model. We show that with a ferromagnetic two-peaked distribution of the coupling constants, the magnetization at very long times varies as exp(−λ0t−ct1/3). For low enough temperatures, there is an intermediate time regime where the magnetization varies as exp(−λ0t−bt1/2). If the distribution of bond strengths varies as a power law near some maximum value J0, we find that the magnetization at long times varies as exp(−λ0t−ct1/3(lnt)2/3).
Solitons and phasons in the Ising model with competing interactions
Authors: Bak P. , von Boehm J.
Published: February 2003

We report an analysis of the spatially modulated phase of an Ising model with competing interactions. The mean-field phase diagram, as calculated numerically, includes a large, possibly infinite, number of transitions between commensurate phases. The main features can be understood in terms of a domain wall, or ’’soliton’’ picture. Near the transitions, the solitons form a regular lattice. The elementary excitations in this lattice are the phasons. The effects of fluctuations which have been ignored in the mean field theory can be estimated by calculating the phason entropy. Only two commensurate phases, with periodicities 4 and 6 lattice units, respectively, survive at finite temperature. The remaining part of the phase diagram is a floating incommensurate phase.
Magnon contribution to the ultrasonic attenuation in planar ferromagnets
Authors: Leung K. M. , Huber D. L.
Published: February 2003

The propagation of acoustic waves in magnetic insulators is studied theoretically, first from a general point of view and then in the weak coupling limit. Both the modulation of the exchange integral and the single-ion magnetostriction are considered as coupling mechanisms between the spin and the phonon systems. At low temperatures, where the spin system can be described by non-interacting magnons, the attenuation coefficient is calculated for a planar ferromagnet. For the 1-D material CsNiF3 explicit expressions for the ultrasonic attenuation coefficient αph are computed in both zero and finite external field. αph is found to be linear in the temperature and quadratic in the phonon frequency for H=0. However, in a finite field the frequency dependence becomes linear and the temperature and field dependences are rather complicated.
On the nature of magnetic hysteresis in soft ferromagnets
Authors: Dorofeeva E. , Makarov V. , Molotilov B. , Prokoshin A.
Published: February 2003

During remagnetization along easy magnetization axis, the thermodynamical behaviour of a many-axes ferromagnet having the 180°-domain structure and non-zero magnetostriction is fully determined by the presence of two thermodynamical phases. The phase transition of the first kind is irreversible and fluctuative in nature. The nature of magnetic hysteresis in soft ferromagnets is attributed to the thermodynamical irreversibility of this phase transition.
Itinerant electron magnetism in 3d-transition metals (invited)
Authors: Cooke J. F.
Published: February 2003

Inelastic neutron scattering experiments performed on the 3-d transition metal ferromagnets have revealed striking behavior associated with the magnetic excitations found in these materials. Of particular importance is the disappearance of the spin-wave mode above a certain cut-off wave vector and the existence of spin-waves well above the Curie temperature. These phenomena are inconsistent with predictions of localized spin models but can be understood if the ’’magnetic electrons’’ are assumed to be itinerant. At low temperatures, quantitative predictions of the itinerant electron theory based on KKR energy band calculations have been found to be in excellent agreement with experiment. In addition, these calculations predicted the existence of an optical spin-wave mode in nickel which was recently observed. The extrapolation of the low temperature theory to finite temperatures, based on the concept of a temperature dependent spin splitting of the electron bands, appears to be inconsistent with experiment. More realistic attempts to develop a finite temperature theory are currently under investigation.
Fluctuating band picture of itinerant electron ferromagnetism(invited)
Authors: Prange R. E.
Published: February 2003

Renormalized band theory gives a good account of the ground state properties of iron and nickel. Standard finite temperature band theory, the Stoner theory, predicts in disagreement with experiment that the exchange splitting is proportional to Mz and that the transition temperature Tc is an order of magnitude greater than observed. We have worked out a generalization of the band theory in which fluctuations in the direction of the spin quantization are taken into account. This direction changes relatively slowly in space and time, so there is short range magnetic order, SRMO. The magnitude of the exchange splitting also fluctuates, but this is secondary, and the splitting is preserved, even well above Tc. A measure of the SRMO is given by a= (1/2) √ (∇M̂2), where ∇M̂ is the gradient of the local magnetization direction. The SRMO can be observed by neutron scattering. Spin waves with wavenumber q≳a can be set up, even in the absence of long range order above Tc. The lineshape is broadened, shifted, and skewed in a way dependent on a, and the theory is in good agreement with experiment. The value of a observed in this way above Tc is about .3Å−1 in both iron and nickel. By means of a functional integral formulation, our theory is compared with other recent approaches to this problem.
Spin wave stiffness constant in intinerant electron ferromagnetic alloys (invited)
Authors: Morkowski J.
Published: February 2003

A method of calculating the spin wave stiffness constant in itinerant electron ferromagnetic alloys is presented. The method is based on an effective magnon Hamiltonian derived in RPA and takes into account the magnon scattering contribution to the stiffness constant which is generally neglected in the existing quantitative estimates. The Hasegawa and Kanamori model of alloys is used, in the case of diluted alloys the model is generalized to take into account disorder in the hopping terms. The magnon energy is calculated by a perturbation method, contributions from single-site scattering to all orders are included. For concentrated alloys an alternative procedure based on CPA is also used. Results of calculations of the spin-wave stiffness constant for f.c.c NiFe, NiCo an b.c.c. FeNi alloys are presented.
Abstract: Soft-mode behaviour of excitations in praseodymium under pressure
Authors: McEwen K. A.
Published: February 2003

In dhcp Pr, the Pr ions (J=4) experience a crystal field which produces singlet ground states at both the locally hexagonal and locally cubic sites: the coupling between the ions on the hexagonal sites is just below the critical value for the development of a magnetically ordered phase at low temperatures. The magnetic excitations propagating on the hexagonal sites are composed of linear combinations of singlet-doublet transitions. The lowest energy mode is along TM and has a pronounced minimum at a wavevector of 0.25 Å−1. The large orbital angular momentum of Pr leads to a strong magnetoelastic coupling between the spin and lattice systems. From the field dependence of the excitation energies, Jensen1 deduced the strength of this coupling and suggested that magnetic ordering might be induced by an appropriate uniaxial stress. In a series of neutron scattering studies at the Institut Laue-Langevin, we have observed a dramatic stress dependence of the magnetic excitations2. With increasing stress along an a-direction, the lowest energy mode (longitudinal optic) exhibits a clear soft-mode behaviour. Above a critical stress, elastic satellite reflections corresponding to long-range magnetic ordering in a longitudinally modulated structure were observed. This critical stress is 800 bar (80 MPa) at 7.5 K.
Magnetic and magneto-optic properties of amorphous GdFeBi-films (invited)
Authors: Hansen P. , Urner-Wille M.
Published: February 2003

Amorphous rare-earth-transition metal alloys of composition (Gd1−xFex)1−yBiy with 0?y?0.17 have been prepared by high vaccum electron gun evaporation onto rotating glass substrates. The magnetic and magneto-optic properties have been investigated in the temperature range 4.2 K?T?TC. From the temperature dependence of the saturation magnetization the compensation temperature is found to decrease strongly with increasing y (Tcomp=0 for x=0.74, y=0.1) while the Curie temperature and the temperature for crystallization are much less affected. The magneto-optic Faraday and Kerr rotation display a considerable increase with increasing Bi-content. The temperature behavior can be interpreted in terms of the mean field analysis indicating a pronounced influence of the bismuth on the iron moment and the exchange constants.
Optical spectrum of nickel: Anomalous temperature dependence around TC
Authors: Stoll M. Ph. , Jung C.
Published: February 2003

The optical constants of nickel are found to vary with temperature. Most of the temperature dependence is carried by a Drude-like term, with a temperature dependent relaxation time τ−1(T) =τ−10+bT2. The interband absorption itself has an anomalous behaviour in that it first increases with T, then over ΔT?100° around TC, falls down rapidly by same amount. The interband polarization ε1 shows a small singularity at TC. There is presently no straightforward explanation for these phenomena. Structures in the interband absorption spectrum, above 0.8 eV, are found to correlate well with a recent photoemission deduced band model, and particularly confirm the smaller (∼3.5 eV) width of the d band. Simultaneously a value of 0.1 eV for the spin-orbit parameter, and an estimate (0.4 eV) for the exchange splitting of L31, are obtained.
Bound hole pairs in Ni: Evidence from photoemission
Authors: Penn David R.
Published: February 2003

I show that the Ni d-band density of states contains a peak due to excitations of bound hole pairs. The density of states is observed directly in photoemission experiments which show a satellite peak below the bottom of the d bands.
Numerical study of the square Ising frustration model
Authors: Vannimenus J. , De Sèze L.
Published: February 2003

Ground state correlations in the Ising model with random ± J bonds are investigated on a square lattice, as a function of the concentration of negative bonds. By comparing all the ground-states of (18×18) samples, we study the size distribution of packets of solitary spins. Large packets, containing more than half the spins, are observed in most samples, even at maximum bond disorder. This finding implies a remarkable rigidity of the random frustrated system at zero temperature.
Frustration effects in 2D regular Ising models
Authors: André G. , Bidaux R. , Carton J-P. , Conte R. , de Seze L.
Published: February 2003

Exact results are obtained for two-dimensional Ising models in which periodic conflicting interactions induce frustration effects. A brief review of the remarkable thermodynamic and magnetic properties of these models is presented. For specific choices of the interactions, the main features predicted are: (1) The existence of systems with a highly degenerate level of lowest energy, leading to a residual 0K entropy per spin. (2) According to the distribution of interactions, the existence of a residual 0K entropy is not an impediment to the onset of long range order at finite temperatures. However, if such an order takes place, the corresponding order parameter may not be saturated at 0K, and the associated susceptibility will diverge at 0K as well as at the transition temperatures. (3) Long range spin correlations 〈S(O⃗)S(R⃗) 〉 at 0K averaged over all ground states are studied in one of the models (which includes the ’’odd model’’) for simple crystallographic directions of R⃗. They are shown to decrease as f (R⃗) ⋅R−1/2 where f (R⃗) is an oscillatory factor, proper to each R⃗ direction, which results in marked anisotropy effects.
A magnetization study of amorphous MnSi
Authors: Cochrane R. W. , Strom-Olsen J. O. , Rebouillat J. P.
Published: February 2003

We report magnetization measurements on sputter deposited amorphous MnSi. Above 100 K the susceptibility follows a Curie Weiss law, but deviates considerably from it at lower temperatures. At 21 K the alloy becomes a spin-glass. Comparison with the properties of crystalline MnSi suggests that the two systems have very similar interactions and that amorphous MnSi, like crystalline MnSi, is probably itinerant.
Spin-glass properties of a concentrated system with ferromagnetic and antiferromagnetic interactions
Authors: Tholence J. L. , Holtzberg F. , McGuire T. R. , von Molnar S. , Tournier R.
Published: February 2003

The Eu1−xGdxS system goes from ferromagnetism for small x to antiferromagnetism for large x[1]. We have studied the specific heat and the magnetic properties of that system in the concentration range where the Curie-Weiss temperature, ϑ, changes sign. Both measurements clearly indicate a spin-glass freezing for x ∼ 0.5 and a mixed state for x ≳ 0.6. Ferromagnetic clusters have been observed in both the spin-glass and in the mixed regimes.
Thermoremanent magnetization and blocking temperatures in Ni3Mn
Authors: Goldfarb R. B. , Patton C. E.
Published: February 2003

Initial susceptibility and thermoremanent magnetization measurements have been made on atomically disordered and weakly ordered Ni3Mn. The blocking of superparamagnetic clusters yields a peak in initial susceptibility near 110 K. Ferromagnetic clusters with Curie temperatures near 265 K cause a break in the susceptibility vs. temperature curves at 265 K. Exchange anisotropy effects appear below 35 K.
Transverse magnetoresistance in AgMn in the spin glass regime
Authors: Nigam A. K. , Ray R. K. , Srinivasan T. M. , Majumdar A. K.
Published: February 2003

Transverse magnetoresistance (TMR) have been measured in two AgMn (1.1 and 5.4 at.%) as well as in one AuFe (6.6 at.%) alloys between 1.5 and 77 K. There is a low-field positive TMR below the spin-freezing temperature To decreasing sharply with temperature. The negative TMR at higher fields is almost temperature-independent below To. Above To, the magnitude of the negative one increases with field and gradually decreases with temperature. Freshly annealed samples show a definite reduction of the magnitude of the negative TMR for the concentrated alloys. There is no change in the case of the dilute AgMn. The above common features will be qualitatively explained in terms of thermal and magnetic unlocking of spins, magnetic ordering and the spin-flip scattering.