bluuebunny/crossref_metadata_2025 huggingface dataset:
An easy method to determine carrier-capture cross sections: Application to GaAs
Authors: Stievenard D. , Bourgoin J. C. , Lannoo M.
Published: February 2003

A new technique of measuring capture cross sections is presented, based on a simplified analysis of the kinetics of filling of the traps in the slow regime of filling. The main interest of this technique is that it uses large impulsions, easy to apply on any sample, contrary to previous work which needed very short impulsions. A simplified theory is also developed to extract capture cross sections from the experimental data. The results are compared with those obtained by other techniques on the trap E3, created by irradiation of electrons in n-type GaAs, showing very good agreement.
Modulational instability of helicon waves in a magnetoactive semiconductor n-InSb
Authors: Salimullah Md. , Ferdous Tahmina
Published: February 2003

In this paper we have studied the modulational instability of a beam of high amplitude helicon wave in a magnetoactive piezoelectric semiconductor. The nonlinear response of electrons in the semiconductor plasma has been found by following the fluid model of homogeneous plasmas. The low frequency nonlinearity has been taken through the ponderomotive force on electrons, whereas the nonlinearity in the scattered helicon waves arises through the nolinear current densities of electrons. For typical plasma parameters in n-type indium antimonide and for a considerable power density (∼20 kW cm−2) of the incident helicon beam, the growth rate of the modulational instability is quite high (∼107 rad s−1).
Influence of hydrogen on electronic transport in dc triode sputtered amorphous silicon
Authors: Longeaud Ch. , Baixeras J. , Arene E. , Mencaraglia D.
Published: February 2003

The electron drift mobility μn in dc triode sputtered amorphous hydrogenated silicon (a-Si:H) has been measured using a time of flight experiment. Moreover the product of the mobility by the lifetime (μn τn) has been determined from the steady state photoconductivity. Thus it has been possible to study the influence of hydrogen on both mobility and lifetime. The results indicate that the incorporation of hydrogen in a-Si:H greatly increases the electron lifetime but has little effect on the trap limited mobility. This behavior can be explained in the following way: the H incorporation reduces the number of deep lying localized states, corresponding to dangling bonds and acting as recombination centers, but has little influence on the states in the conduction band tail, which control the trap limited mobility.
Electromigration in indium thin films
Authors: Reddy K. V. , Prasad J. J. B.
Published: February 2003

Neutron activation and tracer scanning technique is employed to estimate the electromigration shift in indium thin films. The electromigration effective charge number Z* is determined as a function of current density at 399 K and it was noticed that 1.40×104 A/cm2 is the threshold current density at this temperature. The variation of Z* with temperature is studied in the temperature range 352–418 K. The value of Z* is negative in the entire temperature range studied. The magnitude of Z* decreases initially, goes to a minimum at 384 K and increases rapidly above this temperature. Autoradiographs of some of the samples are also given which show the electromigration shift very clearly. The initial decrease in the magnitude of Z* is due to the increase of lattice scattering of electrons and the increase close to the melting point is attributed to the grain boundary melting of the material.
Electron spin resonance study of defects in Si-SiO2 structures induced by As+ ion implantation
Authors: Stesmans A. , Braet J. , Witters J. , DeKeersmaecker R. F.
Published: February 2003

Results are presented of an electron spin resonance (ESR) study carried out at cryogenic temperatures (4.2 K≲T≲35 K) at X- and K-band frequencies of spin-active defect centers created by ion implantation of 1014 As+ cm−2 at 60 or 80 keV into the SiO2 layer of Si-SiO2 structures (dSiO2=104–130 nm). Observations were made on single-crystal boron doped (001) Si wafers of resistivities ρ300 K=0.23 and 22 Ω cm, which had been thermally oxidized. In general, three well-distinguished centers are observed; two signals, which originate from centers residing in the SiO2 layer, showed typical ‘‘glass’’ pattern line shapes. The first is definitely proven to be the E′ center, which constitutes the first clear experimental evidence of the E′ center in ion-implanted Si/SiO2 structures. The second signal is shown to correspond very nearly with the ‘‘wet’’ oxygen-related hole center (OHC) with zero crossing of the derivative spectrum dP/dB given by ga=2.0095. A third previously unreported anisotropic center located at the Si/SiO2 interface appeared after annealing, with g=1.9998±0.0001 (for magnetic field B∥ [001]) and linewidths ΔBptp=0.42±0.02 and 0.49±0.04 mT at 9.0 and 20.9 GHz, respectively. The influence of annealing in dry N2 at 1000 °C and the temperature dependence of the ESR signals are discussed.
Identification of impurities in GaAs by the magneto-optical photoluminescent spectroscopy technique
Authors: Reynolds D. C. , Colter P. C. , Litton C. W. , Smith E. B.
Published: February 2003

Three residual donors (Si, S, Ge) and three residual acceptors (Ge, C, Zn) have been identified simultaneously in a p-type GaAs crystal. The donors were identified by the magneto-optical photoluminescent spectroscopy technique. The Si donor has also been identified by the same technique in a relatively heavily doped sample (∼5×1015 cm−3) of GaAs. A residual S donor has also been identified in still another Si-doped sample. These results demonstrate the versatility of the photoluminescence technique for materials characterization.
Nitrogen related defect centers in zinc selenide
Authors: Leigh W. B. , Wessels B. W.
Published: February 2003

Acceptor levels associated with nitrogen in vapor-grown zinc selenide have been observed with optically excited transient capacitance spectroscopy. Three hole traps with energy levels of Ev +0.085, Ev +0.10, and Ev +0.16 eV, respectively, were detected in the deliberately nitrogen doped material. An electron trap at Ec −0.35 eV whose concentration increased upon nitrogen doping was also detected. Total concentrations of the shallow hole levels were as high as 1×1016 cm−3 indicating the potential of nitrogen as a p-type dopant for zinc selenide p-n junction fabrication.
Fabrication of green-emitting monolithic GaP light-emitting diode displays by laser-induced ablation and ion implantation
Authors: Krimmel E. F. , Lutsch A. G. K. , Hoffmann L. , Weyrich C.
Published: February 2003

A novel and simple method for the fabrication of green-emitting monolithic GaP:N displays comprises pulsed ruby laser irradiation-induced, self-aligned ablation combined with self-aligned ion implantation. The different fabrication steps are described. With this technology, displays with reduced optical crosstalk and hence very high contrast in the range of 1:100 are obtained.
Irreversibility in Ising and Heisenberg spin glasses (invited)
Authors: Grest Gary S. , Soukoulis C. M. , Levin K.
Published: February 2003

Spin glasses are rather unique systems which show simultaneously apparent phase transitions as well as metastable or glassy behavior. The existence of irreversible behavior appears to be intimately connected with the phase transition. Here, we will review experiments which show irreversible phenomena and will deduce from the data a simple heuristic picture of the free energy surface F[mi], where mi is the thermally averaged spin at site i. The picture that follows from this analysis is then made more rigorous within a calculational scheme, in which, for large-size systems, we numerically compute the evolution of minima of mean field models for F[mi] as the magnetic field H and temperature T are changed. For Ising spins, magnetic hysteresis, field-cooled, zero-field-cooled, and remanent magnetizations are computed and found to be in good qualitative agreement with experiment. For Heisenberg spins, we find no irreversibility unless anisotropy is present. We discuss the re-entrant ferromagnet–spin glass transition as well as the effects of various kinds of anisotropy, on vector spin glasses. The overall good qualitative agreement between theory and experiment lends support to our hypothesis that, on intermediate time scales, the behavior of spin glasses reflects the properties of the free energy surface: that irreversibility occurs when minima of F are destroyed with changing H or T.
Mean-free-path effects in Cu3Au(Mn) spin glass
Authors: Thompson J. R. , Ellis J. T. , Thomson J. O.
Published: February 2003

A SQUID-based investigation of the static magnetization of interacting Mn ions in Cu3Au has been undertaken in order to ascertain the influence of reduced mean free path (mfp) on the indirect RKKY interaction in the spin glass. Cu3Au is a noble metal, order-disorder alloy system, in which the electrical conductivity and electronic mfp l are reduced substantially by disordering. This attenuates the indirect interaction between Mn ions for 〈r〉≲l, where 〈r〉 is their average separation. We find the reduction is clearly evident in the spin glass properties of the dilute alloys. Polycrystalline samples of Cu3Au containing 16, 58, and 266 at. ppm Mn were arc melted, ordered (disordered) by heat treatment, and x-rayed for verification of structure. The field-cooled dc magnetization M(T) was measured as a function of temperature T to 0.012 K in applied fields up to 600 Oe. Disordering produced large decreases in the spin interaction temperature Ti and increases in α, defined by the empirical relation for the low-temperature magnetization M(T)=M(0)[1−αT3/2]. Introduction of an exponential damping factor accounts satisfactorily for mean-free-path effects in the dilute alloys.
The isothermal remanence (IRM) and the thermoremanence (TRM) of spin glasses
Authors: Aharoni A. , Wohlfarth E. P.
Published: February 2003

The magnetic field dependence of the IRM and TRM of spin glasses is interpreted on the basis of Néel’s cluster model. Particular attention is paid to the commonly observed TRM maximum. The experimental results are well explained by modeling the observation of Beck that it takes a finite time for the magnetic field to be switched off. The cluster volumes are taken to be distributed according to a Gaussian probability.
Region of validity of scaling behavior for a finite spin Ising model in the ferromagnetic regime
Authors: Roshko R. M. , Williams Gwyn
Published: February 2003

The results of a finite spin Ising model calculation, in which the effects of disorder are introduced through various moments of the effective field distribution, are presented for the case of a ferromagnetic ground state. These calculations confirm the existence of critical peaks in the susceptibility above TC, the analysis of which can be used to extract the critical indices γ, β, and δ. The systematic behavior of the simulated data reproduces that observed experimentally in the PdMn system, and indicates that the region of validity of scaling behavior is confined to a progressively smaller region of the (m, h, t) diagram as one moves away from the purely ferromagnetic limit.
Magnetic viscosity in a C
uMn spin glass as evidence of strong domain wall pinning
Authors: Gaunt P.
Published: February 2003

The magnetic viscosity parameter of a 0.243% CuMn spin glass rises to a maximum value in an applied field Hm below the glass temperature. Hm increases as the temperature is lowered. We find that H1/2m is a linear function of T2/3. Hm is interpreted as the coercive force of the most prevalent fraction of a magnetically ordered portion containing domain walls and showing strong pinning effects. The magnitude of this most probable fraction of the distribution increases by a factor of 208 on cooling from 3.26 to 1.36 K.
Domain observation in ferromagnetic and reentrant EuxSr1−xS
Authors: Dillon J. F. , Albiston S. D. , Batlogg B. , Schreiber H. , Maletta H.
Published: February 2003

Optical microscope observations have been made of magnetic domains in single crystals of EuxSr1−xS with the nominal value of x=1.0, 0.70, 0.54. No magnetization structure was seen for several lower values of x. Susceptibility measurements in the Curie–Weiss law regime and electron microprobe measurements were used to characterize the individual samples. The abrupt onset of visible magnetization structure on cooling provides a sensitive measure of TC. In striking contrast, on further cooling of a reentrant composition the contrast fades very slowly. Thus the change from ferromagnet to spin glass is spread over several tenths of a degree Kelvin. All of the crystals contain thin plate-like inclusions of a second Eu rich phase which represents less than about 0.1% of the volume. The observed domains differ considerably with Eu concentration. The salient characteristics may be summarized for nominal x=1.0: polygonal domains with M largely normal to the (100) sample plane; typical dimensions, 3–25 μm; x=0.7: magnetization lies in the plane with large prismatic closure patterns around each inclusion flake; domains are seen by magnetic birefringence contrast; x=0.54: extremely fine structure overall. Where organized by imperfections it is much coarser and more readily visible.
Critical behavior and magnetic ordering in amorphous TbFe2
Authors: Rhyne J. J. , Glinka C. J.
Published: February 2003

The zero field small angle neutron scattering from amorphous TbFe2 above the magnetization-determined TC =409 K shows a conventional Lorentzian line shape with a spin correlation length which increases to only about 135 Å at and just below TC. There is only a weak indication of a cusp in the scattering in the vicinity of TC, and below TC the scattering continues to increase with decreasing temperature, finally saturating below about 40 K. The Lorentzian behavior observed above TC gradually evolves into a power law dependence I∝Q−n with n≊3 for temperatures below about 300 K. This subcritical scattering can also be approximately represented by the sum of Lorentzian (L) and Lorentzian-squared (L2) terms as suggested for random anisotropy field systems and yields a correlation length of 122 Å at 295 K. On application of a field in the range 2–12 kG at 295 K, the overall scattering at low Q is sharply suppressed indicating an increase in the ferromagnetic component with field. The residual magnetic scattering exhibits a prolate distortion of the intensity with respect to the direction of H which demonstrates that the remaining spin clusters do not exhibit a ferromagnetic response.
Anomalous behavior of the spin dynamics in a Ni-Mn ‘‘reentrant’’ alloy
Authors: Hennion B. , Hennion M. , Hippert F. , Murani A. P.
Published: February 2003

Neutron-scattering measurements in a ‘‘reentrant’’ Ni78.4Mn21.6 alloy reveal well-resolved spin waves at all temperatures below Tc (330 K) including below the downturn of the ac susceptibility (40 K). Below 120 K, spin waves coexist with an intense quasielastic scattering which suggests the coexistence of ferromagnetism and spin glass character down to T=0 K. However, below 160 K the spin dynamics shows an anomalous behavior marked by an increase of the stiffness constant. An applied magnetic field, high enough to saturate the magnetization, reduces the intensity of the quasielastic peak but does not suppress it.
Investigation of the ferromagnetic-spin glass transition in a-(Fe77Cr23)75P16B6Al3
Authors: Wicksted J. P. , Shapiro S. M. , Chen H. S.
Published: February 2003

Elastic and inelastic neutron scattering studies were performed on the amorphous alloy (Fe77Cr23)75P16B6Al3. These measurements were conducted over a temperature range from 1.8 K to room temperature. The elastic scattering results obtained at Q=0.025 Å−1 indicated a Curie temperature ∼184 K in addition to a ferromagnetic-spin glass transition below 15 K. These values are consistent with the phase diagram construction resulting from the magnetization and ac susceptibility measurements of Yeshurun et al. Inelastic neutron scattering measurements resulted in well-defined spin waves being observed in the ferromagnetic phase. For the small Q range studied (0.05–0.1 Å−1), the spin wave energies followed a quadratic dispersion. As the temperature was lowered towards the spin glass regime, the spin wave energies decreased indicating a softening of the magnetic stiffness constant. Below 10 K, no well-defined spin wave excitations were present; however, a quasielastic peak, which increased slightly as the temperature was lowered, was observed.
Metallurgical explanation of ‘‘double magnetic transitions’’ and allied phenomena in AuFe alloys
Authors: Borg R. J. , Violet C. E.
Published: February 2003

Evidence for two magnetic ordering temperatures in AuFe alloys (0.1<XFe<0.28) is given by ac and static susceptibility measurements and Mössbauer experiments. These data have given rise to a variety of qualitative to semiquantitative theories based upon fluctuations in the random distribution of Fe atoms. Our explanation of the two ordering temperatures is based upon the precipitation of metastable Fe-enriched regions which arise via a decomposition and which magnetically couple to the spin-glass matrix. The high temperature transition denotes the onset of ferromagnetic order within the ‘‘precipitate’’ whose field is then coupled to the paramagnetic matrix. When the temperature of the system is decreased below the spin-glass ordering temperature, the apparent high temperature ferromagnetic character is destroyed, attesting to the dominance of the random spin-glass structure and the strength of the coupling between the two phases. Hence, it is the temperature dependence of the coupling between distinguishable ‘‘phases,’’ as well as the nature of the magnetic order, which produces the double transition.
Muon spin relaxation in spin glass P
dMn
Authors: Heffner R. H. , Leon M. , Schillaci M. E. , Dodds S. A. , Gist G. A. , MacLaughlin D. E. , Mydosh J. A. , Nieuwenhuys G. J.
Published: February 2003

Muon spin relaxation (μSR) rates have been measured in transverse, longitudinal, and zero applied fields for the spin glass PdMn (7 at. %), and are compared with a previous study of the disordered ferromagnet PdMn (2 at. %). The calculated paramagnetic state transverse field relaxation rate for noninteracting spins is much larger than the observed rate in spin glass PdMn, but is in good agreement with ferromagnetic PdMn. The zero field relaxation rate shows a sharp cusp at Tg=5 K. An applied longitudinal field of 5 kG is insufficient to suppress this cusp in spin glass PdMn, but will suppress a similar cusp in ferromagnetic PdMn. Below Tg, a distribution of quasistatic local fields is observed in zero field, which has the same temperature dependence for both samples. Comparisons with model calculations are discussed.
Experimental evidence for magnetic two level systems in spin glasses (invited)
Authors: Wassermann E. F. , Herlach D. M.
Published: February 2003

We report about low temperature measurements of susceptibility, magnetization, and time dependence of the thermoremanent magnetization on amorphous magnetic alloys (PdCuSi) with transition metals Mn, Fe, and Co in a concentration of x=5 to 20 at. %. Alloys with low concentrations show single peak spin-glass behavior. The more concentrated samples show magnetic double transitions, with an upper transition at Tc into a ferromagnetic state, followed by a lower transition at Tg into a state which has a spin- or cluster-glass character. Evidence for this comes from the onset of irreversibility and time dependence of the remanence, features which are absent above Tg. The results can be interpreted by thermal relaxation of cluster moments over anisotropy barriers, or in an equivalent picture by the existence of magnetic two-level systems (MTLS). Direct evidence for the existence of MTLS comes from investigations of the phonon thermal conductivity κPh(T) studied as a function of temperature and magnetic field. Enhancement of κPh(T) in a field of 5 T is found for Fe and Co, yet only in the cluster-glass range T<Tg. We conclude that the phonons, coupled via a 1-s coupling to the cluster moments, scatter inelastically from the MTLS; i.e., the phonons excite the magnetic clusters over their anisotropy barriers. The results are discussed within the framework of a phenomenological model describing the low temperature properties of spin glasses in terms of a distribution of asymmetrical double well potentials.
Mechanism for enhanced unidirectional spin-glass behavior in layered Mn-Ni/Co structures
Authors: Stearns Mary Beth
Published: February 2003

Magnetization measurements on compositionally modulated structures (CMS) consisting of alternating layers of Mn and Co or Ni show spin-glass behavior for CMS of equal layer thicknesses of less than 25 Å for Ni and 15 Å for Co. Some of the Mn-Ni CMS are found to have large uniaxial and unidirectional anisotropy fields of the order of 1500 Oe. We propose a mechanism for the origin of these anisotropy fields. The d conduction electron polarization (dCEP) is known to be responsible for the antiferromagnetic coupling between the localized moments on adjacent Mn atoms and the ferromagnetic coupling between Mn-Ni or Co and Ni-Ni or Co-Co pairs. The character (AF or FM) of the dCEP coupling is determined by the density of itinerant d electrons in the vicinity of the atoms. Since Mn, Ni, and Co have different d conduction electron densities in their vicinity, any grouping of three or more atoms containing both Mn and Ni/Co atoms will have an anisotropic unidirectional dCEP distribution associated with it. Thus the anisotropic character of the dCEP in an inhomogeneous mixture of Mn with Ni or Co provides a mechanism for producing unidirectional spin-glass behavior. From simple geometric considerations the layering of Mn and Co/Ni intrinsically causes preferred directions for the anisotropy of the dCEP which, as observed, can give rise to large unidirectional fields in the CMS. This same mechanism should also be operative in any random alloy system although it will be enhanced in the layered structures of CMS films.
Spin-glass-like freezing in disordered MnPd3 and CrPd3 alloys
Authors: Rashid M. H. , Sellmyer D. J.
Published: February 2003

We report studies of dc and ac susceptibility and high-field magnetization on disordered samples of MnPd3 and CrPd3. Both samples undergo spin-glass-like transitions, as is evident from susceptibility peaks at 45 and 37 K, respectively. The effective paramagnetic moments deduced from Curie–Weiss fits of the susceptibility in the paramagnetic region are 0.38μB/Mn and 0.4μB/Cr. Both materials show saturation effects at high applied fields and a flat χ(T) below the spin-freezing temperature in the field-cooled state. The data are discussed in terms of a cluster-glass model with local antiferromagnetic interactions.
Crystallization and hyperfine fields in Fe-Hf based amorphous alloys
Authors: Dunlap R. A. , Jones D. F. , Stroink G.
Published: February 2003

The magnetic properties and crystallization have been investigated in the amorphous ferromagnets Fe80−xHfxB12Si5Al3 (0≤x≤9). The Fe hyperfine field and Fe magnetic moment were found to be 285 kOe and 1.51 μB, respectively, in Fe80B12Si5Al3. These quantities were found to decrease with increasing x by 9 kOe per atomic percent and 0.063 μB per atomic percent, respectively. The ratio of the Fe field to the Fe moment, however, was found to be essentially independent of x at 180 kOe/μB. A thermal analysis measurement of the alloy Fe80B12Si5Al3 showed two crystallization peaks: one at 730 and the other at 804 K. Both of these increase in temperature as Hf is added to the system. For x≥3, additional crystallization process peaks were observed which are presumably due to the crystallization of Fe–Hf phases.
Onset of magnetism in iron-chromium glasses
Authors: Boliang Yu , Coey J. M. D. , Olivier M. , Ström-Olsen J. O.
Published: February 2003

Mössbauer spectra at 4.2 K of (Fex Cr100−x) By metallic glasses with 50≤x≤100 and y≂20 have been analyzed to yield hyperfine field distributions. The average hyperfine field is roughly proportional to the magnetization per iron atom and it can be fitted to the expression 〈Bhf〉 =aμFe +bμ̄ using the same coefficients (a=6 T/μB, b=9 T/μB) as for crystalline Fex Cr100−x. The region of onset of ferromagnetism around x=60 coincides with the inhomogeneous appearance of a moment on the iron, magnetic and nonmagnetic iron atoms coexisting at 4.2 K up to x=80. The variation in Curie temperature for 60≤x≤100 is mainly due to the variation of the iron moment. Chromium neighbors are much more effective in reducing the magnitude of the iron moment in glasses than in the bcc crystals, and some possible reasons for this are discussed.
Low magnetostrictive amorphous Fe-Nb-Si-B alloys
Authors: Yoshino H. , Inomata K. , Hasegawa M. , Kobayashi T. , Sawa T.
Published: February 2003

Magnetostriction and magnetic core loss at high frequency up to 50 kHz were investigated together with saturation magnetization, Curie temperature, and crystallization temperature for amorphous (Fe1−xNbx)83Si5B12 alloys. Magnetostriction decreases with Nb content, and becomes 1×10−6 for x=0.115. Magnetostriction was shown not to be proportional to the square of saturation magnetization unlike many Fe-based amorphous alloys. Iron loss at high frequency was measured on the core before and after resin molding. Iron loss increase due to resin molding was reduced as magnetostriction decreases. The incremental rate of the loss due to resin molding was increased as frequency decreases.
Effects of neutron irradiation on magnetic permeability of amorphous and crystalline magnetic alloys
Authors: Brown R. D. , Cost J. R. , Stanley J. T.
Published: February 2003

In order to compare the radiation resistance of amorphous and crystalline magnetic alloys, samples of commercial high-permeability alloys were irradiated with high-energy neutrons near the beam stop of LAMPF. Both crystalline and amorphous alloys showed a decrease of permeability with increasing fluence. Samples prepared from Permalloy (crystalline) and the amorphous alloys Metglas 2605S-3 and 2705M were tested. The permeability of the Metglas 2605S-3 sample showed the slowest rate of decrease, being at least a factor of ten slower than for the Permalloy. The permeability decrease as a function of fluence for Metglas 2605S-3 appears to occur in two stages. It is proposed that the first stage is due to directional short-range ordering that occurs at an enhanced rate due to the excess point defects produced by the irradiation. The second stage is thought to be caused by pinning of domain walls by defect clusters produced by the collision cascade.
Field induced anisotropy in amorphous Co100−xTix thin films
Authors: Suran G. , Ounadjela K. , Sztern J. , Sella C.
Published: February 2003

Co100−x Tix amorphous thin films were deposited by rf sputtering in the presence of a magnetic field applied parallel to the film plane. The deposition parameters were determined in order to obtain films with negligible perpendicular anisotropy Kp, small coercive field Hc, and a well-defined in plane uniaxial anisotropy Ku. When the rf input power Ip is higher than a critical value, Kp is developed via a columnar structure, and for Ar pressure PAr higher than 3×10−3 Torr, Hc shows a large increases. Samples deposited under optimal conditions (Ip =100 W, PAr =3×10−3 Torr) present soft ferromagnetic properties and a large value of Ku, with 1.2×104<Ku <2.5×104 erg/cm3 for 7.5<x<16, Ku decreasing with decreasing Co content. The results suggest that Ku should be induced during the deposition process if one wants to obtain a large field induced anisotropy.
Amorphicity, heterogeneity, and the Arrott plots (abstract)
Authors: Aharoni Amikam
Published: February 2003

The Arrott plots make a very powerful and important tool for an accurate determination of the Curie point and of the ‘‘critical’’ exponents near that point. But after being used successfully for almost two decades, the method’s original purpose has been somehow forgotten, and some attempts have recently been made to use it out of its natural region of applicability. Like every tool, this one also has its limitations, and leads to the wrong results when they are ignored. In particular, these plots are based on an equation of state for the saturation magnetization, and cannot reveal any meaningful information for magnetic fields which are too low to saturate the sample. There is thus no point in using the Arrott plots (as some do) to look for the infinite susceptibility without ferromagnetism, predicted for amorphous materials in low fields by a theory which neglects everything that really happens in low fields. On the other hand, too high fields also distort the plots which are based on a first-order expansion. These, and other limitations will be discussed, and an analysis of their significance will be given. A conclusion of this analysis is that available experimental data do not necessarily indicate a sharp transition at a well defined Curie point in amorphous ferromagnets, as is normally assumed. An equally justified interpretation is that this is only due to an inappropriate extrapolation of the Arrott plots. Therefore, amorphous materials might be just a heterogeneous system of ferromagnets (e.g., the mixture of clusters assumed in some theories), with a region of an ill-defined transition from ferromagnetism to paramagnetism. For high degree of short-range order, the ‘‘smearing’’ of the transition region might be smaller than the experimental accuracy, so that the amorphous material might look like a true, homogeneous ferromagnet. Only this is probably rarer than might seem from the literature, because many of the reported sharp transitions are evidently caused by Arrott plots extrapolations from too high fields.
Magnetostriction of Co-base amorphous alloys and high frequency permeability in their sputtered thin films (invited)
Authors: Fujimori Hiroyasu , Kazama Noriaki S. , Hirose Kenji , Zhang Jiaji , Morita Hiroaki , Sato Isamu , Sugawara Hiroshi
Published: February 2003

For new magnetic materials with high permeability at MHz frequencies as well as high magnetic induction, magnetic properties of Co-base amorphous alloys produced by a sputtering technique were investigated. Small magnetostrictions, important for this purpose, were found in the Co-Nb-Ti system and Co-(Fe, Mn)-Nb system. The dipole-type model explained the concentration dependence of magnetostriction. In order to increase permeability at high frequencies by reducing eddy current losses, these amorphous alloys were made into thin film form. It was found that dc coercivity for the single film (about 3 μm thick) of Co80 Nb20 with negative magnetostriction was larger than that for Co80Ti20 with positive magnetostriction, while the layered films of Co80Nb20 separated by a SiO2 insulator showed small coercivities. Permeabilities of about 4×103 at 1 MHz and 1×103 at 10 MHz were obtained in the Co80Nb20/SiO2 and Co80Ti20/SiO2 layered films.
Temperature dependence of creep-induced and field-induced anisotropy in a zero magnetostriction amorphous alloy
Authors: Flanders P. J. , Morito N.
Published: February 2003

The creep-induced anisotropy Kc, the field-induced anisotropy Kf, and the saturation magnetization Ms have been measured from 77 to 300 K on a zero-magnetostriction cobalt-based amorphous alloy. The temperature dependence of both anisotropies can be expressed as K=kMn, with n=2.6±0.1. Since both anisotropies have the same temperature dependence, they presumably have the same structural origin, namely anelastic structural defects or shearable components, even though they are different in magnitude by a factor of 10.
Magnetostriction and the local order of Co-Nb-B glasses
Authors: Corb B. W. , O’Handley R. C. , Paradis S. , Grant N. J.
Published: February 2003

The saturation magnetostriction λs for Co80NbxB20−x glasses increases smoothly from −4×10−6 to zero as B is replaced by Nb. The temperature dependence of λs in two Co-Nb-B glasses vanishes abruptly near 150 °C, several hundred degrees below TC . These data cannot be fit with combinations of one-ion and two-ion components. Rather, we believe this result to be a reflection in ‖λs‖ of a local structural transformation observed in these glasses.
Mechanical properties and magnetic behavior of deformed metal glass wires
Authors: Chen H. S. , Sherwood R. C. , Jin S. , Chi G. C. , Inoue A. , Masumoto T. , Hagiwara H.
Published: February 2003

Fe75B15Si10 and Co72.5B15Si12.5 glass wires, when cold-drawn, exhibit high magnetic squareness and coercive forces ranging from 1.0 to 20 Oe. These wires, upon magnetic switching in a pickup coil, produce a sharp voltage pulse of ∼6 V/cm2 turn. The Young’s modulus E, ΔE effects, fracture strength σf, and ac coercive force Hac of these wires in as-quenched and cold-drawn states are presented.
The effect of flash annealing on the magnetic properties of amorphous alloys (invited; abstract)
Authors: Jagielinski T.
Published: February 2003

The effect of flash annealing due to resistive heating by short electric current pulses flowing through an amorphous alloy sample was studied. The heat and cooling rates of the order 104–105 K/s, and the maximum heating temperature of 1200 K (estimated in two different ways) were attained without causing crystallization. Magnetic properties such as the initial permeability, coercive field, or disaccommodation of as-quenched and/or preannealed samples were improved within less than 100 ms of heat treatment. The induced anisotropy was also easily wiped out without deteriorating the Ku kinetics and mechanical properties of the sample. The reversibility of the Ku kinetics is shown by the flash annealing technique. The Curie temperature was reversibly changed over a range wider than achieved by conventional heat treatment.
Reversibility of the structural relaxation in amorphous alloys
Authors: Jagielinski T. , Egami T.
Published: February 2003

Changes in volume, Curie temperature, field induced anisotropy, and elastic constant due to the structural relaxation induced by annealing are compared for metal-metalloid glasses. It is shown that the volume relaxation and other relaxation phenomena have different kinetics, therefore at least two parameters are necessary to describe the internal state of the metallic glasses. The results are discussed in terms of the recently proposed theory of local structural fluctuations.
Temperature and frequency dependence of microwave magnetic properties of amorphous Fe100−xBx
Authors: Heinrich B. , Rudd J. M. , Urquhart K. , Myrtle K. , Cochran J. F. , Hasegawa R.
Published: February 2003

Ferromagnetic resonance linewidths, ΔH, have been measured at 9.5, 24, 38, and 73 GHz for a series of amorphous iron-boron ribbons with compositions, Fe100−xBx (x=14 to 22). Transmission measurements at 73 GHz have also been carried out to establish the contribution of the bulk intrinsic damping to the frequency dependence of the FMR linewidth. All measurements were carried out over a temperature range of 20–350 °C. The linewidths of the present specimens could be approximately represented by an expression of the form ΔH=ΔH0+(slope)×f; this observation is in agreement with the results reported on the commercial ribbons. The slope was found to be in agreement with the contribution from the intrinsic Landau–Lifshitz damping as measured by transmission. The Landau–Lifshitz damping was found to increase with decreasing boron concentration.
Percolation-like behavior of the spin wave stiffness in amorphous (FepNi1−p)80P20
Authors: Meichle L. S. , Salamon M. B.
Published: February 2003

The spin wave stiffness D and the phase diagram have been determined for the series of amorphous (FepNi1−p)80P20 alloys, from magnetization data. For applied fields greater than 1 kOe, the magnetization follows the Bloch T3/2 law when corrected for field-induced gap. The coefficient of the T3/2 term diverges as the concentration is reduced towards the critical concentration pc. The effective range parameter D/Tc is also found to diverge, as (p−pc)−1/2. This is consistent with current models for the spin wave stiffness in percolating magnets.
Mössbauer study of sputtered Fe-Ti alloys with wide composition range
Authors: Liou S. H. , Chien C. L.
Published: February 2003

FexTi100−x alloys over a wide composition range has been made by high-rate sputtering and studied by 57Fe Mössbauer spectroscopy. Samples with 30≤x≤80 are amorphous whereas samples with x≥85 are metastable crystalline bcc alloys. Large differences in magnetic properties (e.g., TC) and hyperfine interactions (Heff, isomer shift) are found between the amorphous and bcc alloys. Comparison of FeTi and Fe2Ti in amorphous and crystalline states show that the short-range order in the amorphous state has no resemblence to that of the crystalline compounds.
Temperature dependence of the field-induced magnetic form factor of the intermetallic compound PrSn3
Authors: Loong C.-K. , Stassis C. , Zarestky J. , McMasters O. D. , Moon R. M.
Published: February 2003

The spatial distribution of the magnetization induced by a magnetic field of 42.5 kG in a single crystal of PrSn3 has been studied at 100 and 20 K using polarized neutron scattering techniques. We find that at both temperatures the measured form factor is in good agreement with the theoretical 4f magnetic form factor of the Pr3+ ion. This result is in contrast to the large deviations from the 4f magnetic form factor of Ce3+ observed, at low temperatures, for the mixed-valence compounds CeSn3 and CePd3. The localized static susceptibility of PrSn3 at 100 and 20 K, obtained by extrapolating the measured form factor to the forward direction, agrees very well with bulk susceptibility measurements.
Stress-induced changes in the paramagnetic susceptibility and antiferromagnetic phase transition of DySb
Authors: Osterman D. P. , Williamson S. J. , Morin P.
Published: February 2003

The effects of [100] uniaxial compressive stress on the magnetic properties of DySb have been investigated for stress levels up to 420 MPa and temperatures between 4 and 65 K. Magnetic susceptibility measurements in low fields using a SQUID magnetometer show a reduction in the discontinuity at the first-order antiferromagnetic transition when stress is applied. Compression also shifts the transition upward in temperature at an initial rate of (1.16±0.07)×10−2 K/MPa. At a critical stress of 280±30 MPa the transition becomes second order. In the paramagnetic phase an increase in susceptibility is observed that becomes less pronounced at high temperatures. This result is in good agreement with the predictions of a mean-field theory that includes Heisenberg dipolar exchange and quadrupolar pair interactions.
Quantum effects in helimagnets: Disappearance of the soft mode at the wave vector of magnetic order
Authors: Rastelli E. , Reatto L. , Tassi A.
Published: February 2003

Usually the quantum nature of spins has only a limited effect on properties like the spin wave spectrum of a system and the S → ∞ limit (classical vectorial model) is often considered. On the contrary, we show that in helimagnets the quantum corrections can have dramatic effects. In absence of magnetic anisotropy the spin wave spectrum in the S → ∞ limit vanishes at the wave vectors k=±Q, Q being the wave vector characterizing the helical order. We find that this soft mode is destroyed by quantum effects and also the magnitude of Q can be modified significantly. Moreover, even any structure in the spectrum for k∼±Q is very easily eliminated for Hamiltonian parameters of physical interest. The model we consider which we call ANNNH model, is the quantum analogous of the well-known ANNNI model.
Magnetic excitations of the dilute one-dimensional magnet CsMnxMg1−xBr3
Authors: Furrer A. , Güdel H. U.
Published: February 2003

The inelastic neutron scattering technique was used to measure the magnetic excitation spectrum of the dilute one-dimensional magnet CsMnxMg1−xBr3 in the low-concentration limit (x=0.14, 0.28). The observed energy spectra exhibit a series of well-resolved peaks which are interpreted in terms of transitions within clusters of dimers and trimers of Mn2+ ions arranged along the c axis. The observed exchange splittings are directly related to the exchange interactions. In the Heisenberg picture the nearest-neighbor and next-nearest-neighbor exchange parameters are determined to be J=−0.89±0.02 meV and J′=−0.04±0.02 meV, respectively. Spin-wave theory turns out to be inadequate for studying the spin dynamics of small clusters.
Brillouin scattering from parallel pump instabilities in YIG (abstract)
Authors: Wettling W. , Wilber W. D. , Kabos P. , Patton C. E.
Published: February 2003

Brillouin light scattering has been observed from parametrically excited magnons by parallel pumping in a 4-μ yttrium iron garnet film at 9.4 GHz. Scattering from the spin-waves could be observed continuously from the thermal level through the nonlinear region of parametrically excited magnons. Magnons with small wave vectors propagating perpendicular to the static field are seen to have the lowest critical field as predicted theoretically. The spectra of these parametric excitations show a pronounced structure.
Dynamics of itinerant ferromagnets above T
C (invited)
Authors: Shirane G. , Steinsvoll O. , Uemura Y. J. , Wicksted J.
Published: February 2003

A review is given of our current studies of the magnetic scattering, above TC, from Ni, Fe, and Fe (4%-Si). Reliable scattering functions S(Q,ω) are obtained up to 50 meV of energy transfer by combining polarized and unpolarized neutron techniques. Although constant E scans show magnon like peaks in agreement with the previous Oak Ridge data, no peaks are observed in our constant Q scans up to 0.5 Å−1, in contrast to the well defined peak reported by Lynn for Fe(12%-Si). Unexpectedly, for a wide temperature range, the scattering function S(Q,ω) takes a simple Lorentzian form S(Q,ω)∝(1/κ21+q2) ⋅ (Γ/Γ2+ ω2) , with Γ=Λq2, where Λ is the diffusion constant, and κ1 the inverse correlation range. At TC, where Γ=Aq2.5, this can be reduced to a universal scattering function q0.5/[q5+(ω/A)2]. This scaling gives an entirely new and unified interpretation of magnetic scattering from Ni, Fe, and all other isotropic cubic ferromagnets.
Magnetic structure of holmium
Authors: Pechan M. J. , Stassis C.
Published: February 2003

The magnetic structure of high purity single crystals of holmium has been studied by neutron diffraction techniques. Although the general characteristics of the magnetic structure have been found to agree with earlier measurements, some discrepancies have been resolved and new features have been observed. The magnetic form factor has been measured and compared with relativistic atomic calculations. The low temperature structure (T<20 K) is that of a conical ferromagnet with wave vector (1/6)(2π/c) along the c axis. The basal plane moment is 9.7 μB and the c-axis ferromagnetic component is 1.6 μB at T=6 K. Bunching of the basal plane moments around the easy hexagonal direction has been observed below T=50 K. Evidence for asphericity in the magnetization density is presented and discussed. The wave vector of the basal plane modulation decreases monotonically with temperature in general accordance with the Elliott–Wedgewood theory. Several inflection points were observed, however, which correspond to commensurability with the chemical lattice. The measured temperature dependence of the c- and a-axis lattice constants shows significant magnetostriction. The possibility of a c-axis modulated moment is discussed.
Spin split electronic states in Fe and Ni and their temperature dependence (invited; abstract)
Authors: Kisker E.
Published: February 2003

Spin-, energy-, and angle-resolved photoemission has recently allowed us to observe directly the exchange splitting of Fe and Ni at extremal points in the Brillouin zone [R. Feder, W. Gudat, E. Kisker, A. Rodrigurez, and K. Schroder, Solid State Commun. 46, 619 (1983); R. Raue, H. Hopster, and R. Clauberg, Phys. Rev. Lett. 50, 1623 (1983)]; Theoretical analysis reveals that for Fe, similar as for Ni, self-energy corrections due to the photoemission hole-state are important. For Ni(110), the spin resolved energy distribution curves (EDCs) have been studied as a function of the sample temperature between room temperature and TC [H. Hopster, R. Raue, G. Guntherodt, E. Kisker, R. Clauberg, and M. Campagna (unpublished)]. The observed changes of the spin resolved EDCs (peak separation and line shapes) are discussed in relation to different models for ferromagnetism at finite temperatures. Similar experiments are in progress in Fe(100) at the German storage ring BESSY, Berlin.
Orbital and covalency effects in magnetic neutron scattering from transition metal perovskites (abstract)
Authors: Khan D. C. , Sharma J. K.
Published: February 2003

A detailed analysis of the aspherical contribution to neutron scattering magnetic form factor due to unquenched orbital moment is undertaken for transition metal perovskites KMF3 (M=Fe++,Co++,Ni++) using the Trammell method. These results, along with results for the spherical form factor, are compared with the experimental data of Scatturin, Corliss, Elliot, and Hastings to identify the extent of the covalency effect. The covalency parameters λσ and λπ have been estimated for molecular orbital bonding using the Hubbard–Marshall method.
The role of coulomb interactions in valence transition: Falicov–Kimball model
Authors: Bowen Samuel P. , Lady S. C.
Published: February 2003

A nonperturbative method of Green function calculation is applied to the Falicov–Kimball model Hamiltonian. In an approximation to first order in the hopping matrix elements, self-consistent solutions for several thermal averages and correlation functions do not show abrupt phase changes as a function of temperature. This treatment suggests that the Coulomb correlation by itself is not the key ingredient to understanding valence transitions.
Inelastic neutron scattering from intermediate valence compounds
Authors: Huber D. L.
Published: February 2003

The results of a calculation of the high frequency limit of the dynamic structure factor characterizing the inelastic neutron scattering from intermediate valence compounds are presented. At high temperatures, the scattering is given by the decoupled-mode approximation, while at low temperatures a quasiparticle model is employed. The relevance of the theory to experimental studies in CeSn3 is discussed.
Thermodynamic properties of the Anderson model (invited)
Authors: Okiji Ayao , Kawakami Norio
Published: February 2003

It is shown that the Anderson Hamiltonian is one of the Hamiltonians which can be solved exactly by means of the Bethe ansatz method. The thermodynamic quantities calculated on the basis of the exact solution are the magnetic susceptibility and the electronic specific heat.
A revised diagrammatic technique for the degenerate Anderson model
Authors: Lee T. K. , Zhang F. C.
Published: February 2003

The Goldstone diagrammatic technique developed by Keiter and Kimball for single impurity Anderson model is reformulated. Instead of having the self-energy functions defined on the real axis as the Brillouin–Wigner theory, we have defined the functions on the complex plane. This avoids the complicated and cumbersome regularization procedure required in the Keiter and Kimball formulation. Most important of all it makes the numerical calculations possible. The exact partition function may be written down in terms of irreducible self-energy diagrams. The Green function and spectral function are derived.
Electronic transport properties of La-Al metallic glasses
Authors: Tsai C. L. , Lu F. C.
Published: February 2003

Electronic transport properties such as ρ, RH, and Δρ/ρ have been measured for La-Al metallic glasses over a wide temperature range and in a magnetic field up to 15 T. The positive Δρ/ρ with a (H/T)1/2 dependence in the high field limit indicates the dominance of electron interaction effect in the transport properties of La-Al metallic glasses, therefore the electron interaction is responsible for the negative α at low temperatures. The Mott s-d scattering, however, is the most likely explanation for the large ρ, the positive RH, and negative TEP.