bluuebunny/crossref_metadata_2025 huggingface dataset:
Universal low-temperature properties of normal heavy-fermion systems (invited)
Authors: Auerbach Assa , Levin K.
Published: July 2002

We present a microscopic derivation of the Fermi-liquid properties of the Anderson lattice. Our calculations suggest that the low-temperature state of the normal heavy Fermi liquid has a number of universal features, for which there is good experimental evidence. Using the Kondo-boson 1/N expansion, we find the Fermi liquid is characterized by the mean-field ‘‘bare’’ particles (which are heavy) and their respective interactions. The latter are mediated by fluctuations in the f-level position and valence-conduction electron hybridization. Our calculations lead to the following experimental predictions: (i) the low-temperature specific heat behaves as C=γT∝T/TK with corrections ΔC=(T/TK)3 ln(T/TK), (ii) the zero-temperature spin susceptibility χ∝1/TK, and (iii) the resistivity ρ∝(T/TK)2. These results all contain a unique energy scale TK which is proportional to the inverse effective mass. Experimental support for these predictions is provided by evidence of systematic scaling of χ and ρ with γ throughout the entire class of heavy-fermion compounds. In addition we analyze recent pressure-dependent specific-heat measurements on UPt3 combined with χ and ρ data to confirm the scaling of these quantities with a single strongly pressure-dependent energy scale. This analysis provides evidence against current ferromagnetic spin-fluctuation theories.
Strong electron-phonon interactions in mixed valent states
Authors: Riseborough Peter S.
Published: July 2002

We examine the effects that strong electron-phonon coupling has on the electronic density of states and the phonon spectrum of the mixed valent phase. We examine the dependence of the polaronic properties on the position of the f level relative to the Fermi level.
Tb-F emission centers in ZnS:Tb,F thin-film electroluminescent devices
Authors: Mikami Akiyoshi , Ogura Takashi , Tanaka Koichi , Taniguchi Koji , Yoshida Masaru , Nakajima Shigeo
Published: July 2002

The relative amount of fluorine(F) to terbium(Tb), F/Tb, in a ZnS:Tb,F electroluminescent film deposited by rf-sputtering method sensitively varies with Tb concentration and preparation conditions. Values of F/Tb are about 1 for the films with low Tb concentrations below 0.5 at. % or the films annealed at 600 °C. The presence of a TbF3 molecular center is inconceivable except for the nonannealed films with relatively high Tb concentrations. It was clarified that variations of the emission spectra and the decay rate with Tb concentration are attributed to the change of F/Tb in the ZnS film. Furthermore, the surprising result is that the Tb-F center has the better emission efficiency, rather than the TbF3 center. A brightness exceeding 600 ft L was obtained under 1-kHz pulse excitation by adjusting the concentration ratio F/Tb to about 1. The real nature of the Tb-F center as well as the role of F− ions are discussed.
Surface alloying in stainless steel and Ni-20% Fe by pulsed laser irradiation
Authors: Laursen T. , Whitton J. L. , Nilson J. A. , Nip Wing , Mitchell I. V. , Plattner H. H. , Swanson M. L.
Published: July 2002

Surface alloys have been produced by pulsed laser irradiation of thin metal overlayers (Au and Mo) on austenitic stainless steel and Ni-20% Fe. The structure and composition of the surface alloys have been characterized by Rutherford backscattering and ion channeling. The stainless-steel alloy has a thin surface layer with nonsubstitutional Au or Mo on top of the substitutional alloy. Metastable solid solutions of gold are formed with concentration levels as high as 5 at. % in stainless steel and 28 at. % in Ni-20% Fe. The laser alloying process involves surface melting and, in some cases, the formation of ∼1-μm-high ridges. The quality of the epitaxial regrowth, as seen in the channeling spectra, ranges from good to very poor. Dechanneling in the alloyed surface has a complex behavior and is dependent on the energy density used for the irradiation. It is also important whether or not the irradiation is carried out in air or in flowing helium. The use of flowing helium instead of air has a striking reverse effect on the two alloy systems; it reduces the lattice disorder of alloys formed by Au and stainless steel, while an increase in disorder is seen when Au is alloyed with Ni-20% Fe.
Initial generation kinetics of oxygen-related thermal donors at 430 °C in silicon
Authors: Kamiura Yoichi , Hashimoto Fumio , Endo Kazuyoshi
Published: July 2002

The initial generation kinetics of thermal donors at 430 °C in Czochralski-grown silicon crystals containing (3–10)×1017 interstitial oxygen atoms per cm3 is studied by careful resistivity measurements at room temperature. The density of thermal donors is measured over the range from 1013 to 1016 cm−3. An analysis based on the chemical rate theory is made. For as-grown crystals, the well-known dependence of the initial donor formation rate and the maximum donor density on the initial oxygen concentration is confirmed. However, some irregularities are present in the very initial period of donor generation, probably arising from differences in thermal history of as-grown crystals. These irregularities are completely removed by pre-heating as-grown crystals at 1300 °C for 22 h and rapidly quenching them. In such heat-treated crystals, the initial kinetics of the thermal donor generation process can be described well by the following reaction scheme. The smallest donor species involving five oxygen atoms is preferentially formed, with its density being proportional to the square of the annealing time. Also, the electrically inactive cluster that involves four oxygen atoms and can be converted into the donor by the addition of an oxygen atom is simultaneously generated, while the formation and dissociation reactions for the smaller neutral clusters involving two and three oxygen atoms maintain the equilibrium. In as-grown crystals, the same reaction scheme can also explain the initial kinetics very well only if the initial densities of the smallest donor and the smaller neutral clusters are significantly increased, indicating that the initial irregularities are due to the differences in the densities of preexisting donors and neutral clusters.
Damage induced by laser irradiation of NiSi2/Si 〈111〉 structures
Authors: Priolo F. , Grimaldi M. G. , Baeri P. , Rimini E. , La Mantia A.
Published: July 2002

Thermally grown NiSi2 layers on 〈111〉 Si substrates were irradiated with single pulses of a Q-switched Nd laser. Melting and solidification dynamics, orientation and structure of the irradiated layers were investigated by in situ time-resolved reflectivity, Rutherford backscattering in combination with channeling and scanning electron microscopy. Melt starts from the surface at 0.35 J/cm2. When the energy density is enough to melt the entire layer, the epitaxially solidified NiSi2 is mainly of B-type orientation. The thermally grown or partially melted layers are a mixture of A- and B-type crystals. A substantial decrease in the reflectivity signal has been found in the case of a partial melting of the thermally grown NiSi2 layers several microseconds after the laser pulse. This decrease has been correlated with the exfoliation of surface materials as found by the scanning electron microscopy of the irradiated samples. Slip planes were also observed after solidification either of a partially melted mixture of A and B type or of a B-type NiSi2 silicide. No exfoliation and a much lower density of slip planes were observed after solidification of a completely melted silicide layer. The dynamics of melting and the damage of the irradiated layers are explained in terms of heat-flow calculation and thermomechanical and mismatch stress.
Defect levels in electrodeposited n-type CdTe thin films
Authors: So S. M. , Hwang W. , Meyers P. V. , Liu C. H.
Published: July 2002

Admittance spectroscopy is used to measure electron traps near the conduction band of the n-type electrodeposited CdTe thin films. Several samples of Ni-CdTe Schottky-barrier and Ni-TeO2-CdTe devices are used in the measurement. Two donor levels with activation energies around 0.12 eV and between 0.19 and 0.26 eV are detected. In addition, there may be one or more shallow donor levels within 0.04 eV from the conduction band. Capacitance loops are observed in the capacitance-voltage measurements performed at different temperatures and bias sweep rates. The activation energies, densities, and electron-capture cross sections of the two slow electron-trap levels responding to the cyclical ramp bias are estimated. The rise and decay photocapacitance transient measurements at 295 K reveal two electron-trap levels with photoionization threshold energies of 0.8 and 1.3 eV. These two levels are suspected to correspond to the other two slow electron-trap levels estimated in the capacitance-voltage measurement and located around or above the midgap. The differences between thermal and optical ionization energies and the slow electron-capture rates of these two levels may be explained by the nonradiative, thermally activated capture processes with large lattice relaxation. Numerous defects around and below the midgap are detected by the steady-state photocapacitance measurement at 100 K. A band of seven defect levels spreading within 0.6 to 1.0 eV is observed. Large capacitance changes are recorded at 1.37, 1.41, and 1.45 eV. These three levels are speculated to be the major compensating acceptor levels. Based on both the photocurrent and photocapacitance measurements, electrons emitted from the 1.02-, 1.06-, 1.21-, and 1.28-eV levels are believed to arise from the defects at the TeO2-CdTe interface.
Preparation of doped hydrogenated amorphous silicon films by microwave electron-cyclotron-resonance plasma discharge deposition
Authors: Kitagawa M. , Setsune K. , Manabe Y. , Hirao T.
Published: July 2002

Phosphorus- and boron-doped hydrogenated amorphous silicon films were deposited by microwave electron-cyclotron-resonance plasma discharge. Electrical and optical properties of the films have been investigated. Low conductivity such as 10−8–10−7 (Ω cm)−1 was obtained for the as-grown films deposited without heating. The dark conductivity gradually increased by subsequent annealing steps up to 300 °C. After 300 °C annealing, conductivities of about 10−4 (Ω cm)−1 and optical gaps of 1.9 eV were obtained for both P-doped and B-doped films. Our doped a-Si:H films are expected to play the role of effective window layers of solar cells.
Tunneling-assisted impact ionization for a superlattice
Authors: Chuang S. L. , Hess K.
Published: July 2002

Tunneling-assisted impact ionization across the conduction-band-edge discontinuity of quantum-well heterostructures is investigated and applied to a new superlattice structure. We consider multiquantum-well structures where the quantum-well regions are heavily doped and the undoped barrier regions are essentially insulating. Incident hot electrons due to the applied electric field perpendicular to the heterointerface interact with the two-dimensional electrons confined to the quantum wells through Coulomb force. The resultant electrons can either have enough energy to get out of the wells or tunnel through the triangular barriers. A new analytical approximation for the impact ionization rate is given which compares favorably with numerical results. The tunneling-assisted impact ionization rates and the ionization coefficients are calculated. It is shown that the tunneling effect reduces the ionization threshold and enhances the ionization rate significantly.
Formation, optical properties, and laser operation of F−2 centers in LiF
Authors: Gellermann W. , Müller A. , Wandt D. , Wilk S. , Luty F.
Published: July 2002

Formation conditions, optical properties, and lasing behavior of F−2 color centers in LiF crystals are investigated. The optical pumping cycle of the three-electron defect is found to involve intermediate transitions of small efficiency into some metastable energy levels (having a lifetime of several seconds). This process could either be intrinsic to the F−2 defects (e.g., intersystem crossing into quartet states) or it could be caused by (low efficiency) optical ionization of F−2 centers and electron capture in unstable traps. While cw laser oscillation is prevented by a resulting bottleneck, efficient tunable pulsed laser operation in the 1.1–1.2-μm range is possible at room temperature.
Annealing behavior of implanted Si in semi-insulating GaAs in the presence of stress
Authors: Otsuki T.
Published: July 2002

A thermodynamic theory of the annealing behavior of Si impurities in GaAs is presented. It is predicted that the ratio of the number of Si impurities at the Ga sites to that at the As sites is sensitive to the stress under which annealing or doping is performed. The ratio is above and below unity under a compressive stress and tensile stress exceeding a critical value, respectively. Therefore, the Si impurities act predominantly as donors and acceptors under the respective stresses. The theory is supported by our experimental finding that the Si-implanted GaAs becomes of p type by annealing under a tensile stress.
Kinetics of the order-disorder transformation in Pt1Co1
Authors: Orehotsky J. , Orehotsky J. Larsen
Published: July 2002

The kinetics of the order–disorder transformation in Pt1Co1 were investigated at various temperatures between 615 and 719 °C by magnetization measurements. Atomic ordering in Pt1Co1 was found to obey a first-order kinetic equation whose time constant in an Arrhenius function of temperature with an associated activation energy of 58 kcal/mol. An unexplained initial transient was apparent also in the kinetic response data.
Transverse Young modulus of a composite with nonregular structure
Authors: Guy M. I. , Turusov R. A. , Manevitch L. I. , Oshmjan V. G. , Zelensky E. S. , Sochnev V. I. , Suljaeva Z. P.
Published: July 2002

This paper considers the transverse Young modulus of specially constructed ‘‘plane’’ composites for various volume fractions of filler. It was determined that the sharp increase of composite elastic stiffness in a narrow concentration region relates to the material’s percolation peculiarities.
Donor-cation vacancy complex in Si-doped AlGaAs grown by metalorganic chemical vapor deposition
Authors: Oh-hori Tatsuya , Itoh Hiromi , Tanaka Hitoshi , Kasai Kazumi , Takikawa Masahiko , Komeno Junji
Published: July 2002

The donor-cation vacancy complex in Si-doped AlGaAs grown by metalorganic chemical vapor deposition has been identified by examining the growth-condition dependence of photoluminescence (PL) spectra. It has been revealed that the complex has the same origin as the self-activated center in GaAs, and is relevant to the degradation of crystal quality for high doping and high V/III ratio conditions. The excitation intensity dependence of PL spectra, and the fact that the emission is not observed for the samples with indirect gaps, suggest that the emission is a band-to-acceptor transition. The temperature dependence of the emission intensity and linewidth are compared with GaAs.
A new wafer-level isothermal Joule-heated electromigration test for rapid testing of integrated-circuit interconnect
Authors: Jones Robert E. , Smith Larry D.
Published: July 2002

We report on a new wafer-level isothermal Joule-heated electromigration test which allows rapid testing of integrated-circuit interconnects. This test can be used to investigate the temperature dependence of electromigration lifetimes. As a demonstration of the test, lifetimes of Al-1% Si lines were measured over the temperature range 200–400 °C. The lifetime results are consistent with an inverse-square current dependence and with an activation energy of 1.4 eV at higher temperatures (above about 345 °C) and 0.6 eV at lower temperatures. This is in agreement with a model of grain-boundary diffusion dominating the transport at lower temperatures with bulk diffusion dominating at higher temperatures. Numerical thermal models for Joule-heated test lines are used to investigate deviations from isothermal conditions for several practical situations. Various rapid electromigration tests are compared, and we show this new test can obtain the maximum possible electromigration lifetime test acceleration, while restricting test conditions to the lower-temperature grain-boundary dominated transport.
Breakdown of scaling in the 1D spin-1/2 Heisenberg ferromagnet
Authors: Bonner Jill C. , Müller Gerhard
Published: July 2002

The problem of the critical behavior of the spin-1/2 Heisenberg ferromagnetic chain has challenged many research workers since 1964. We discuss the critical exponents α and γ recently determined by Schlottmann and by Takahashi and Yamada in the context of previously known Tc=0 critical properties of the 1D s=1/2 XXZ model and the classical Heisenberg model, and we comment on the manifest breakdown of scaling in the s=1/2 Heisenberg ferromagnet.
The electron temperature in the plasma of a spark-recombination laser
Authors: Villagrán M. , Gallardo M. , Tocho J. O. , Rocca J. J.
Published: July 2002

The electron temperature in an expanding spark plasma used as active medium in a cadmium-recombination laser was measured using the relative intensities of helium lines originated from levels in local thermodynamic equilibrium. Measurements resolved in space and time show that the electron temperature at the conditions of maximum gain are 1000 and 600 K at 5 and 10 mm of the sparks, respectively. Rapid cooling occurs after the termination of the discharge-current pulse, and the electron temperature reaches values below 1000 K. Subsequently, the electron temperature decrease is slow. The optical gain calculated for the 1.43-μm Cd (I)-recombination-laser transition using the measured electron temperature and particle density values is 3×10−3 cm−1, in good agreement with measurements.
Magnetotransport in (UxCe1−x)2Zn17 alloys
Authors: McAlister S. P. , Olivier M. , Siegrist T.
Published: July 2002

U2Zn17 is a heavy fermion antiferromagnet, whereas Ce2Zn17 is an antiferromagnet with TN≂1.67 K. The system (UxCe1−x)2Zn17, therefore, allows a study of the evolution of the heavy fermion state in a magnetic system. We report magnetic and magnetotransport measurements of alloys with x=0, 0.04, 0.55, and 0.90, from 0.35 to 295 K. The effective paramagnetic moment of these alloys varies monotonically with x. Resistivity measurements reveal concentrated Kondo behavior in the Ce-rich compounds (x=0 and 0.04). A marked difference is found in the temperature dependence of the electrical resistivity of the compounds near the U-rich end. In contrast to the large drop seen in U2Zn17, an increase is observed in (U0.9Ce0.1)2Zn17.
Optical imaging of magnetic domains in motion (invited)
Authors: Argyle B. E. , Petek B. , Herman D. A.
Published: July 2002

We describe a laser magneto-optic microscope (LAMOM) system, used to observe magnetic domain dynamics in Permalloy thin-film devices. Optimization of Kerr magneto-optic contrast is achieved by using laser illumination in a polarized light microscope in combination with video image processing. High magnetic contrast, a diffraction-limited (0.25 μm) resolution, and motion picture recording capability at up to 30 frames/s are demonstrated by recent results.
Electrical resistivity and specific heat studies of Nd-Fe-B magnet around its T
C
Authors: Jen S. U. , Yao Y. D.
Published: July 2002

The electrical resistivity and specific heat properties of two Nd-Fe-B alloys samples, Nd5Fe62B33 and Nd15Fe77B8, have been investigated between 300 and 700 K. Both electrical resistivity and specific heat of Nd15Fe77B8 has shown an anomalous behavior near 566 K, while that of Nd5Fe62B33 is less clear and smeared out. The simple power law C=Aε−α +B has been used to fit the specific heat data of Nd15Fe77B8 for the critical indices α and α′. The Curie temperature of Nd15Fe77B8 determined experimentally is 566 K. From electrical resistivity data near 566 K of both materials, Nd5Fe62B33 shows only a minute bending in dρ/dT, but Nd15Fe77B8 behaves drastically different and is similar to the type III ferromagnet.
High-voltage Lorentz electron microscopy of Fe-Nd-B magnets (abstract)
Authors: Ramesh R. , Thomas G.
Published: July 2002

Magnetic domains in recently developed Fe-Nd-B permanent magnets have been investigated by high-voltage Lorentz electron microscopy to understand the interaction of domain walls with microstructural features. Specifically, the interaction of the domain walls with the nonmagnetic fcc phase and grain boundaries have been investigated. Samples with the c axis in the plane of the foil and normal to it have been investigated. Domain wall widths have been measured from defocussing experiments in the Fresnel mode. The wall widths experimentally determined compare well with those predicted from theoretical calculations. In the case of foils with the c axis in the plane of the foil, the domains are wider. Also, the domain wall image width changes from point to point, although there is no change in foil thickness. The walls in these foils could be moved by tilting the foil (thus varying the in-plane field of the objective lens). By this method, the interaction of the domain walls with microstructural features was studied. Results of all these experiments will be presented in this paper.
Signal-noise performance of 1–4-μm-wide multilayer M-R transducers
Authors: Pohm A. V. , Movall P. , Comstock C. S.
Published: July 2002

Signal-to-noise ratio measurements were performed on 0.75-, 1.25-, 1.5-, 2.0-, and 4.0-μm-wide end-on magnetoresistive (M-R) transducers made from multilayer magnetic films. The transducers had length-to-width ratios of 10 and 100. From experimental results, the calculated signal-to-noise performance of in-gap transducers with a length-to-width ratio of 10 was 34±2 dB. Measured signal-to-noise ratios of uniformly driven transducers with length-to-width ratios of 100 was 47±2 dB and transducers with a 10 to 1 ratio was 35±2 dB.
Temperature rise and burnout currents in 1–4-μm-wide multilayer head transducers
Authors: Comstock C. S. , Lutz J. , Pohm A. V. , Irwin S. A.
Published: July 2002

The temperature rise induced by sense currents and the sense burnout currents were measured for 0.75-, 1.25-, 2.0-, and 4.0-μm-wide end-on multilayer M-R head transducers. For the test elements, the burnout currents were approximately 12 mA per micron of width; nominal operating currents were less than 4 mA per micron of width. At the nominal operating currents, the temperature rise in the 0.75-μm-wide element was 23 °C. For the 1.25-, 2.0-, and 4.0-μm-wide elements, temperature rise was less than 10 °C.
Fiber optic interferometric and ferromagnetic resonance studies of Fe81B13.5Si3.5C2
Authors: Bobb L. , White B. , Tyagi S. , Larson D. C.
Published: July 2002

Amorphous films 3.5 μm thick of Fe81B13.5Si3.5C2 were deposited using conventional radio-frequency sputtering on planar glass substrates and cladded single-mode optical fibers of 80-μm diameter with a core diameter of 4 μm. The substrates were arranged in two configurations. In the first configuration the substrates (group I) were placed in contact with the water-cooled substrate table; in the second configuration (group II) the substrates were suspended about 8 mm above the substrate table. Ferromagnetic resonance (FMR) and vibrating sample magnetometer (VSM) measurements were used to study the bulk properties of the film and the longitudinal magneto-optical Kerr effect was used to study the magnetic hysteresis at the film surfaces. The group (I) samples were found to be magnetically softer than their group (II) counterparts. The magnetostrictive response of the coated fibers was studied using a Mach–Zehnder interferometer. The dependence of this response on annealing is also discussed.
Design and fabrication of thin-film heads based on a dry process (invited)
Authors: Hanazono M. , Narishige S. , Hara S. , Mitsuoka K. , Kawakami K. , Sugita Y. , Kuwatsuka S. , Kobayashi T. , Ohura M. , Tsuji Y.
Published: July 2002

High performance thin-film heads for disk drive systems have been developed based on a dry process. Heads were computer simulated and optimal design was carried out. Relationships among Ni-Fe composition, domain structure and wiggle of the read-write waveform were obtained. Based on these results, optimum Ni-Fe composition range was determined. A planarization procedure for an inbedding insulator of the conductor coil was developed. Also narrow track patterning and gap depth controlling procedures were developed. Using these procedures, a two-layered seventeen-turn thin-film head for a large capacity disk drive system (23 Mb/in.2) has been developed. The head exhibited excellent read-write characteristics.
Thin-film permanent magnet requirements for magnetic devices in MMIC (invited) (abstract)
Authors: Stancil D. D.
Published: July 2002

Sputtered permanent-magnet thin films1 may offer an attractive alternative to bulk permanent magnets for biasing microwave magnetic devices. Such films could significantly reduce the size, weight, and cost of these devices in geometries compatible with MMIC. A film of uniform thickness magnetized normal to its plane would only generate strong external fields near its edges, however, and so would not be effective for bias purposes. Thus uniform films with in-plane remnant moments are of primary interest. (Normally magnetized films with nonuniform thicknesses may be useful in cladding layers for flux confinement, but are not considered here.) Although field inhomogeneities inherent in the use of thin-film permanent magnets may be a problem for some resonant devices, below-resonance devices should be tolerant of inhomogeneities so long as the net internal field in the ferrite is small compared to the saturation magnetization, and ω>γ4πM. Examples are discussed suggesting how such films could be used to bias phase shifters, circulators, and magnetostatic wave devices.
Spectroscopy of RKKY spin glasses (abstract)
Authors: Lévy Laurent P. , Ogielski Andrew T.
Published: July 2002

We have measured the nonlinear susceptibilities χ4, χ6, χ8 of dilute AgMn spin glasses above and below the transition temperature Tg as a function of temperature, magnetic field, and frequency. In the static limit, these quantities display very well-defined singularities at Tg with very weak magnetic field dependence. At very low frequencies, we show that the nonlinear susceptibilities χ2n can be related to 2n spin-spin correlation functions by Kubo formulas, and that their measured critical exponents are consistent with the usual scaling hypothesis. Thus, we can infer β=0.9, γ=2.1, and δ=3.0. The nonlinear susceptibilities scale above the transition as power laws of frequency with exponents which depend weakly on temperature. To relate these exponents by dynamic scaling require several ansatz which validity are investigated. In a magnetic field, only one singularity is observed at the same temperature Tg as in zero field, but the frequency dependence of the nonlinear susceptibilities weakens below the transition. We also discuss the frequency dependence of the linear and nonlinear susceptibilities below the spin-glass transition.
Experimental cross-talk comparison of longitudinal and vertical recording
Authors: George P. K.
Published: July 2002

Measurements of the cross talk between adjacent tracks are made for a ring head on thin-film longitudinal, single-layer vertical, and double-layer vertical media. Similar measurements are made for a pole head on a double-layer medium. The results are summarized in terms of a spacing loss-like coefficient γ(dB/μm) which characterizes the linear portion of the track scan at the adjacent track location. Results are presented for the read and write widths of the heads and for the geometrical parameters of the pole pieces. A discussion of the relationship between experimental results and existing theoretical calculations is given.
A vector phenomenological model for digital recording
Authors: Della Torre E.
Published: July 2002

A vector phenomenological model is used to analyze digitally recorded magnetization transitions. The model assumes that a field along a principal axis magnetizes the media along that axis, while a field perpendicular to that axis demagnetizes it. The magnetizing process divides a calculation plane into four regions: the region that is magnetized positively, the region that is magnetized negatively, the region that is demagnetized, and the region that is unaffected by the process. The magnetization is then calculated as the integral of the magnetization density function over the positively magnetized region minus the integral of the density function over the negatively magnetized region plus the magnetization of the unaffected region. The calculations presented here are obtained from a simplification of the more general Preisach-like three-dimensional model.
Solution of cyclic nonlinear magnetic fields in three dimensions
Authors: Hoole S. Ratnajeevan H. , Shin Young Kil
Published: July 2002

Sinusoidally excited power frequency magnetic fields are governed by the diffusion equation and are usually analyzed by converting to complex phasors. Under nonlinear conditions however, such a mapping is not valid and the solution is by time stepping, with the attendant problems of finding a suitable starting point and build up of difference error in time. In this paper, for spatially two-dimensional problems, we consider time as a third coordinate and close the problem region by using the same node numbers at the end of one cycle or, alternatively, at the end of half a cycle with a mapping to the nodes at the start. Such a three-dimensional region is divided into finite elements with suitable interpolation nodes and the diffusion equation is solved by a Galerkin formulation. The method is applicable to any cyclic problem governed by the diffusion equation.
Computer-aided design and analysis of electrical machinery and devices (abstract)
Authors: Chari M. V. K. , Bedrosian G. , D’Angelo J. , Berkery J. F. , Palmo M. A. , DeBlois A.
Published: July 2002

Recent years have witnessed a growing demand for economical and energy efficient designs of electrical machines and their reliability in operation. Improved performance prediction at the design stage helps achieve some or all of these objectives in a cost effective and efficient manner. With the advent of digital computers, it has become possible to achieve this goal with a high degree of accuracy and minimal turn around time. A design study for tradeoffs of cost versus efficiency and reliability requires the use of sophisticated computational tools. Traditionally computer programs have been designed with a view to provide the user multiple options in terms of analyses, data manipulation, and post-processing of results. These codes have tended to be large and have been generally implemented in a batch mode with long turn around times. In this paper, an alternative approach to the traditional computer analysis of electric machines is presented using an interactive user-friendly software package. A finite element electromagnetic analysis program is considered, as it is one of the more significant and difficult to implement codes required frequently for design use. The advantages of interactive and generalized engineering software for the application mentioned above are examined. The detailed steps of engineering design analysis of a rotating electrical machine carried out with the help of an integrated software is described.
The effect of Os addition on sputtered iron oxide films
Authors: Ishii O. , Yoshimura F. , Terada A. , Sato I.
Published: July 2002

The features of grain growth in Os-added iron oxide films are investigated for the purpose of developing high signal-to-noise ratio (SNR) magnetic recording media. The average grain size of sputter-deposited γ-Fe2O3 films is markedly decreased by Os addition. The grains grow during the reduction process, from α-Fe2O3 to Fe3O4, and maintain the same size in subsequent oxidation, from Fe3O4 to γ-Fe2O3. Moreover, the reduction temperature decreases by 100 °C above 0.88 at. % Os addition. As a result, the grain size of γ-Fe2O3 films decreases from 84 to 35 nm as the Os content increases from 0 to over 0.88 at. %. In addition to the refining effect, an accelerating effect on the reducing reaction brings about an increase in the saturation magnetization and in the squareness ratio of γ-Fe2O3 films. Consequently, an Os-added γ-Fe2O3 thin-film disk has higher output voltage and SNR than other disks.
Slope-intercept analysis of M-H curves for samples with mixed ferromagnetic and paramagnetic regions
Authors: Speliotis D. E. , Fernelius N. C.
Published: July 2002

Rigid disks for magnetic recording usually employ an aluminum alloy substrate coated with a Ni-P film of 10–15 μm thickness prepared by electroless chemical deposition, followed by the ferromagnetic recording film deposited chemically or by sputtering. Depending on the bath composition and the method of preparation, it is possible for the Ni-P underlayer to consist of intermixed ferromagnetic and paramagnetic regions. Furthermore, the magnetic structure of the Ni-P underlayer may change significantly with subsequent heat treatments experienced during the sputter deposition of the ferromagnetic layer and other protective layers such as chromium and carbon. The presence of a ferromagnetic component in the Ni-P underlayer is, of course, undesirable and detrimental to the recording performance of the disk. Furthermore, in order to measure correctly the magnetic characteristics of the recording films, it is necessary to subtract out all the magnetic effects of the substrate and underlayer. Subtracting out a straight line M vs H curve can lead to incorrect results if the Ni-P underlayer has a significant ferromagnetic component. In this paper, we show that a good estimate of the magnitude of the ferromagnetic part of the underlayer can be obtained by extrapolating the slope of the raw M vs H curve of the Ni-P plus aluminum composite to the intercept at H=0 (slope intercept). Several examples of this are given for Ni-P films exposed to different heat treatments.
Magnetic recording in the printing mode
Authors: Minuhin V. B.
Published: July 2002

The playback process of magnetic recording is the correlation between the magnetization pattern in the medium and the sensitivity function (the fringing field) of the readback transducer. The correlation is the optimal detection method for signals buried in the noise. Therefore, the obvious way to improve the performance of digital magnetic recording is to realize the potential of the inherently present correlation. Unfortunately, in traditional longitudinal recording systems, the medium magnetization is formed in the trailing zone of a write head field, and the recorded transition bears no resemblance to the whole fringing field of the head. Using perpendicular or isotropic medium, it is possible to imprint encoded 1’s by switching off the current in the winding of a ring head. The imprinted 1’s are then (ideally) copies of a whole fringing field of a ring head and look like ‘‘horse-shoe’’ patterns of magnetization. During readback these patterns correlate almost ideally with the sensitivity function of a ring head. An essential element of the technique is the resumption of the current in the opposite polarity as the imprinted pattern moves downstream. This continues the perpendicular magnetization at the trailing edge of the previously formed ‘‘horse-shoe’’ pattern and fills voids in the magnetization. We present experimental data illustrating this method.
Magnetic properties of high-efficiency core materials NC-M1 and NC-B1
Authors: Kubota T. , Miyoshi K. , Shimoyama Y. , Eguchi S.
Published: July 2002

The magnetic properties of high-efficiency core materials NC-M1 and NC-B1 were examined in connection with their performance when assembled in motor cores using the developed induction-type model motor. The efficiency of the model motor is better when these new steels are used owing mainly to the lower iron loss of the model motor. It is considered that lower iron loss of motor is achieved by lower alternating core loss at designed magnetic flux density, lower rotational core loss beyond designed magnetic flux density, and lower core loss at high frequencies (beyond ∼500 Hz in the present model motor) of steels used. In view of the high-efficiency core materials, it is desirable for them to have improved crystalline texture and perhaps smaller grain size in order to obtain lower alternating core loss, lower rotational core loss, and lower core loss at high frequencies.
Persistence of magnetic surface anomalies in (110) Fe near an interface with MnF2 (abstract)
Authors: Stern G. P. , Qiu Z.-Q. , Tang H. , Walker J. C.
Published: July 2002

An anomalous quasilinear temperature dependence has been previously observed1 in the surface layers of Fe at an interface with MnF2. The (110) Fe was epitaxially grown to a thickness of about 50 layers on a (111) Ag substrate. The magnetic hyperfine field in the surface layers was probed by making the Fe sample from isotopically pure 56Fe and then growing the layer(s) of interest from 57Fe. Mössbauer spectroscopy is used to determine the magnetic hyperfine field on a layer-by-layer basis. For other interfaces besides MnF2 (for example, Ag, MgO) the surface layers of (110) Fe show a T3/2 dependence somewhat different from bulk. To better understand the unusual quasilinear behavior at the MnF2 interface, we have examined the temperature dependence of the magnetic hyperfine fields at layers somewhat deeper in the (110) Fe sample than the actual surface/interface. We report here measurements showing a linear temperature dependence for 57Fe layers at least five layers into the sample from the surface/interface. The slope of the Heff vs T curve is much smaller than for the surface region. Still deeper layers at least 10 layers into the sample from the surface/interface begin to show a T3/2 behavior which differs little from bulk values. We offer an explanation of this persistence of the surface effects into the deeper layers of the (110) Fe sample based on a surface anisotropy model. This explanation does not depend on the actual mechanism of the surface anisotropy and can remain valid if the source of the anisotropy is an exchange interaction between the surface Fe spins and the spins associated with the Mn ions in the MnF2.
Positron annihilation study of an Fe14Nd2B-type permanent magnet alloy (abstract)
Authors: Jones P. L. , Lind J. H. , El-Masry N. A. , Stadelmaier H. H. , Rothwarf F.
Published: July 2002

A Dy-substituted Fe14Nd2B-type permanent magnet alloy (Crumax 32) has been studied by positron annihilation lifetime spectroscopy, and also magnetic coercivity and microstructural analysis, to evaluate the effects of thermal treatment of the material. The results of this study show that the room temperature lifetime spectra can be modeled accurately using a partially constrained three-component fit. The variations in lifetime spectra induced by thermal treatment of the sintered magnet can be correlated with the concomitant decreases in coercivity and with a decrease in the surface area of free α-Fe as indicated by transmission electron microscopy.
Directional characteristics of field-annealed magnetoelastic amorphous metal magnetometers
Authors: Mermelstein M. D. , Dandridge A.
Published: July 2002

The directional characteristics of low-frequency magnetometers constructed from transversely field-annealed magnetoelastic amorphous metal ribbons has been investigated. The ribbon response is found to obey a cosine dependence to the field orientation relative to the ribbon longitudinal axis. This behavior is conducive to sensing both field direction and magnitude.
Study of low losses at high frequencies and low remanence for FeMoSiB metallic glasses (abstract)
Authors: Huang G. X. , Shi S. Y. , Xu Q. Z. , Yang G. B.
Published: July 2002

The effects of a new heat treatment technique and a conventional annealing process on the high-frequency core losses (20 kHz) of Fe76Mo3(SiB)21 amorphous alloys have been investigated. The result shows that the remanence and the high-frequency losses can be reduced remarkably by this special treatment. Meanwhile, its coercivity remains lower in the range of 2.39–4.79 (A/m). In studying, it is found that under the condition of this special treatment the phenomena of the enrichment and the depletion of atoms (Fe, Si, B) become more heavier, and the state between the surface layers of metallic glass core is changed, and the degree of partial crystallization of α-Fe can be controlled. The magnetic properties of Fe76Mo3(SiB)21 metallic glasses obtained by the treatment under the technological parameters selected properly are satisfied, as follows: Fe76Mo3(SiB)21—I P2/20 K =5.27 w/kg, P5/20 K =32.61 w/kg, B1=1.043 T, Hc1 =2.88 A/m, Br1/B1 =0.18. Fe76Mo3(SiB)21—I P2/20 K =5.59 w/kg, P5/20 K =37.25 w/kg, B1=0.656 T, Hc1 =4.79 A/m, Br1/B1 =0.11, in which the properties of high-frequency losses are superior to those of the conventional annealed alloys (P2/20 K =12–14 w/kg), and are comparable to those of VITROVAC Co66Fe4(MoSiB)30 and others.
Monte Carlo study of the Alexander–Anderson model
Authors: Hirsch J. E. , Lin H. Q.
Published: July 2002

We have studied the Alexander–Anderson model for two magnetic impurities in a metal using a numerical simulation technique. To demonstrate the accuracy of our method we compare simulation results with exact diagonalization results for a two-site conduction band. We study the model as a function of Coulomb interaction u=U/(πΔ)(Δ=hybridization width) and d-level position with respect to the Fermi level εd. We find that correlations between spins are always antiferromagnetic, contrary to predictions of Hartree–Fock and perturbation theory. The consequences of our findings are discussed.
Electronic structure of the disordered-local-moment state of face-centered-cubic iron
Authors: Shelton W. A. , Pinski F. J. , Stocks G. M. , Nicholson D. M. , Gyorffy B. L.
Published: July 2002

We calculate the electronic structure of fcc iron in the disordered-local-moment state using the self-consistent Korringa–Kohn–Rostoker coherent-potential approximation (KKR-CPA). As the volume is reduced the moments decrease and, as many previous calculations have shown, there is also a change from ferromagnetic to antiferromagnetic correlations between local moments. In this paper, we show that there is a corresponding change from split to common band behavior of the electronic states and suggest that this is important in understanding the changing nature of magnetic interactions.
Open problems in Monte Carlo renormalization group: Application to critical phenomena (invited)
Authors: Gupta Rajan
Published: July 2002

The Monte Carlo renormalization group (MCRG) methods and the underlying theory is reviewed. The Gupta–Cordery improved MCRG method is described and compared with the standard one. The emphasis is on the progress made in understanding the truncation errors in the linearized transformation matrix and on open problems. The problem of deteriorating exponents with long-range transformations is highlighted. Lastly, some of the existing methods for calculating the renormalized Hamiltonian are reviewed and evaluated.
Reentrant spin-glass properties of a-(FexCr1−x)75P15C10
Authors: Mangin P. , Boumazouza D. , Tete C. , Erwin R. W. , Rhyne J. J.
Published: July 2002

The magnetic excitations and instantaneous spatial correlations have been studied in amorphous (FexCr1−x)75P15C10 using neutron inelastic scattering and small-angle neutron scattering (SANS). We report here the results for the sample with x=0.7, which is in the reentrant spin-glass region (RSG) of the magnetic phase diagram. As in other materials displaying RSG properties, we find conventional spin-wave behavior for temperatures down to about half the Curie temperature (TC=134 K), but decreasing excitation energies and lifetimes as the temperature is further lowered. We have studied the critical scattering near TC with SANS, and find that the transverse correlation length ‘‘diverges’’ provided that the data analysis includes the longitudinal fluctuations. The longitudinal correlation length decreases rapidly below TC as expected in a conventional ferromagnet, and the amplitudes for transverse and longitudinal scattering have the expected 2:1 ratio. The RSG temperature regime is characterized by the appearance of a Lorentzian-squared term in the scattering function with a ‘‘nondiverging’’ correlation length, and an amplitude proportional to the RSG order parameter.
Magnetic behavior of the Co2−xZnxTiO4 and Co2SnO4 systems
Authors: Srivastava J. K. , Ramakrishnan S. , Marathe V. R. , Chandra G. , Vijayaraghavan R. , Kulkarni J. A. , Darshane V. S. , Singh S.
Published: July 2002

Our ac susceptibility (χ) measurements, carried out between 1.7 and 100 K, show five χ peaks, signaling five transition temperatures, in the disordered frustrated spinel ferrite Co2TiO4. This result, in conjunction with the replica symmetric mean field theory of vector spin glasses and earlier magnetization and neutron diffraction studies, indicates a separate freezing of A- and B-site spins. To our knowledge, such a phenomenon has not been observed before. Co2SnO4 and Co1.2Zn0.8TiO4 χ measurements, where three and one χ peaks are respectively observed, support this picture.
Effect of Mn on the collapse of ‘‘ferromagnetic’’ order in melt-spun Fe90Zr10 amorphous alloys (abstract)
Authors: Nicolaides G. K. , Hadjipanayis G. C. , Rao K. V.
Published: July 2002

It is well known that amorphous Fe-rich binary Fe-Zr alloys exhibit two magnetic transitions as a function of decreasing temperatures. For example, it is found that an amorphous melt-spun Fe90Zr10 alloy has a ‘‘ferromagnetic’’ transition at about 230 K which is then followed at low temperatures by a loss of long-range order into a spin-glass-like state at around 12 K. The question arises as to the role of Zr in the unusual properties of binary amorphous alloys containing as much as 90 at. % Fe. In order to gain further insight into the above, we have carried out low-field ac susceptibility as well as dc magnetization studies in both low and high applied fields on melt-spun Fe90−xMnxZr10 alloys for 0≤x≤22 at. % Mn. The amorphicity of all the alloys were checked by using x-ray techniques. On substituting Fe with Mn, initially the Curie temperature is unaffected but the spin-freezing temperature Tfg decreases. At higher concentrations of Mn (above 10 at. %) TC decreases at the rate of 30 K/at. % Mn while Tsg begins to increase to temperatures above 50 K as determined from the peak in the quadrature component of the ac susceptibility. Thus the magnetic properties of Fe-Mn-Zr alloys appear to be mainly determined by the exchange coupling among Fe, Fe-Mn, and Mn-Mn atoms with Zr playing the role of simple glass-forming element. Detailed hysteretic loop studies will also be presented. Finally, we shall compare the above results with those obtained on substituting Fe with Ni and a light rare-earth Pr.
Magnetic behavior of diluted lanthanoid-pnictide systems
Authors: Schneemeyer L. F. , van Dover R. B. , Gyorgy E. M.
Published: July 2002

We describe a new class of low-carrier-density magnetic materials based on lanthanide-substituted scandium and yttrium pnictides. In general, these III-V compounds have energy gaps in the vicinty of 1 eV, and like most of the lanthanide pnictides, form in the B1 (rocksalt) structure. Substitution of rare earths for Y or Sc to form solid solutions is readily achieved. For example, we have produced GdxY1−xN by reactive magnetron cosputtering, and obtained epitaxial growth on sapphire substrates resulting in high-quality single-crystal thin films. These films exhibit moderately low carrier densities and high mobilities, and have interesting magnetic properties at low temperatures. In this paper we present a preliminary look at some of the properties of these materials.