bluuebunny/crossref_metadata_2025 huggingface dataset:
Magnetostatic modes and chaos in yttrium iron garnet films
Authors: Carroll T. L. , Pecora L. M. , Rachford F. J.
Published: July 2002

Nonlinear interactions in yttrium iron garnet cause complex, low-frequency signals seen during ferromagnetic-resonance experiments. Several methods from nonlinear dynamics have been used to measure quantities such as dimensions, Lyapunov exponents, and others, to characterize complex behavior that is measured by ferromagnetic resonance experiments. It is found that these quantities may be more useful in understanding the interactions in yttrium iron garnet than more commonly measured quantities such as oscillation frequency. Very simple numerical models are also used to suggest which quantities are most important in characterizing these spin-wave interactions.
Oriented aluminum nitride thin films deposited by pulsed-laser ablation
Authors: Norton M. Grant , Kotula Paul G. , Carter C. Barry
Published: July 2002

Single-phase aluminum nitride thin films with preferred crystallographic orientations have been grown on single-crystal sapphire by pulsed-laser ablation. The orientation of the films was found to be determined by the atmosphere and the nitrogen pressure during deposition and the substrate temperature. The films were examined by x-ray diffraction, and scanning electron microscopy.
Effect of (NH4)2Sx treatment on the passivation of GaP surface
Authors: Lee Jong-Lam , Wei Long , Tanigawa Shoichiro , Oigawa Haruhiro , Nannichi Yasuo
Published: July 2002

We applied slow positrons to both as-etched GaP and (NH4)2Sx-treated GaP. The results show that the surface of as-etched GaP is active for the adsorption of oxygen atoms when the etched surface was exposed to air for several minutes before the measurement. On the other hand, the monolayer of chemisorbed sulfur in (NH4)2Sx-treated GaP is effective to protect the clean surface from the adsorption of the oxygen atoms. The mean diffusion length of positrons in the etched GaP is shorter than that in (NH4)2Sx-treated GaP. This suggests that the centers for the positron trapping, such as Ga vacancies VGa and/or VGa-related complexes, are created by the adsorption of oxygen atoms.
Low substrate temperature molecular beam epitaxial growth and the critical layer thickness of InGaAs grown on GaAs
Authors: Elman B. , Koteles Emil S. , Melman P. , Ostreicher K. , Sung C.
Published: July 2002

We report on the critical layer thickness of InxGa1−xAs on GaAs grown at low substrate temperatures in a wide range of indium compositions. Compared with ordinary growth conditions, the transition between pseudomorphic and relaxed regions (in the epilayer thickness versus x plane) occurred at higher indium compositions when the growth temperature was lowered. An increase in critical thicknesses for pseudomorphic growth by at least a factor of seven for alloy compositions with less than 45% indium was observed. This was determined by low temperature photoluminescence spectroscopy and transmission electron microscopy measurements on single quantum wells.
Profile of titanium lines produced by excimer laser direct writing on lithium niobate
Authors: Lavoie C. , Meunier M. , Boivin S. , Izquierdo R. , Desjardins P.
Published: July 2002

The profile of titanium (Ti) lines produced by KrF excimer laser direct writing on lithium niobate (LiNbO3) has been investigated in detail since it is critical in the fabrication of Ti in-diffused LiNbO3 optical waveguides. Lines written at speeds varying from 0.5 to 10 μm/s have typical thicknesses and linewidths varying from 10 to 185 nm and from 2 to 24 μm, respectively. At a low power density E, the maximum thickness t is proportional to the number of photons or the power density. Increasing E allows a sufficient heating, which leads to the diffusion of Ti into LiNbO3, resulting in a sharp decrease of the thickness in the middle of the deposited line.
Experimental determination of the upper critical field of epitaxially grown thin films of YBa2Cu3O7−δ down to He temperature
Authors: Wördenweber R. , Abd-El-Hamed M. O. , Schneider J. , Laborde O.
Published: July 2002

The upper critical field of YBa2(Cu1−xFex)3O7−δ with x=0 and 0.05 is determined over the whole temperature range from 4.2 K to Tc. The data behave according to the theory of Werthamer, Helfand, and Hohenberg [N. R. Werthamer, E. Helfand, and P. C. Hohenberg, Phys. Rev. 147, 295 (1966)]. However, at low temperatures the upper critical field is larger than expected from the original expressions of Werthamer and co-workers. Generalized equations, which take into account the anisotropy of the Fermi surface, yield values for the upper critical field, which are in excellent agreement with the experimental data.
Photoluminescence characterization of InP surface reactive ion etched by a gas mixture of ethane and hydrogen
Authors: Ohtsuka K. , Ohishi T. , Abe Y. , Sugimoto H. , Matsui T.
Published: July 2002

InP crystals were etched by reactive ion etching (RIE) with gas mixture of ethane and hydrogen (C2H6/H2), and etching damages were characterized by photoluminescence (PL) measurements of near-edge and defect-related emissions. Near-edge PL emission intensities after RIE were equal to or larger than those before RIE, except for the samples etched for 50 min. The damage introduced by RIE was restricted to the very-near-surface region which can be removed by HF treatment. The peak energy of defect-related 1.1-eV deep emission bands shifted toward the lower-energy side for the crystals with etching damages at the surface. The peak shift is attributable to the increase of defect complexes such as P-vacancy–P-interstitial or P-vacancy–In-vacancy.
A phase map for sputter deposited niobium oxides
Authors: Lee Ray C. , Aita Carolyn Rubin
Published: July 2002

A Nb target was sputtered in radio frequency (rf) Ar/O2 and Ne/O2 discharges, and films were grown on unheated fused silica, 〈111〉-cut Si, and carbon ribbon. The transition from Nb metal to niobia film growth was studied as a function of three independent process parameters: cathode voltage, gas O2 content, and rare gas type. On the basis of x-ray diffraction results, resistivity, optical transmission, refractive index, Nb:O ratio, and infrared absorption characteristics, the following phases were identified in the films: bcc Nb, NbO, NbO2, x-niobia, amorphous niobia, microcrystalline niobia, and crystalline niobia (where niobia=Nb2O5−x with 0≤x≤0.2). In situ optical spectrometry of the discharge was used to monitor the emission intensity I(λ) of four radiative electronic transitions of the neutral excited Nb atom to ground state (λ=5344, 5079, 4101, and 4059 Å). Changes in I(λ) and the growth rate was used to (1) determine the set of process parameters at which target surface oxidation occurred, and (2) estimate the fractional flux of atomic Nb and Nb bonded to O in an unspecified molecular form (Nb-oxide) incident on the substrate. Film structure was found to depend to some extent upon this fractional flux. A phase map was constructed in which film structure and the Nb and Nb-oxide fractional flux were graphed onto process parameter space, demonstrating the equivalent effect of different sets of process parameters.
Quantum mechanical correction on capacitance-voltage characteristics of narrow gap semiconductors
Authors: Yang M. J. , Yang C. H.
Published: July 2002

We show that for narrow band-gap semiconductors, the doping concentration deduced from capacitance-voltage measurements can be substantially underestimated due to surface quantization effect. While our derivation can be applied to all materials, detailed accounts on p-type Hg0.788Cd0.212Te are given as an example. We found that for a practical doping range, 1×1015 cm−3 to 1×1017 cm−3, the doping level can be underestimated by 53% to 173%, respectively.
The isotope effect of boron implantation in silicon simulated
Authors: Tsatis Demetre E.
Published: July 2002

The implantation profile of 10B and 11B ions into 28Si, 29Si and 30Si, respectively, have been studied by using the TRIM-89 code at the energy range between 50 and 250 keV. It is found that the presence of the least abundant silicon isotope 30Si, in the target material, is causing the biggest broadening to the implantation profile.
Frequency dependence of transconductance on deep traps in GaAs metal semiconductor field-effect transistors
Authors: Zhao Jian H. , Tang Pin F. , Hwang Robert , Chang Steven
Published: July 2002

A transconductance spectroscopy method is introduced through computer modeling which provides an easy way to the determination of energy levels of surface states and bulk traps in a GaAs metal semiconductor field-effect transistor. It is shown that in the transconductance spectrum each trap will result in a peak at a frequency which is equal to the characteristic frequency of the trap. It is suggested that peaks due to surface states can be distinguished from those due to bulk traps in the gated channel region by the dependence of the surface-state peak height on the gate-source reverse bias. It is found that previous experimental reports of transconductance dependence on temperature and surface leakage current can be explained by the model developed in this study.
Mechanism of phase-shifted distributed-feedback laser with linearly chirped grating for stable-mode operation
Authors: Zhou Ping , Lee G. S.
Published: July 2002

A phase-shifted (PS) distributed-feedback (DFB) laser with linearly chirped grating (CG) was analyzed using the coupled-mode equations and rate equations. It was found that the mode instability of a DFB laser was caused by both the lasing-mode movement and the deterioration of the effective reflectivity spectrum of the corrugated-grating waveguide caused by the nonuniform carrier distribution under the injection. By suitable arrangement of the chirped factor of the PS-CG-DFB laser and the phase-shift value, PS-CG-DFB laser can overcome the effective reflectivity spectrum-deterioration problem and make the mode more stable under injection.
Microvoid nucleation at the interface between a thin film and a substrate in fatigue
Authors: Qin S. , Fan H. , Mura T.
Published: July 2002

In the present paper, a dislocation dipole model is employed to simulate the nucleation of microvoids at the interface between a thin film and a substrate. In this model, the accumulation of dislocation dipoles plays a major role in the formation of a microvoid. The total free energy of the system increases with the fatigue cycle number due to the increase in elastic strain energy. It is shown that there exists a critical fatigue cycle number beyond which the initial state of dislocation dipole accumulation becomes energetically unstable, and the energy of this state will be released by the formation of a microvoid at the interface. The study can provide not only the S–N curves for the initiation but also their dependence on material parameters such as the thickness of the film, the grain size of the substrate, the shear moduli ratio, etc. The coalescence of those microvoids is expected to be one of the mechanisms of delamination of the thin film from its substrate.
Disorder-induced band-tailing effects on deep levels in semiconductors
Authors: Teate A. A. , Halder N. C.
Published: July 2002

We have investigated the effects of disorder-induced band tailing on deep levels in compound semiconducting alloys, such as GaAs and AlxGa1−xAs. In particular, we have eliminated the assumption of Gaussian broadening of the defect density of states proposed earlier by others on the basis of the central-limit theorem. The expressions derived for the transient capacitance in the presence of the disorder-induced band tailing are quite different from previously published results and indicate that the form of the broadening function is quite sensitive to, and should closely reflect, the underlying physical environment. We applied this theory to the investigation of the deep-level transient spectra (DLTS) and isothermal capacitance transient spectra (ICTS) in GaAs and AlxGa1−xAs. Our results indicate that standard experimental measurements with DLTS and ICTS, in general, can underestimate the activation energy, capture cross section, etc., even in the case of weak disorder.
Influence of deposition rate on the magnetic, crystalline, and recording properties of CoCrTa/Cr media
Authors: Miller M. S. , Walber J. P. , Erskine H. F. , Hagen B. M. , Hsu Y. , Judy J. H. , Sivertsen J. M. , Speliotis D. E.
Published: July 2002

The effect of magnetic layer deposition rate on longitudinal media’s magnetic, crystalline, and recording properties was studied. Slower deposition rates were found to produce a systematic reduction in media transition noise. X-ray diffraction and torque magnetometer data indicated that as the deposition rate was slowed, the out-of-plane anisotropy component of the media increased. Slower deposition rates were also found to increase media saturation magnetization. Increased media signal-to-noise ratios were observed when higher process temperatures were used in conjunction with slower rates. These results are discussed in terms of recent theories which have linked phase segregation and out-of-plane crystalline anisotropy with media magnetic and recording properties.
Photoionization cross sections in resonance ionization mass spectrometry of sputtered metal atoms: Applications to material analysis
Authors: Gobert O. , Gibert T. , Dubreuil B. , Gelin P. , Debrun J. L.
Published: July 2002

(1+1) resonant multiphoton ionization of several metal atoms was investigated in the 285–301-nm-wavelength range. Fe, Mg, Cr, Ti, and Ni free atoms were produced using Ar+-ion sputtering of different metal samples in ultrahigh-vacuum conditions. The photoionization yields, measured as function of the laser fluence, exhibit saturation or near saturation at the highest laser energy density available in the experiment (100 mJ/cm2). From these measurements the ionization cross sections of the intermediate excited states are deduced, assuming saturation of the excitation step. In this way values ranging between 0.7 and 4×10−17 cm2 are obtained. One can take advantage of the relatively large cross sections to detect these sputtered metal atoms by resonance ionization mass spectroscopy with great sensitivity. Some examples are given, demonstrating, on a single-laser-shot basis, the real analyses of Mg and Ti atoms in materials at the ppm level.
Coercivity of porous acicular particles
Authors: Chang Ching-Ray , Shyu J. P.
Published: July 2002

It has been suggested that the porosity in the magnetic particle has the crucial effect upon observed low coercivity, as compared with predictions of single-domain theory. However, the influence of the inner pores was never theoretically analyzed. When interactions among the pores are considered, we found that the coercivity of a single-domain particle depends on not only the porosity but also the number of pores. Moreover, in some cases the porosity increases the coercive force, in others it decreases it. When the pore number is large, the relationship between coercive force and porosity is quite linear. The magnetization of the particle is always decreasing as porosity increases. It was also found that the oblique angle between the inner pore and magnetic particle results in the decrease of the coercivity. To increase the coercivity, it is concluded that the pore shape is more important than the reduction of the porosity and the alignment of the pore.
Resonant tunneling of holes in Si/GexSi1−x
Authors: Fu Y. , Chen Q. , Willander M.
Published: July 2002

The compressional strain in GexSi1−x grown on Si moves the light-hole (LH) band down and the heavy-hole (HH) band up, while the tensile strain in Si grown on GexSi1−x moves the LH band up and the HH band down. In the tunneling structure of Si/GexSi1−x grown on a Si substrate with a GexSi1−x or Si buffer layer, the band offsets of LH and HH are then changed depending on the strain in Si/GexSi1−x, which is influenced by the lattice relaxation of the buffer layer. In this work the Fermi level Ef of the tunneling structure is investigated from the energy band structure calculations to provide information for tunneling current calculations and peak identification in comparison with experimental I-V spectra. When a Si buffer layer is used, only the HH band of the GexSi1−x spacer is found to be filled so that the tunneling current is HH characteristic. With a GexSi1−x buffer layer both LH and HH contribute to the total tunneling current. The effective mass approximation is also investigated for Si/GexSi1−x tunneling structures and a quasiparticle (HH, LH, and the spin-orbital splitoff) tunneling picture is justified for theoretical analysis.
Electron beam emittance growth in thin foils: A betatron function analysis
Authors: Reid Max B.
Published: July 2002

The emittance of an electron beam increases due to multiple scattering when passing through one or more thin foils. The effect of a given foil on a beam’s emittance is dependent on whether the beam is diverging, converging, or at a waist. A method for calculating the growth in emittance using betatron functions is presented. The technique provides a full description of the beam in phase space after a thin scatterer.
Photoreflectance studies in CuGaS2 single crystals
Authors: Shirakata S. , Isomura S.
Published: July 2002

Photoreflectance (PR) measurements have been performed near the fundamental absorption edge of CuGaS2 single crystals grown by an iodine-transport method. The PR spectra at room temperature are analyzed as the superposition of exciton and band-to-band transition. The exciton transition energies at 290 and 77 K are obtained to be 2.463 and 2.503 eV, respectively. The quality of CuGaS2 crystals grown with different amounts of iodine is characterized with respect to energies and broadening of the PR spectra.
Limiting density distribution for charged particle beams in free space
Authors: O’Connell James S.
Published: July 2002

An analytic solution is given to the Vlasov equation describing the time evolution of an axially symmetric beam of charged particles spreading radially under the influence of self fields. The marginal densities as a function of radius and of radial velocity are found to be flat out to the expanding edges of the beam. This solution is shown to have the maximum entropy for a given phase-space area. Thus an arbitrary initial distribution will evolve toward this solution as a limiting distribution.
Theoretical and experimental investigation of the drift velocity in AlGaAs/GaAs heterostructures
Authors: Zandler G. , Kiener C. , Boxleitner W. , Vass E. , Wirner C. , Gornik E. , Weimann G.
Published: July 2002

The drift velocity of hot electrons in AlGaAs/GaAs heterostructures is measured at different temperatures by a pulsed I-V technique up to electric fields of 1.2 kV/cm. The experimental results are compared with theoretical drift velocities deduced from the Boltzmann integral equation and a balance equation method. The calculations are carried out with selfconsistent and Stern–Howard wave functions taking into account polar optical phonon and ionized impurity scattering as well as electron-electron collisions. At low field strengths both theoretical methods lead to drift velocities which are in good agreement with the experimental data. It is shown that for higher lattice temperatures and higher electric field strengths intersubband scattering has to be taken into account in the theoretical models.
Scattering mechanisms in inverted AlGaAs-GaAs heterostructures studied by magnetotransport measurements
Authors: Rauch W. , Gornik E. , Weimann G. , Schlapp W.
Published: July 2002

We determined the single particle relaxation time τs and the classical transport scattering time τt out of Shubnikov-de Haas (SdH) measurements at a GaAs-AlGaAs-GaAs double heterostructure consisting of a normal and an inverted interface. As a result we find that even in inverted heterostructures the classical scattering time τt is an order of magnitude larger than the single particle relaxation time τs. From a comparison with theoretical calculations including scattering from remote impurities, interface charges, and interface roughness, we conclude that the mobility in inverted heterostructures at low temperatures is dominated by Coulomb scattering from remote dopants and interface charges in the barrier, rather than interface roughness scattering. Nevertheless, the mobility of the inverted interface turns out to be significantly lower than that of a normal interface.
The effect of liquid-phase sintering on the properties of Pr6O11-based ZnO varistors
Authors: Alles Aldo B. , Burdick Vernon L.
Published: July 2002

Conventionally batched varistors in the ZnO–Co3O4–Pr6O11 system that were sintered at or above 1280 °C exhibited a sharp increase in the average breakdown voltage per grain boundary. In these samples, barrier heights and donor concentration values, derived from capacitance-voltage analysis, exhibited sharp changes at the same soaking temperature. At or above 1280 °C, grain growth in this system proceeds with the assistance of an eutectic liquid. The improvement of the distribution of Pr6O11, by precipitation of Pr(OH)3 during batching, resulted in varistors markedly more insensitive to firing temperature than conventionally batched ones. The presence of a liquid phase, at least during grain growth, results in an efficient distribution of grain boundary materials and dopants in general. Suitable chemisorbed gases along the grain boundaries are believed to be responsible for the formation of interface states. Segregated materials appeared to provide for enhanced transport of gaseous species along the grain boundaries. The need for the addition of oxides with large ionic-radius cations, i.e., varistor-forming oxides such as bismuth, barium, praseodymium, or lanthanum oxide, to varistor compositions is explained within this context.
The effect of aging at 500 °C on Nb-containing Nd-Fe-B magnets
Authors: Freeman R. J. , Swain H. , Harris I. R.
Published: July 2002

The aging behaviors of Nd16.4Fe75.7B7.9, Nd16Fe76.3Nb0.3B7.4, and Nd14.5Dy1.5Fe76Nb1B7 magnets were investigated. The magnets were quenched and then aged at 500 °C to establish whether recovery of coercivity was possible below the melting point of the grain boundary. The samples were cooled and measured magnetically after 10- or 20-min intervals before being heated again for another interval. After aging at 500 °C for 55 min there was a dramatic increase in coercivity in the Nd-Dy-Fe-Nb-B samples, whereas the coercivity of the Nd-Fe-B samples remained unaltered. The results from thermomagnetic analysis on Nd-Dy-Fe-Nb-B show that an extra ferromagnetic phase is present in the magnets that had been aged for over 55 min and in the magnets that had full magnetic properties, but not in the quenched magnets. The Nd-Fe-B samples did not show any additional ferromagnetic phase. The experiments were repeated with Nd-Fe-Nb-B magnets and the results followed the same trend to those observed in the Nd-Dy-Fe-Nb-B magnets. The difference in coercivity between the aged and the initial-state magnets, for all types, was recovered upon heating at 650 °C.
Magnetic characterization of oxidized Fe-Nd alloys
Authors: Sinnecker E. H. C. P. , Gama S. , Ribeiro C. A.
Published: July 2002

In this work results of oxidation experiments on Fe-Nd alloys are presented. Samples were prepared by melting the metals and Nd oxide, and by melting the metals, stabilizing the alloys through long heat treatments, and oxidizing them in low-oxygen partial pressures. Two mechanisms of oxidation are observed, one with precipitation of a fine Nd2O3 dispersion in the alloy matrix, with simultaneous displacement of the phase compositions to Fe-rich values. Eventually, pure Fe striae are formed. The second mechanism corresponds to the direct formation of a mixed oxide and Nd2O3.
Laves-phase pseudobinaries A(Fe1−x
B
x)2 (A=Zr, Hf; B=Al, Si): Some structural and magnetic properties
Authors: Zamora S. , da Silva C. M. , Schmidt J. E. , Livi F. P. , Gomes A. A.
Published: July 2002

The lattice parameters and the saturation magnetization are measured for the series of intermetallic compounds A(Fe,B)2, A=Zr, Hf and B=Si and Al, with concentrations less than 15%. The magnetization measurements and the lattice parameter behavior are qualitatively discussed.
Sensitivity limits to ferrimagnetic Faraday effect magnetic field sensors
Authors: Deeter M. N. , Rose A. H. , Day G. W. , Samuelson S.
Published: July 2002

In general, the sensitivity of ferrimagnetic Faraday effect magnetic field sensors is a function of both the crystal geometry and composition. The geometrical dependence of the sensitivity in nonellipsoidal crystals, such as cylinders, is complicated by their spatially nonuniform demagnetizing factors. We compare sensitivity data obtained from a variety of cylindrical iron garnet samples with models which predict the effective demagnetizing factor Neff as a function of the length-to-diameter ratio. With respect to composition, we present experimental results of sensitivity vs diamagnetic substitution (x) in the iron garnet series Y3Fe5−xGaxO12. As expected, the sensitivity rises sharply as x approaches the compositional compensation point.
Spin-polarized carrier populations in diluted magnetic semiconductor quantum well structures (abstract)
Authors: Jonker B. T. , Chou W. C. , Petrou A. , Warnock J. , Prinz G. A.
Published: July 2002

Diluted magnetic semiconductors (DMS) offer the opportunity to significantly alter heterojunction band offsets via an applied magnetic field due to the large Zeeman splittings (enhanced g-factors) they exhibit. We have previously reported field-dependent spatial spin segregation of holes in DMS quantum well structures1,2 which resulted from the small band offset and large spin splitting exhibited by the valence band. We report here the growth of tailored Zn1−xFexSe/ZnSe quantum well structures in which both electrons and holes are spatially segregated according to their spin, resulting in spin-polarized carrier populations in the barriers and wells: the spin-down carriers are localized in the Zn1−xFexSe barriers, while the spin-up carriers are localized in the wells. Both single and multiple quantum well samples were grown by molecular-beam epitaxy on GaAs(001) substrates with 100 Å barriers and wells. The heavy-hole excitonic transitions were studied with magnetoreflectivity at T=4.2 K and fields up to 8 T. The magnetoreflectivity data show that both (−3/2→−1/2) and (3/2→1/2) excitonic transitions are of equal intensity and spatially direct (type I), with the former showing the strong field dependence expected for localization in the magnetically active barriers.
Increase in coercivity of Fe/Ti multilayered films by Cr addition into Ti layers
Authors: Nakagawa Shigeki , Naoe Masahiko
Published: July 2002

Fe/Ti multilayered films prepared by plasma-free sputtering revealed high coercivity. The effect of elevating substrate temperature and adding Zr and Cr into Fe and Ti layers, respectively, have been examined to increase the coercivity Hc. The elevation of substrate temperature to 200–400 °C did not bring a significant increase in Hc. Addition of Zr into Fe layers caused a soft magnetism because of the small Fe grain size. On the other hand, addition of Cr into Ti layers revealed a significant increase in Hc especially for the films with small Fe thickness lFe. Although the magnetization of Fe/Ti multilayered films with lFe of about 16 Å was almost zero, that of Fe layers in Fe/Ti90Cr10 multilayered films was as large as 14 kG with a high Hc of about 400 Oe. X-ray diffractometry (XRD) implies that the small Fe grain size and the magnetic interaction between atoms at the interface may be one of the origins of such high Hc.
Magnetic properties of the sintered magnets produced from a Nd-Fe-B-Cu-type material
Authors: Kianvash A. , Harris I. R.
Published: July 2002

The magnetic properties of Nd17Fe76.5B5Cu1.5-type sintered magnets, produced using a combination of hydrogen decrepitation and milling, have been investigated. An isothermal anneal or a step anneal, both performed after homogenization, resulted in a marked improvement of magnetic properties of the sintered magnets. Thermomagnetic analysis (TMA) of the sintered magnets showed that, in addition to a matrix phase with a Tc = 314 ± 5 °C, there was another ferromagnetic phase with a Tc = 54 ± 5 °C. The microstructural investigations showed a considerable amount of free α-iron in the cast material, whereas no free iron was observed in the microstructure of the sintered magnets. However in very isolated areas within the sintered magnets, a Nd-Fe phase with Fe/Nd∼8 was identified (probably Nd2Fe17-type phase). The observation of this phase was consistent with results of TMA and the possible role of this phase in coercivity behavior is discussed.
Magnetic field alignability of hot-rolled anisotropic Nd-Fe-B-Cu powders
Authors: Mukai T. , Inaguma T. , Okazaki Y. , Sakamoto H.
Published: July 2002

We have investigated alignability of anisotropic Nd-Fe-B powders in a magnetic field when they are resin bonded by compression moulding. A high-energy anisotropic powder of Cu-added Nd-Fe-B alloys, which was fabricated by packed rolling of melt-spun ribbons, is used for the present study. The result is compared with the alignability of conventional 2:17 type Sm-Co powder. For a Nd-Fe-B-Cu powder (iHc = 16 kOe), 90% of the saturated Br value was obtained at an aligning field as low as 2 kOe, whereas for a Sm-Co powder (iHc = 12 kOe), an aligning field of 13 kOe was required to obtain the 90% value. The good alignability of the Nd-Fe-B-Cu powder is attributed to a steep rise in the initial magnetization curve. It benefits radial orientation of the powder in ring magnets, for which limitations of the aligning field exist depending upon the size of the magnet. A maximum energy product of 15 MGOe has been obtained for radially oriented Nd-Fe-B-Cu bonded magnets.
High coercivity melt-spun Nd10–11.5Fe82–84B2–5M1–6 alloys (M=Ti/V/Mo/Al) (abstract)
Authors: Lin C. H. , Chu T. Y. , Chang W. C. , Wu C. D. , Huang S. H. , Chin T. S.
Published: July 2002

In an alloy design to precipitate the hard Nd2Fe14B (2-14-1) in the NdFe11M (1-12 phase, M is one of Ti/V/Mo/Al) matrix, different ratios of the 2-14-1 composition were added into the 1-12 compositions and prepared by melt spinning. It resulted in high-coercivity Nd-Fe-B-M alloys (M is Ti/V/Mo/Al) with Nd and B composition less than the stoichiometric 2-14-1 compound, yet with promising intrinsic coercivity (iHc) of up to 12 kOe after suitable annealing. XRD analyses showed that for the alloys with higher iron lower in both Nd and B, the matrix is 1-12 and alpha-iron, while for the alloys with higher Nd and B, the 2-14-1 is competitive with other phases. The iHc vs temperature fitting of a Nd10Fe83.1B2.7Ti4.2 alloy (iHc=80 kA/m at 293 K) shows weak pinning, while that of a Nd10.8Fe82.9B4.4Ti1.9 alloy (iHc=900 kA/m at 293 K) shows strong pinning.
Anomalies in the temperature dependence of Faraday rotation on yttrium iron garnets doped with Sn, Zr, or Sb
Authors: D’Orazio F. , Giammaria F. , Lucari F.
Published: July 2002

Faraday rotation (FR) measurements on three thin single crystalline samples of yttrium iron garnet doped with Sn, Zr, and Sb as a function of temperature in the near infrared region show a monotonic variation of the magneto-optical signal as the temperature is decreased from 300 to about 50 K. At this point the FR signal levels off. Moreover, the slope of the plot for the sample, doped with Sn, changes sign below this temperature, at particular wavelengths. An explanation of the observed phenomena is given in terms of the energy levels of the Fe2+ ions in the different sites of the crystal and the temperature dependence of their populations caused by the relative orientation between the local symmetry axis of the specific site and the direction of the sample magnetization. Hysteresis loops of the Faraday rotation as a function of applied magnetic field have been also measured showing the presence of a remanence of the sample magnetization.
Anisotropy of grain-oriented steel sheet under various elliptical field conditions
Authors: Salz W. , Hempel K. A.
Published: July 2002

We investigated the magnetic behavior of grain-oriented steel sheet under various elliptical field conditions. The measurements show an additional anisotropy of the material properties depending on the direction of the elliptic rotation. We ascribe these phenomena to the different symmetries of the crystal anisotropy energy and of the ellipsoidal fields.
Spin glass-like behavior in Fe-doped Bi4Sr8Cu5O19+x insulating perovskite
Authors: Caldés M. T. , Fuertes A. , Bruna Ll. , Obradors X. , Fontcuberta J. , Martinez B. , Perez F.
Published: July 2002

Polycrystalline samples of the tubular phase Bi4Sr8Cu5O19+x with Fe ions substituting the Cu positions have been prepared up to a maximum content of 2 Fe ions per unit formula. The electrical and magnetic properties of these oxides have been examined and it is shown that they are insulating and present a complex magnetic behavior. It is found that the Fe ions have a localized magnetic moment displaying a Curie–Weiss law at high temperatures while below T≊100 K antiferromagnetic correlations are detected. From the evaluation of the effective paramagnetic moment and its composition dependence it is deduced that Fe doping induces a paramagnetic moment in some Cu ions which then contribute also to the temperature dependent paramagnetism. Finally, at lower temperatures (T<25 K) a susceptibility peak is observed signaling a freezing of the magnetic moments. We suggest a spin-glass behavior associated either to a clustering of Fe ions or to the development of correlated domains interacting through the strongly correlated copper ions. We point out that the weak sensitivity of the resistivity on the Fe concentration gives further support to the hypothesis of some Fe clustering within the tubular crystal structure.
Universality classes of dynamical behavior (abstract)
Authors: Liu Jian-Min , Müller Gerhard
Published: July 2002

In studies of dynamic correlation functions the focus is, in general, on their long-time asymptotic behavior and the singularity structure of the associated spectral densities. It turns out that the analysis of the same dynamic correlation functions from a quite different perspective is equally useful and revealing. The focus of our study is on the properties of spectral densities at high frequencies, specifically their decay law, expressible asΦ0■ω■ ∼exp■ − ω2■λ■, in terms of a characteristic exponent λ. That decay law governs the growth rate of the sequence of recurrents which determine the relaxation function in the continued-fraction representation. The value of λ contains valuable information on the underlying dynamical processes taking place in the system, which, in some sense, is complementary to that inferred from the singularity structure of spectral densities. A detailed study of the dynamics of various quantum and classical spin models has prompted us to introduce the concept of ‘‘universality class’’ for a classification of dynamical behavior on the basis of the characteristic exponent λ. For the equivalent-neighbor XYZ model1 we are able to demonstrate four different prototype universality classes: λ=0 (compact support), λ=1 (Gaussian decay), λ=2 (exponential decay), λ=3 (stretched exponential decay), which can be interpreted in terms of basic notions of classical dynamics. Finally, we present the exact T=∞ dynamic correlation functions for a two-sublattice Heisenberg antiferromagnet with uniform intersublattice interaction and zero intrasublattice interaction.
Rietveld analysis of x-ray powder diffraction patterns for the new SmFe10Mo2Nx nitride compound
Authors: Psycharis V. , Anagnostou M. , Christides C. , Niarchos D.
Published: July 2002

Considerable improvement of the magnetic properties has been achieved by nitrogen absorption in the RFe10Mo2 compounds with ThMn12-type structure. A lattice expansion has been observed (a=8.6781, c=4.8531 Å for the nitride and a=8.5869, c=4.8002 Å for the nitrogen-free sample) from N2 absorption and a determination of the displaced Sm, Fe, and Mo positions has been achieved from Rietveld analysis for the SmFe10Mo2Nx compound. This structure determination provides some evidence for the site occupation of the nitrogen atoms in the tetragonal ThMn12-type structure. Measurements of an oriented powder sample at 295 K show that the easy magnetization direction is in the (a,b) plane.
Effects of Cr substitution of the intrinsic properties of the Nd14Fe78C8 compound (abstract)
Authors: Xing Feng , Liu Zun-Xiao , Ho Wen-Wang
Published: July 2002

The unusual behavior of a decrease of crystal cell volume V with Cr concentration in Nd14Fe78−xCrxC8 compounds is observed and explained. The saturation magnetization σs of the compounds has a marked drop with increasing Cr content. This is due to the Cr atoms probably have a preference for occupation on 8j1 site or/and 16k2 site, and antiparallel alignment of the moments between Cr and Fe atoms, leading to considerable decrease of Tc. The anisotropy field HA at room temperature decreases at a rate of about 10 kOe/Cr atoms, similar to the one observed in Nd2Fe12Cr2B. The temperature dependence of magnetizations in the bulk, nonaligned sample of Nd14Fe63Cr15C8 at applied fields of 1, 3, and 5 kOe, respectively, were measured from 1.5 to 300 K and back in separate runs. The two jumps in the virgin run were explained. The coercive forces iHc are found to increase with Cr concentration and reach a maximum at x=15, and consequentially decrease. The temperature dependence of iHc for Nd14Fe63Cr15C8 changes of the logarithm of iHc with T is nearly linear. Such a linear dependence may be explained by the thermal activation process of domain walls.
Effect of magnetic dilution on magnetic ordering in NipMg1−pO
Authors: Feng Z. , Babu V. Suresh , Zhao J. , Seehra Mohindar S.
Published: July 2002

About 20 powder samples of the fcc diluted system NipMg1−pO (0.06<p<1) were prepared and their structural and magnetic properties were measured. The lattice constant a(p) fits the variation a(p)=4.2115−0.0340 p. From the magnetic susceptibility versus temperature data, the Néel temperatures TN are determined. The variaton of t= TN(p)/TN(1) versus p is found to be similar to that in CopMg1−pO for p≳0.32 and it is found to fit the predicted values for a simple cubic Heisenberg antiferromagnet. A theoretical justification for this observation is advanced.
Deterministic and stochastic spin diffusion in classical Heisenberg magnets
Authors: Liu Jian-Min , Srivastava Niraj , Viswanath V. S. , Müller Gerhard
Published: July 2002

This computer simulation study provides further evidence that spin diffusion in the one-dimensional classical Heisenberg model at T=∞ is anomalous: 〈Sj(t)⋅Sj〉 ∼t−α1 withα1 ≳1/2. However, the exponential instability of the numerically integrated phase-space trajectories transforms the deterministic transport of spin fluctuations into a computationally generated stochastic process in which the global conservation laws are still satisfied to high precision. This may cause a crossover in 〈Sj(t)⋅Sj〉 from anomalous spin diffusion (α1 ≳ 1/2) to normal spin diffusion (α1 = 1/2) at some characteristic time lag that depends on the precision of the numerical integration.
Dependence of saturation magnetization and coercivity of Co-Cr/Al multilayered films on Co-Cr layer thickness
Authors: Takahashi T. , Ikeda N. , Naoe M.
Published: July 2002

Co81Cr19/Al multilayered films with thicknesses of Co81Cr19 layers in the range of 46–170 Å and Al ones of 7 Å have been prepared on glass-slide substrate at room temperature by using the facing targets sputtering (FTS) apparatus. The dependence of the magnetic and crystallographic characteristics on the thickness of Co-Cr layers have been investigated. The magnetoresistance effect of the specimen films have been also examined. The intrinsic Co81Cr19 layers were composed of hcp phase crystallites with well orientation of the c axis normal to the film plane. Both the crystallinity of Co81Cr19 layers was improved and the d spacing between the c planes was expanded by using the Al interlayers as ultrathin as 7 Å. The easy direction of magnetization in the films was perpendicular to the film plane. The saturation magnetization, the coercivity, the in-plane squareness ratio and the anisotropy field depended strongly on the thickness of Co81Cr19 layer. On the other hand, the magnetoresistivity ratio was negative and its absolute value was as small as 0.13%.
Ground-state properties for an easy-plane spin-one ferromagnet: The coupled-cluster method
Authors: Lo C. F. , Pan K. K. , Wang Y. L.
Published: July 2002

In this paper we have investigated the ground state of an easy-plane spin-one ferromagnet: H = D∑i(Sxi)2 −(J/2)∑(i, j)Si⋅Sj −h∑iSzi, using the coupled-cluster method. The mean-field approximation is commonly used in calculations of thermodynamic quantities for such systems because of the complexities caused by the single-ion anisotropy term. However, in the mean-field approximation both quantum and spin fluctuation correlations are neglected. Above the critical point, the zero-temperature series expansion method has been used to obtain estimates of the critical crystal field potential (Dc) and critical exponent of the susceptibility. Using the coupled-cluster method we obtained the ground-state energy, magnetization and critical point for both two- and three-dimensional lattices.
Ferromagnetic resonance studies of anisotropy in PtCo multilayers
Authors: Artman J. O. , DeSmet D. J. , Shao X. , Cates J. C. , Alexander C. , Parker M. R. , Lacey E. T. , Lord D. G. , Grundy P. J.
Published: July 2002

We report on K-band ferromagnetic resonance studies made on a sequence of PtCo multilayer films. Two principal results emerge: (a) the angular dependence of the resonance fields can be fitted only by a combination of second and fourth order anisotropy: E = Keff sin2 θ+ K4 sin4 θ, and (b) an additional resonance was observed at fields below the major resonance position in some of the specimens. Although these latter spectra were observed about the surface normal only over a restricted angular range, we were able to fit these lines as well with a combination of second- and fourth-order anisotropy. In each case the integrated absorption intensity of the secondary spectrum, when present, was comparable to that of the primary resonance. The physical origin of these additional spectra is not yet entirely clear.
Neutron diffraction study of ternary nitrides of the type R2Fe17Nx
Authors: Yang Ying-chang , Zhang Xiao-dong , Kong Lin-shu , Pan Qi , Yang Ji-lian , Ding Yong-fan , Zhang Bai-sheng , Ye Chun-tang , Jin Lan
Published: July 2002

We have carried out neutron diffraction measurements on powder samples of Nd2Fe17Nx and Y2Fe17Nx at room temperature. The refinements of the neutron data indicate that the nitrogen atoms occupy the 9e interstices in the nitride Nd2Fe17Nx (Th2Zn17 type, R3̄m) or the 6h interstices in the nitride Y2Fe17Nx (Th2Ni17 type, P63/mmc), respectively. At room temperature, both Nd2Fe17Nx and Y2Fe17Nx adopt a magnetic structure in which the easy magnetization direction is perpendicular to the c axis. Using the above results, we have briefly discussed the effect of a nitrogenation on the magnetocrystalline anisotropy of the Sm sublattice of Sm2Fe17Nx.
The effect of a magnetic underlayer on the magnetic properties of plated Permalloy (abstract)
Authors: Ryan P. J. , Mowry G. , Anderson S. , Amin N. , Yan Y.
Published: July 2002

The effects of a magnetic underlayer on the magnetic behavior of overlayer/underlayer combinations were investigated. Permalloy underlayers of 100 nm thickness and composition 82% Ni-18% Fe by weight were sputter deposited on 3-in.-diam Si substrates. Magnetic orientations of the underlayers were set at 0°, 45°, and 90° with respect to the orientation of a subsequently plated Permalloy (79%Ni-21%Fe overlayer. Several film combinations were generated on each of the various underlayer configurations with plated thicknesses ranging from 0.1 to 2.0 μm. Spatial maps of magnetic orientation and Hk for underlayers and underlayer/overlayer combinations were collected using a modified Kerr BH imager (Kerr BHI) designed from Gudeman.1 The maps covered a 5 cm×5 cm square region with 5 mm spacing between points. Comparison of the maps before and after plating shows a partial reduction in the measured Hk values for film systems with large underlayer/overlayer orientation differences. A uniform decline in the effect of the underlayer to the overall orientation direction as film thicknesses increase was also observed.
Absence of temperature-driven first-order phase transitions in systems with random bonds (invited)
Authors: Berker A. Nihat
Published: July 2002

Temperature-driven first-order phase transitions that involve symmetry breaking are converted to second order by the introduction of infinitesimal quenched bond randomness in spatial dimensions d≤2 or d≤4, respectively, for systems of n=1 or n≥ (R18)2 component microscopic degrees of freedom. Even strongly first-order transitions undergo this conversion to second order! Above these dimensions, this phenomenon still occurs, but requires a threshold amount of bond randomness. For example, under bond randomness, the phase transitions of q-state Potts models are second order for all q in d≤2. If no symmetry breaking is involved, temperature-driven first-order phase transitions are eliminated under the above conditions. Another consequence is that bond randomness drastically alters multicritical phase diagrams. Tricritical points and critical endpoints are entirely eliminated (d≤2) or depressed in temperature (d≳2). Similarly, bicritical phase diagrams are converted (d≤2) to reentrant-disorder-line or decoupled-tetracritical phase diagrams. These quenched-fluctuation-induced second-order transitions (a diametric opposite to the previously known annealed-fluctuation-induced first-order transitions) should lead to a multitude of new universality classes of criticality, including many experimentally accessible cases.
Production and magnetic properties of FeCx on exfoliated MoS2
Authors: Templeton T. L. , Gee M. A. , Joensen P. , Li X.-Z. , Rajora O. , Arrott A. S. , Curzon A. E. , Frindt R. F. , Schurer P. J. , LaCombe J. L.
Published: July 2002

Fe(Co)5 is thermally reduced to Fe(C) in the presence of monomolecular flakes of MoS2. The magnetic properties of particles produced by the decomposition of Fe(CO)5 and subsequent thermal annealing are described. Comparison of the properties of primarily χ-Fe5C2 carbides prepared with and without the presence of MoS2 flakes show that enhanced coercivity is achieved by including MoS2 in the processing.
Spin-polarized core-level photoemission of oxidized Fe(001)(invited)
Authors: Sinkovic B. , Johnson P. D. , Brookes N. B. , Clarke A. , Smith N. V.
Published: July 2002

The combination of spin-polarization detection with core-level photoemission to give spin-polarized electron spectroscopy for chemical analysis provides new information on the oxidation of an iron surface. During the initial stage of oxidation the predominant phase is of a ferrimagnetic γ-Fe2O3 form. The observed antiferromagnetic coupling of this oxide with the iron substrate is attributed to the superexchange interaction mediated by an oxygen ion. This provides evidence for a site exchange mechanism during the initial oxidation. Annealing transforms this oxide into an antiferromagnetic FexO form which is also present at the initial stage.