bluuebunny/crossref_metadata_2025 huggingface dataset:
Heating microscopic particles with laser beams
Authors: Bennett Herbert S. , Rosasco Gregory J.
Published: February 2003

A number of recently developed techniques for fine particle and aerosol measurement employ focused high-irradiance (power per unit area) laser beams. A knowledge of the temperature profiles in the media surrounding microsamples and the temperature of the microsample is essential for the design and operation of these instruments. In this paper, we develop theoretical models to estimate the final temperature and temperature profiles associated with microscopic particles heated by intense laser beams. We conclude that a heat-sinking medium, such as sapphire, can be effective in maintaining sample temperatures at acceptable levels for nondestructive analysis. This paper also examines the time required for particle temperatures to reach a steady-state time-independent value. These results are useful for assessing the effectiveness of laser power modulation techniques in these instruments. And finally, the above results are used to calculate the optical path-length changes near the heated microparticle due to temperature rises in the host medium.
Energy propagation properties of piezoelectric surface waves on cubic crystals
Authors: Shirasaki Hirokimi , Makimoto Toshio
Published: February 2003

The wave surface of piezoelectric surface waves propagating on the Z-cut metal-coated surface of a semi-infinite cubic crystal (class 4̄3m or 23) is calculated from the envelope of equiphase planes using the Lagrange multiplier method. It is found that the wave surface shows the cusps if the crystal is in the Cu region (c12≳c11−2c44) and has strong anisotropy.
Asymptotic expressions for piezoelectric surface waves excited by the buried mechanical and electrical point sources
Authors: Shirasaki Hirokimi , Makimoto Toshio
Published: February 2003

The asymptotic expressions for the piezoelectric surface waves excited by the buried mechanical and electrical point sources are obtained by using the stationary-phase method developed by Lighthill. It is found that the amplitudes of the piezoelectric surface waves propagating in the directions which correspond to the points of zero curvature on the slowness surface are subject to a comparatively small decay at the rate O(r−1/3) with distance, as opposed to a decay of O(r−1/2) for the ordinary surface waves.
The degeneracy factor of the gold acceptor level in silicon
Authors: Ralph H. I.
Published: February 2003

Several attempts have been made to derive the degeneracy factors of gold in silicon in the past, some of the estimates being quite large. It is pointed out in this paper on quite general grounds that the acceptor degeneracy factor must be close to unity. Assuming that the gold is on a substitutional site and that there are no accidental degeneracies, it is shown that it lies in the range 2/3 to 4. Furthermore, though no conclusive evidence exists, it is shown that there is reason to believe that the gold behaves as a transition metal in which case the acceptor degeneracy factor is 4.
Oscillatory magnetoresistance of p-type CdCr2Se4 single crystals
Authors: Kodama Kunihiko , Niimi Tatsuya
Published: February 2003

The dependence of the magnetoresistance on the magnetic field direction and temperature was measured on p-type Ag-doped CdCr2Se4 single crystals with electrical current flow in the 〈111〉 and the 〈001〉 directions. The negative magnetoresistance became maximal at 136 °K and was found to vary periodically with the rotation of the magnetic field direction.
Impact ionization phenomena initiated by the acoustoelectric effect in n-GaAs
Authors: Eizenberg M. , Fisher B.
Published: February 2003

Acoustic flux amplified from thermal background in semidegenerate n-GaAs at liquid-air temperature is accompanied by electric fields that initiate impact ionization. When the acoustic flux is concentrated in a narrow domain the interplay between the impact and the acoustoelectric effect brings about current oscillations of frequencies in the MHz range that increase monotonically with the net gain factor of the acoustic flux measured prior to the onset of impact. When wide stationary acoustic domains are generated in such samples, the impact causes an increase of the saturation current typical of the acoustoelectric effect. For initially applied fields higher than the threshold for impact, current modulation is observed when the acoustic flux is still in the embryonic stage and its incubation time is increased. The threshold field for impact in epitaxial layers is about 1500 V/cm, while in bulk samples it is much higher. At high power levels these instabilities may bring about the formation of current filaments that burn channels across the samples. The experimental results and a semiquantitative analysis of the instabilities are presented in detail in this work.
Impurity doping of chemical-vapor-deposited Nb3Ge and its effect on critical-current density
Authors: Braginski A. I. , Roland G. W. , Daniel Michael R. , Santhanam A. T. , Guardipee K. W.
Published: February 2003

In an earlier work, we demonstrated that high self-field and low-field critical-current densitites Jc of the order of 106 A cm−2 can be attributed to flux pinning on a dispersed Nb5Ge3 tetragonal phase present in Nb3Ge3 layers grown by chemical-vapor deposition (CVD). In this study, we examined the effect of impurity gas additions on Jc and the critical temperature Tc of the A15 superconducting phase. The gas impurities were N2, C2H6, and CO2. The impurity concentration in the gas phase was varied over three to four orders of magnitude to establish tradeoffs between Tc deterioration and Jc enhancement. The x-ray phase analysis of samples containing the highest impurity concentrations indicated by the presence of niobium nitrides and carbides, respectively. The Tc was affected least by N2 and most by CO2 additions. Doping by N2 or C2H6 resulted in A15 deposits free of the tetragonal phase and having Jc’s of the order of 106 A cm−2, comparable to the best Nb5Ge3-containing samples. The grain size of deposits was estimated from thinned specimens using transmission electron microscopy. Correlation of Jc with the microstructure of the sample suggested that predominant flux pinning occurs on impurities incorporated in Nb-Ge layers and on the accompanying defects.
Summation curves for flux pinning in superconductors
Authors: Kramer Edward J.
Published: February 2003

Flux pinning in irradiated superconductors having either dislocation-loop or void microstrutures is reexamined. The elementary interaction force fp can be accurately computed for such defects if their size is known from transmission electron microscopy. Data exist for a range of defects for which fp varies by over a factor of 104. If the data for voids and dislocation loops are plotted as Q, the volume pinning force per defect, versus fp at a given reduced induction b, the sets of data for each defect species overlap to form a single summation curve. This curve is not correctly described by either of the two most widely used summation models, the direct summation or the statistical summation of Labusch. The empirical summation curve runs parallel to, but a factor ?4 below, the direct summation curve at high fp but bends to decrease approximately as f2p at low fp. Increasing b produces a shift in the summation curve, parallel to the direct summation Q=fp line, by a factor which is proportional to (1−b)2. This shift is the origin of the peak effect which appears at high b for low fp defect microstructures. The failure of the statistical theory is thought to result from the presence of flux-line dislocations in the flux-line lattice which produce both a large decrease and a dispersion in the local threshold force necessary for pinning centers to be effective.
Qualitative theory of the nonlinear behavior of coupled Josephson junctions
Authors: Imry Y. , Schulman L. S.
Published: February 2003

We use qualitative mathematical methods for the analysis of the time dependence of the phase differences and, hence, the dynamic I-V characteristics for two coupled Josephson point junctions. All our qualitative results are supported by numerical calculations. The case of a single point junction is reviewed and extended; it is proved that periodic trajectories in the phase plane are attractors and that they are therefore unique for a given junction and dc driving current I. Center of mass and relative coordinates are introduced for two inductively coupled junctions and the latter coordinate is shown to remain bounded. All static solutions are obtained and their stabilities analyzed. We find that the end of stability of a given solution is never a Hopf bifurcation and, hence, is marked by a finite jump to a dynamic or another static solution. The dynamic solutions are analyzed using perturbation theory for strongly coupled junctions. An approximation for the beating mode in weakly coupled junctions is presented and approximate expressions for the beat period derived. Interesting symmetries of the solution are found for a set of special values, a set which becomes dense for weak interjunction coupling.
The dynamical behavior of magnetic domain walls and magnetic bubbles in single-, double-, and triple-layer garnet films
Authors: de Leeuw F. H. , van den Doel R. , Robertson J. M.
Published: February 2003

The dynamical behavior of straight magnetic domain walls and propagating magnetic bubbles in single-, double-, and triple-layer lanthanum gallium garnet films is reported. In the study of straight walls in the single-layer films, a good agreement is obtained between the observed and the calculated values of the domain-wall width parameter Δ, the derivative of the peak velocity to in-plane field at high in-plane fields, and the derivative of the saturation velocity to in-plane field at a moderate drive field and high in-plane fields H1. The saturation velocity (at H1=0) decreases with decreasing film thickness, which is in disagreement with theoretical predictions. A propagating bubble in a single-layer film exhibits an overshoot. In double- and triple-layer films, the observed and calculated Δ values disagree in most cases, and the straight wall and propagating bubble saturation velocities are significantly higher than in single-layer films. Overshoots and low-frequency oscillations are observed in the saturation regime of straight walls. The resulting high wall masses are attributed to stacking of horizontal Bloch lines on the film surface(s). From the measurements in in-plane fields, we conclude that the saturation velocity and the peak velocity in a double- and a triple-layer film depend on the polarity of the in-plane field, which is always perpendicular to the straight wall. It is found that the saturation region in double- and triple-layer films can be subdivided in three parts. This is explained qualitatively, and a calculation is made of the saturation velocity in double- and triple-layer films. This calculation shows good agreement with experimental results.
Thermal depolarization current study of polypyromellitimide
Authors: Tanaka T. , Hirabayashi S. , Shibayama K.
Published: February 2003

Thermal depolarization current (TDC) of polypyromellitimide film was measured in order to obtain knowledge of the charging and discharging mechanisms of carriers in polypyromellitimide. Two peaks are observed at 173 (α) and 50 °C (β) in the dried film. The β peak attributed to dipole orientation polarization is probably associated with residual reactive groups in polypyromellitimide. The α peak shows nonlinear dependence on polarization electric field Ep. The sign of the current changes with small collecting electric field Ec which is applied during the TDC measurement. The α peak depends on electrode materials. The α peak is considered to be attributed to space-charge polarization due to trapping of electrons injected from the cathode in the vicinity of the polymer film surface. The nonlinear Ep dependence of the α peak can be described by a two-site hopping model.
Photoluminescence in nitrogen-doped gallium arsenide phosphide (GaAs1−xPx : N) for 0.6<x<1
Authors: Roessler David M. , Swets Don E.
Published: February 2003

In GaAs1−xPx : N, the composition parameter x strongly affects both the spectral position of the photoluminescence and its absolute intensity. There has previously been some controversy in the literature regarding the identification of the observed emission. The present work describes the changes in wavelength, intensity, and relative strength of spectral features at 77 and 296 K as a function of alloy composition in the range 0.6<x<1. The edge emission at 77 K can be identified in terms of contributions from isolated nitrogen atoms and from pairs of nitrogen atoms, together with optical-phonon replicas of the exciton transitions.
A new method for measuring the optical activity of crystals and the optical activity of KH2PO4
Authors: Kobayashi J. , Takahashi T. , Hosokawa T. , Uesu Y.
Published: February 2003

A new and general method has been developed by which the optical activity of crystals can be measured along different directions from the optic axes. The principle of the method is to measure accurately the intensity of emergent light from parallel and crossed polarizers between which the specimen is properly oriented. The experimental apparatus is relatively simple and needs no elaborate machinery. By this method, gyration and birefringence can be obtained simultaneously as a function of wavelength. As a test of the applicability of the method, a component of the gyration tensor g11 and birefringence ne−n0 of quartz have been observed as a function of wavelength, e.g., g11=5.69×10−5, and ne−n0=9.15×10−3 at a wavelength of 550 nm. This method was also applied to the study of the optical activity of KH2PO4. It was found that the nonenantiomorphous D2d phase (paraelectric) of KH2PO4 is optically active, g11=2.28×10−4 at a wavelength of 506 nm.
Nonlinear pulse propagation in high-energy glass laser amplifiers
Authors: Kato Daisuke
Published: February 2003

Characteristics of high-energy/power amplifiers including large-signal gain, extraction efficiency, and pulse deformation are analyzed in terms of material and operating parameters. A figure of merit for large-signal amplifier material is defined, which is inversely proportional to the stimulated-emission cross section. A method for detailed pulse tailoring in nonlinear amplifiers is developed. It is found that a high stored-energy density, which is obtainable with a small stimulated-emission cross section, is very important for achieving high gain and tolerable pulse deformation. The high stored-energy density is also found to be effective for suppressing laser beam degradation due to nonlinear refractive-index effects.
Relativistic solution to the problem of scattering by a rotating dielectric column
Authors: Goto H. , Shiozawa T.
Published: February 2003

The problem of the scattering of an obliquely incident plane electromagnetic wave by a rotating dielectric column is discussed on the basis of Maxwell’s equations and the constitutive relations of the Minkowski type for rotating media. Consider a homogeneous isotropic nondispersive dielectric column rotating at constant angular velocity around its axis, with its peripheral velocity assumed to take an arbitrary value smaller than the vacuum velocity of light. Then, the scattering properties of the rotating dielectric column are investigated in detail with the aid of numerical examples. From the numerical examples for the scattering pattern and the backscattering cross section, it is found that the scattering of electromagnetic waves by a dielectric column is modified in an interesting manner by its rotational motion.
First- and second-order Bragg interactions in an active medium
Authors: Seshadri S. R.
Published: February 2003

The first- and the second-order Bragg interactions in an unbounded active medium having a sinusoidally varying permittivity or gain in the direction of progression of the interacting waves are investigated. In the first-order Bragg interaction, there is absolute instability of the participating waves. In the second-order Bragg interaction, the waves are convectively unstable with their spatial amplification reduced in the Bragg region by the destructive interference of the two interacting waves. The nature of these instabilities are analyzed and physical explanations for the various characteristics are provided. When the gain of the medium is an order magnitude smaller than the modulation index, the absolute instability, instead of taking place in the first, occurs, in the second Bragg region. The importance of incorporating the gain in a manner that is consistent with the material dispersion law is emphasized.
Spectroscopic technique for the measurement of residual stress in sintered Al2O3
Authors: Grabner Ludwig
Published: February 2003

Using the R-line fluorescence of trace Cr3+ in sintered Al2O3 as an example, a method of analysis is outlined for determining the residual microstress and macrostress in a polycrystalline aggregate. It uses the shift and broadening, induced by residual stress, of a line due to a transition in an atomic system dissolved in the aggregate. For sintered Al2O3 from three different manufacturers, but made for the same purpose, the isotropic and shearing components of the residual microstress and macrostress are listed in tabular form. For the isotropic component of the microstress a distribution is found, with a mean value of ∼2 kbar, in which tension and compression are equally probable.
Intense microwave generation by the negative-mass instability
Authors: Uhm Hwan-sup , Davidson Ronald C.
Published: February 2003

This paper examines the negative-mass stability properties of an E layer for transverse electric (TE) and transverse magnetic (TM) waveguide modes in a conducting cylinder. The analysis is carried out for a relativistic non-neutral E layer aligned parallel to a uniform axial magnetic field B0êz, within the context of the assumptions that the electron motion is ultrarelativistic (γ0≫1) and that (ν/γ0)1/3≪1, where ν is Budker’s parameter and γ0mc2 is the electron energy. One of the most important features of the analysis is that the axial energy spread can have a large influence on the stability behavior for both the TE and TM waveguide modes. By an appropriate choice of system parameters, it is shown that the spectrum of microwave radiation generated by the negative-mass instability can be very narrowband.
Reactive diffusion and electronic structure at the nickel/selenium interface
Authors: Nielsen Paul , Ritsko John J.
Published: February 2003

Ultraviolet photoemission spectroscopy has been used to study reactive diffusion at the interface between clean nickel and evaporated selenium films in ultrahigh vacuum. Photoelectron-energy-distribution curves were measured at 10.2 eV for sputter-cleaned nickel, evaporated selenium and nickel, and the reaction product nickel selenide, which is metallic. By depositing thick selenium films and monitoring the photocurrent as a function of time and temperature, the growth of nickel selenide in the interface region was measured. In agreement with the theory of reactive diffusion, the nickel selenide layer increased in thickness as the square root of the product of the growth constant k and time, where k=1×108 exp(−1.35eV/kBT) cm2 sec−1. This rate is independent of impurity concentrations in both the nickel and selenium up to several atomic percent. A thin (∼7 Å) nickel oxide layer prevented nickel selenide formation. The electronic structures of selenides prepared with various compositions were determined, and it was found that the interfacial selenide is the Ni1−xSe phase with x less than 0.23.
Laser-fusion experiments utilizing a 4π illumination system
Authors: Storm E. K. , Swain J. E. , Ahlstrom H. G. , Boyle M. J. , Rupert V. C. , Phillion D. W.
Published: February 2003

A focusing system which utilizes two f/0.47 doublets in conjunction with ellipsoidal mirrors produces two focusing cones with half-angles of 81.5°. This system has been used with the Lawrence Livermore Laboratory Janus 1.06-μm laser to irradiate and implode DT-filled glass microshells of ∼70 μm diameter. The purpose of the system was to provide more uniform heating of the pusher and more uniform compression of the DT fuel than had been obtained when irradiating targets using f/1 lenses. Neutron yields of ∼107 per event have been obtained at power levels of ∼0.4 TW. X-ray micrographs show that improved uniformity of heating and implosion sphericity are achieved. Data are also presented which add further confirmation of the importance of absorption by plasma wave resonance for non-normal incidence of the laser light on the target surface.
Depth profiles of 3He ions implanted into solids at energies between 20 and 60 keV
Authors: Bo/ttiger J. , Jensen P. S. , Littmark U.
Published: February 2003

Depth profiles of 20–60-keV 3He ions incident on surfaces of C, Al, Si, V, Ni, and Zr have been measured using the 3He(d,α)1H reaction. A comparison of the results with theoretical predictions shows rather large discrepancies.
Characteristics and optimization of the two-photon-excited 16-μm laser in 14NH3
Authors: Pummer H. , Bischel W. K. , Rhodes C. K.
Published: February 2003

Stimulated emission at 15.88 and 15.95 μm has been obtained in 14NH3 utilizing two-photon excitation. Total output energies on the order of 1 mJ have been observed in configurations which can be readily scaled to higher values. A discussion of the parameters available to control the operation of this system is given along with experimental data on laser output energy, divergence, the role of the optical Stark effect, pressure dependence, and spectral control with absorbing gases. These mechanisms can be generally applied for efficient down-conversion throughout the infrared.
Scattering of an electromagnetic wave from a very rough semi-infinite dielectric plane (exact treatment of the boundary conditions)
Authors: Sung C. C. , Eberhardt W. D.
Published: February 2003

The reflected and refractive fields are calculated for a very rough surface which is assumed to be a set of tangent planes with small corrections due to the local finite radii of curvature. A perturbation technique similar to those used in the moderately rough surface calculations is developed to treat the solution for the tangent planes as the unperturbed solution with the curvature correction as the perturbation. Our results are expressed in terms of the slope distribution function of the tangent planes and the average radius of curvature. Numerical results for scattering of both polarizations are obtained. The depolarization calculation is shown to be consistent with the experimental data. Further, the relationship between the surface model and the conventional Gaussian model is discussed, and a comparison with previous works is given.
Electric field dependence of a uniaxial anisotropy energy in lithium ferrite
Authors: Rado G. T. , Ferrari J. M. , Remeika J. P.
Published: February 2003

By adapting a thermodynamic theory and method of measurement previously introduced for magnetite by two of the present authors, it is shown that at 77 °K the anisotropy energy of ionically ordered Li0.5Fe2.5O4 contains a component which is electric-field-dependent as well as shape-independent, and that it has uniaxial symmetry rather than the expected cubic symmetry. The magnetic field dependence of the magnetically induced electric polarization in zero electric field is predicted, and it is shown that in all but small magnetic fields this measured polarization is in good agreement with the proposed theory. Experimental evidence for the existence of a ’’skin’’ layer in Li0.5Fe2.5O4 crystals is also presented.
A theory relating NMR satellite data to the electronic structure of iron group atoms in copper
Authors: Cohen J. David , Slichter Charles P.
Published: February 2003

A simple one electron model is used to calculate the spin density oscillations near Cr, Mn, and Fe impurities in copper recently determined from NMR satellite spectra. We obtain the positions and widths of Anderson-like scattering ’’resonances’’ and find that the configurations of the three impurities are 3d4, 3d5, and 3d7, respectively, in agreement with recent findings of Abbas by an independent method. Based on a 3 parameter screened potential with exchange, the model gives good agreement with the near neighbor isotropic Knight shifts, is consistent with bulk susceptibility and high temperature resistivity, and in most cases agrees with the axial component of the measured anisotropic Knight shifts. The model is easily extended to account for trends observed as one moves across the entire iron group.
Size effects in critical phenomena in iron whiskers
Authors: Heinrich B. , Arrott A. S. , Noakes J. E.
Published: February 2003

The Curie temperatures of whiskers of various sizes are compared by measuring the temperature dependence of the magnetic fields at which each whisker shows saturation in its midsection with two or three samples in the same detector coil. Whiskers of thicknesses of 50 μm or less show a decrease in Curie temperatures compared to thicker whiskers. The a.c. response near Tc of the thinner samples have exhibited long time dependent effects which might be associated with impurities and strain.
Multicomponent CPA theory for spin-wave excitations in diluted ferromagnets
Authors: Roth L. M.
Published: February 2003

We describe a multicomponent coherent potential approximation for the diluted ferromagnet, which includes the effect of the environment on the Ising diagonal energy levels of a site as does previous work, and which also takes account of short-range order, i.e., the correlation between environments of neighboring sites. Results are presented for simple and body centered cubic cases, and compare well with computer simulation results. They show little difference from the single site CPA theory, a simplified version of which is presented. We expect to find greater differences for the diluted antiferromagnet.
Excitations of isolated clusters of magnetic ions
Authors: Svensson E. C. , Harvey M. , Buyers W. J. L. , Holden T. M.
Published: February 2003

The neutron scattering by isolated clusters of Mn2+ ions in a single-crystal specimen of KMn0.18Zn0.82F3 has been studied as a function of wave-vector transfer Q at 4.3 K and as a function of temperature T at Q=2πa−1(0.55,0.55,0.55). At low T we observe peaks corresponding to the ground-state transitions of isolated pairs and triplets and to two excited-state transitions of pairs. The frequencies υ of these peaks lead directly to accurate values for the exchange interaction J, e.g., 0.100±0.004 THz and 0.098±0.002 THz from the ground-state transitions of pairs (υ=2J) and triplets (υ=7J) respectively. Exact calculations of the neutron scattering by isolated pairs, triplets and quartets of Mn2+ ions interacting via nearest-neighbor antiferromagnetic exchange give a reasonably good description of the principal features of the measurements. There are, however, discrepancies that are probably attributable to the scattering by larger clusters.
Resistivity and magnetoresistance study of various s,p impurities in ferromagnetic hosts
Authors: Ross R. N. , Williams Gwyn , Price D. C.
Published: February 2003

We have measured the electrical resistivity between 4.2 K and 300 K and longitudinal and transverse magnetoresistance at 4.2 K of several Ni, Co and Fe based alloys containing various s,p impurities such as Sn and Sb. The deviations from Matthiessen’s Rule (DMR) derived from the resistivity data have been fitted to the two current models of Campbell et al. and values for α (the ratio of spin up to spin down resistivities at the impurity site), μ (the same ratio at host sites) and D (the coefficient of spin mixing scattering events) estimated. These data yield values of α close to one, as expected from a simple non-magnetic s,p screening state around such impurities. The magnetoresistance data also yield values of α close to 1, but there are consistent differences between these data and the two current model predictions with α=1, especially for the Ni and Co based systems.
Coulomb and exchange scattering amplitudes from spin dependent residual resistivities in Fe and Ni hosts
Authors: Stearns Mary Beth
Published: February 2003

The spin dependent residual resistivities for a large number of solute atoms in Fe and Ni based ternary alloys are analyzed as arising from three main sources. 1. Coulomb scattering from the impurity charge (or volume) perturbation. This amplitude is found to be similar to that for Cu based alloys. 2. Scattering from a localized moment perturbation at the solute atom. Both a potential and exchange amplitude are found to be spin-dependent and about the same per μB for Fe and Ni hosts. 3. A more widespread moment perturbation in the host surrounding the solute atom. The shape of this perturbation depends upon whether direct Coulomb exchange or hybridization effects dominate. In Ni, usually hybridization effects dominate and give predominately negative host perturbations. In Fe, Coulomb exchange dominates and the shape of the host perturbation depends upon the number of itinerant d-like electrons connected with the solute atom.
Anisotropy from quadrupole scattering in magnetically ordered rare-earth compounds
Authors: Sablik M. , Levy P. M.
Published: February 2003

Anisotropy from the quadrupole scattering contribution to the electrical resistivity of magnetically ordered rare-earth compounds is examined. Considering the conduction electrons in plane-wave states, we find that the principal contributions to the anisotropic scattering come from the p and d partial wave scattering. We take into account the crystal field splitting of the rare-earth ions’ 4fn electrons and therefore include the effects of inelastic scattering. We consider the case of zero magnetic field so that anisotropy only appears below the ordering temperature of the system. The theory is applied to dysprosium and holmium antimonide.
Magnetothermopower and magnetoresistivity of PtCo
Authors: Lee C. W. , Foiles C. L. , Bass J. , Cleveland J. R.
Published: February 2003

We review the behavior of the thermopower, magnetothermopower, and magnetoresistivity of dilute PtCo alloys, and present new results which extend the thermopower data to lower Co concentrations, the magnetothermopower to higher temperatures, and the magnetoresistivity data to higher Co concentrations. We report the first observation of a negative magnetoresistivity in PtCo.
Magnetoresistance effect of Ni-Co alloy films
Authors: Makino Y. , Okamoto T.
Published: February 2003

Ni-Co alloy is worth notice as a material for fabricating a magnetoresistance element, because of the highest magnetoresistance anisotropy (Δρ/ρ0) in the ferromagnetic alloys. We studied the magnetoresistance anisotropy and the crystal structure on the films of the Ni-Co alloy system (40 Ni–60Co∼81Ni–19Co). In this study we found the following facts: (1) A new ordered phase exists in the films around at the composition 50Ni–50Co prepared at a substrate temperature above about 550 °K. (2) This ordered phase is accompanied with a newly proposed superstructure. (3) A close relation exists between the magnetoresistance anisotropy and the degree of order, and the films in the ordered state have a higher anisotropy ratio (Δρ/ρ0) than the bulk value. This fact is important in the practical application, such as a magnetic field sensor.
Spin-dependent phonon Raman scattering and electronic structure of CdCr2X4 (X:S,Se)
Authors: Koshizuka N. , Yokoyama Y. , Okuda T. , Tsushima T.
Published: February 2003

Spin-dependent (SD) phonon Raman scattering in ferromagnetic CdCr2X4 is closely associated with the resonance effect. In order to clarify the correlation between the excitation energy dependence of the SD phenomenon and the electronic structure, detailed temperature dependences of absorption and Faraday rotation spectra were measured between 20 and 300 K for ’’red-shifting (RS)’’ transitions in CdCr2S4 ∼1.9 eV) and CdCr2Se4 (∼1.2 eV). We found that the RS absorption peaks consists of a pair of electronic transitions with the energy separation of about 0.07 eV at 20 K. It turned out that the SD scattering cross section for Raman active phonon modes T2g and A1g in CdCr2S4 observed with red excitation light are caused by the resonance with the pair transitions. Magnetic circular polarization properties of Raman spectra for CdCr2S4 were measured in the applied fields up to 45 kOe in the Faraday configuration. The polarization and field-induced effects observed with Kr 647.1 nm excitation light support the idea of SD resonance scattering. SD effects for phonon modes T2g and A1g are also found with higher excitation energies C1 (2.4 eV; CdCr2S4, 2.0 eV;CdCr2Se4) and C2 (2.3 eV;CdCr2Se4), respectively. The correlations between the SD phonon scattering and the electronic structures are discussed on the basis of proposed transition diagrams.
Coherent generation of magnons by optical techniques
Authors: de Araujo Cid B. , Rezende S. M.
Published: February 2003

A new technique for the coherent excitation of magnons is proposed which is based on the magnetic Raman nonlinearity. The excitation is obtained by mixing two laser beams with different frequencies (ω1,ω2) under phase-match conditions [when (ω1−ω2) is equal to the frequency of one magnon mode and (k1−k2) is equal to the magnon wavevector]. The method allows selective excitation in frequency and wavevector and may by useful for magnon relaxation measurements. The proposed process is analyzed by quantum statistical methods. The number of excited magnons and the coherence properties of the generated states are investigated by using the representation of coherent magnon states. The results show that it is possible to excite a magnon population of the same order of magnitude as in nonlinear magnetic resonance experiments by using lasers with powers of hundreds of watts. The possibility of experimental observation is analyzed in detail for both ferromagnetic and antiferromagnetic materials.
Electronic Raman scattering from magnetically ordered Ni compounds
Authors: Abdalian A.T. , Moch P.
Published: February 2003

Raman scattering from high energy excitons has been measured in KNiF3, K2NiF4, NaNiF3 and NiF2 with the help of ultraviolet laser excitation. At T=2 K, the spectra consist of sharp excitonic lines, accompanied by a broad vibronic band showing pronounced structure. Attention is focused on Raman transitions from the 3A2g ground state to the 3T2g (∼6500 cm−1) and the 3Ta1g (∼11 000 cm−1) excited states. The observed polarized spectra and their dependence upon an applied magnetic field are compared with previous absorption measurements on the same crystals and are discussed in terms of magnetic excitons.
Rotation and deformation of the optical indicatrix of hematite during the magnetic field-induced phase transition
Authors: Leycuras C. , Rudachevskii E. G. , Le Gall H. , Merkoulov V. S.
Published: February 2003

It is shown from experiment that a rotaion ρ and a deformation χ of the optical indicatrix appear during the transverse field-induced phase transition in hematite. Strong dependence of ρ and χ on the temperature, magnetic field Ha and the angle Ψ corresponding to the direction of Ha with respect to the C2 axis in the basal plane are observed. During the Morin transition, the evolution of the linear magnetic birefringence is very sensitive to the magnetic phase transition and this evolution is discussed from the dependences of the analytical expressions of ρ and χ on the rotation of the antiferromagnetic vector L.
Effect of the spin-flop transition on the Ni2+ fluorescence in MnF2
Authors: Panepucci H. , Soares E. , Yamazaki H. , King A. R.
Published: February 2003

The field dependence of the low temperature infrared fluorescence of Ni2+ in MnF2 up to 110 kG is reported and the changes occurring at the spin-flop transition at 94 kG are analyzed. These are accounted for by an upward shift of the fluorescent state energy of 16.7 cm−1 and a modification of the ground term splittings. Both effects are shown to arise from the flip of the sublattice magnetizations from the [001] to the [100] directions. From the measured shift of the excited state the exchange energy for the 3T2 term is estimated to be about 110 cm−1.
Investigation of the optical absorption of Fe3BO6 after oxygen annealing and under the influence of strong magnetic fields
Authors: Andlauer B. , Diehl R. , Skolnick M. S.
Published: February 2003

The absorption spectrum of oxygen-annealed Fe3BO6 in the range 4000–18000 cm−1 is examined in terms of polaronic absorption and crystal field transitions. Some absorption lines at the onset of the 4T1 band have been investigated in a magnetic field making possible their unambiguous identification and an assignment to the two distinct iron sites of Fe3BO6. The measurements yield insight into details of the spin structure and the field-dependent spin reorientation occurring in Fe3BO6.
Magneto-optical measurements on the layer type magnet ND3- (CH2)2-ND3CuCl4
Authors: Arend H. , v. Känel H. , Wachter P.
Published: February 2003

The linear birefringence (LB) of the layered antiferromagnet (CH2)2(ND3)2CuCl4 was measured in several crystallographic directions as a function of temperature, wavelength and magnetic field. The index ellipsoid rotates upon cooling around the monoclinic z axis. The temperature derivative of the LB, corresponding to the specific heat, when measured perpendicularly to the layers, shows a pronounced anomaly at TN=34.24±0.05 K. The nearly ideal 2-dimensional behavior encountered in the related compound (C2H5NH3)2CuCl4 is completely lost by the covalent inter layer coupling. The LB shows only a weak dependence on an applied magnetic field; however, the spin flop transition can be seen unambiguously at HSF=9.3±0.5 kOe (T=2 K). No Faraday effect could be observed as yet.
Magnetooptical Kerr spectra of substituted YIG
Authors: Višňovský S. , Krishnan R. , Prosser V.
Published: February 2003

An analysis of polar Kerr rotation (PKR) spectra of diamagnetically substituted Y3Fe5O12 (YIG) is proposed using the relation 2φK=aA (ω)+bB (ω) where φK is the PKR in min, a and b are the coefficients proportional to the magnetic moments of the octahedral and tetrahedral sublattices, A (ω) and B (ω) coefficients calculated from the PKR spectra of both YIG and lithium ferrite using the above relation. In this manner the spectral dependences of PKR both for the tetrahedral and octahedral diamagnetic substitution are calculated and the results compared with the experiment.
Giant intrinsic magnetic hardness due to randomized crystal field interactions in SmNi5−xCux
Authors: Oesterreicher H. , Parker F. T. , Misroch M.
Published: February 2003

Giant intrinsic magnetic hardness is found at low temperatures in structurally homogeneous materials SmNi5−xCux. Magnetic hardness peaks at a composition SmNi2.5Cu2.5 where the crystal field disorder due to compositional randomization is at a maximum. By comparison with SmCo5−xNix, where giant intrinsic magnetic hardness originates, in part, from fluctuations from site to site of the magnitude of moment and strength of exchange of the transition metal, magnetic hardness in the SmNi5−xCux is predominantly due to anisotropy and concomitant exchange fluctuations on Sm sites.
High field measurements of giant intrinsic magnetic hardness in SmCo5−xNix and SmCo5−yCuy
Authors: Foner S. , McNiff E. J. , Oesterreicher H. , Parker F. T. , Misroch M.
Published: February 2003

The phenomenon of giant intrinsic magnetic hardness in SmCo5−xNix and SmCo5−yCuy is investigated in applied fields up to 23.5 T. At 4.2 K, the average propagation field (approximate coercive field) Hp is ≃13.0 T, 22.0 T and 18.2 T for x=3, 3.6 and 4.2 respectively, and Hp is ≃12.0 and ≃23.0 T for y=2.5 and 3.6 respectively. At 77 K, values of Hp≃5.0 and ≃5.5 T for y=2.5. Some values of Hp at 4.2 K are the largest observed to date for any material. The results are consistent with models for thermally activated domain wall motion. For several materials the irreversible portion of the magnetization is not saturated at 23 T and 4.2 K. In these cases the maximum magnetization is less than that observed at 77 K.
Mixed valent SmB6 and gold-SmS: Metals or insulators?
Authors: Allen J. W. , Martin Richard M. , Batlogg B. , Wachter P.
Published: February 2003

We review the dc transport properties of mixed valent compounds SmB6 and gold-SmS and find the character of the ground state, metallic or insulating, to be an open question. The room temperature optical properties of SmB6 and gold-SmS display ordinary metallic behavior at high energy, but are very nonmetallic at low energy in that ℰ1 becomes positive like an insulator from about 0.1 eV down to the lowest energy measured. We show that these room temperature optical properties are consistent with a ’’bad-metal’’ model having either a sharp 4f resonance at the Fermi level, or a collective low frequency density fluctuation, and extract from the data a value ∼.08 eV for the 4f-5d mixing matrix element. But we point out that the possibility of an insulating ground state remains.
Coherent potential approximation treatment of intermediate valence in rare-earth compounds induced by alloying
Authors: Schweitzer J. W.
Published: February 2003

The coherent potential approximation (CPA) is applied to the description of intermediate valence induced by alloying as observed in the solid solutions Sm1−xRxS where R denotes a rare-earth element which is trivalent in the monosulfide. The description is based on the Falicov-Kimball model for metal-insulator transitions generalized to take into account the disorder associated with the R substitution. This disorder is treated within the CPA while the intra-atomic correlation on the Sm sites is also treated by the CPA in analogy with an alloy of divalent and trivalent Sm ions. The transition to an intermediate valence for Sm as a function of alloy composition is discussed in terms of the results of this treatment.
Field induced magnetic form factor of γ-Ce
Authors: Stassis C. , Loong C.-K. , Kline G. R. , McMasters O. D. , Gschneidner K. A.
Published: February 2003

In the present experiment polarized neutron scattering techniques have been used to assess the spatial distribution and temperature dependence of the magnetization induced in a single crystal of γ-Ce by a magnetic field of 60 kG. The measured form factor is found to be in agreement with the free ion 4f magnetic form factor of Ce3+. Comparison of the localized susceptibility, obtained in the present experiment, with bulk susceptibility measurements indicate that there is a rather large positive conduction electron contribution to the static susceptibility of γ-Ce. The localized moment is found to follow, between 300 and 115 K, a Curie-Weiss law with a paramagnetic Curie temperature of (−44±2.5) K. The measurements indicate that at approximately 100 K some ions of the γ-Ce crystal undergo a change in their electronic configuration.
Magnetic ordering in Ce-La and Nd-La alloys
Authors: Petersen T. S. , Legvold S. , Gschneidner K. A. , Tsang T.-W. E. , Moorman J. O.
Published: February 2003

Heat capacity, magnetic susceptibility, and electrical resistivity measurements have been made on a wide ranging set of Ce-La and Nd-La alloys. In the case of Ce it is found that less than 5 at. % of La will prevent the β (dhcp) to α (collapsed fcc) transition at T≲50 K. In the case of Nd-La only the dhcp allotrope is formed. Two magnetic ordering temperatures have been found for many of the samples. These are believed to be caused by antiferromagnetic ordering on the two different atomic sites in the dhcp structure, cubic and hexagonal. In both sets of alloys the two ordering temperatures coalesce into one for La concentrations ≳30%. Additional magnetic features in Ce-La alloys are explained by the formation of the fcc phase.
Low temperature magnetization and magnetostriction of single crystal TmFe2
Authors: Abbundi R. , Clark A. E.
Published: February 2003

The magnetization and magnetostriction of single crystal TmFe2 were measured as a function of temperature from 4 K to 300 K. TmFe2, because of its highly anisotropic 4f charge distribution, displays a huge magnetocrystalline anisotropy (K1) and magnetostriction (λ111) at cryogenic temperatures in spite of the high cubic symmetry of the C15 lattice and the tetrahedral symmetry of the Tm3+ site. The anisotropy spans the range from −5.3×105 erg/cm3 at room temperature to the extrapolated value of −5×108 erg/cm3 at 0 K. The saturated magnetic moment was found to be 74 emu/g, which is substantially larger than previous polycrystalline results. Magnetostriction measurements are consistent with ‖λ111‖≫‖λ100‖, and yield a saturation value of λ111(0) =−3520×10−6, which is appreciably larger than that previously reported. The rapid fall of the Tm3+ sublattice moment with temperature results in a rather low value of λ111=−210×10−6 at 300 K. The temperature dependence of λ111 closely follows single-ion magnetoelastic theory.
Magnetoelastic waves in rare-earth intermetallics
Authors: Hathaway K. B. , Cullen J. R.
Published: February 2003

A theory of low frequency magnetoelastic waves is developed for rare-earth intermetallic compounds crystallizing in the Laves-phase (C15) structure. The long-wavelength modes of the lattice are calculated in terms of three sets of force constants. The triply-degenerate set of oscillations in which only the rare earths move is shown to be the only set which can couple to the magnetization and external strain. A model Hamiltonian is developed which incorporates the energy of this mode and its interaction with acoustic vibrations and magnetization fluctuations.
Magnetoelastic interactions in holmium
Authors: Arellano M. E. , Pinatti D. G. , Donoho P. L.
Published: February 2003

We report here the experimental results of the change of the elastic constants c22, c33 and c66 as a function of the state of magnetization of single crystal holmium for the temperatures between 130 K and 300 K. We applied magnetic fields up to 75 kOe along the crystallographic a, b and c-axes. To analyze the experimental data we used a thermodynamic treatment of the change of the elastic constants as a function of the state of magnetization similar to Freyne’s. Using a non-linear least squares fitting procedure to the experimental results we obtained a set of magnetoelastic coupling coefficients.
Magnetostriction and magnetostrictivite effects in magnetic materials
Authors: Kléman M. , Labrune M. , Miltat J. , Nourtier C. , Taupin D.
Published: February 2003

Most magnetic materials undergo a spontaneous deformation due to magnetostriction. In any non-uniformly magnetized sample, this effect gives rise to internal stresses and lattice rotations. They were studied within the framework of infinitesimal dislocation theory. A magnetic wall may thus be represented by densities of infinitesimal quasi-dislocations located on the wall and a wall junction by a quasi-disclination (rotation dislocation) located along the junction. In the case of simple magnetic configurations, semiquantitative arguments suffice to compare experimental results obtained by means of X-ray topography with theoretical expectations. The agreement is good on the whole. For more complex configurations, X-ray topograph image simulation is required and partial results obtained in the case of a Dijkstra and Martius structure are presented.