bluuebunny/crossref_metadata_2025 huggingface dataset:
Reflection, absorption, and transmission of ultra-low-frequency electromagnetic waves through a Gaussian conductor
Authors: Hammond Richard T. , Davis Jon , Bobb Lloyd
Published: July 2002

The reflection, transmission, and absorption coefficients are derived for long-wavelength electromagnetic radiation propagating through a medium that exhibits a Gaussian conductivity. It is shown that, under certain circumstances, this applies to the ionosphere. The effects of different peak conductivities and Gaussian widths are examined, and a useful form for calculating transmission and reflection coefficients is presented.
The effect of strain on the dielectric constants of strained In0.7Ga0.3AsyP1−y films
Authors: Kim Hye-Rim , Kim Jeong Soo , Kim Hyung Mun , Choo Heung Ro , Kim Hong Man , Pyun Kwang Eui
Published: July 2002

We measured the dielectric constants of strained In0.7Ga0.3AsyP1−y (y=0.2, 0.4, 0.8, 1.0) and lattice-matched 1.32 μm In1−xGaxAsyP1−y thin films grown on InP substrates by metalorganic chemical vapor deposition. Measurements were performed by phase-modulated spectroscopic ellipsometry in the range of 0.76–4.9 eV. Our data bridge the gap between literature data in the near-infrared region and those in the visible-ultraviolet region. The critical point energies of strained In0.7Ga0.3AsyP1−y were compared with unstrained counterparts and were found to be shifted in accordance with the theory, which predicts that the compositional shift is compensated. Thus, the critical point energies of strained In1−xGaxAsyP1−y thin films of arbitrary composition can be estimated accurately and, conversely, the composition of strained In1−xGaxAsyP1−y thin films can be estimated by measuring their critical point energies, as for unstrained materials.
Enhanced flux pinning from CuO inclusions in Bi2Sr2CaCu2Oy crystals
Authors: Wang X. L. , Horvat J. , Liu H. K. , Dou S. X.
Published: July 2002

Bi2Sr2CaCu2Oy (Bi2212) crystals with CuO inclusions were grown on the surface of KCl flux. The density of CuO incorporations of 109/cm2 was similar to that for Y2BaCuOy in melt-textured YBa2Cu3Oy. The CuO inclusions are needlelike particles with diameter of less than 1 μm. Magnetization measurements show enhanced flux pinning at high magnetic field, compared to crystals without CuO.
Comparison of excimer laser recrystallized prepatterned and unpatterned silicon films on SiO2
Authors: Giust G. K. , Sigmon T. W.
Published: July 2002

The laser recrystallization of unpatterned and prepatterned silicon films on SiO2 is compared. For the prepatterned films, multiple-pulse laser irradiation at certain energy densities produces three well defined zones containing different microstructure. Two of these zones appear as bands along the edges of the prepatterned islands. The first zone, or “chill zone,’’ is found at the outer edge of the island, and consists of an ∼250-nm-wide band of heterogeneously nucleated fine grains. The second zone, or “columnar zone,’’ is found next to the chill zone, and is made up of large elongated grains, measuring about 1.5×0.5 μm, with their boundaries running perpendicular to the island edges. Finally, the third zone, or “equiaxed zone,’’ includes the remainder of the prepatterned island, and has a grain microstructure identical to the recrystallized unpatterned films. The creation and identification of these three zones for laser irradiated prepatterned Si films is presented. The laser conditions that create these zones, and the recrystallization mechanisms and resulting microstructure of each zone are presented in detail.
Formation and magnetic properties of novel compounds Tb3(Fe1−xVx)29
Authors: Han Xiu-Feng , Yang F. M. , Zhu J. J. , Pan H. G. , Wang Y. G. , Wang J. L. , Tang N. , Zhao R. W.
Published: July 2002

A systematic investigation of the structure and magnetic properties of novel compounds Tb3(Fe1−xVx)29 (x=0.033, 0.044, 0.056, and 0.061) has been performed. The lattice parameters and Curie temperatures are obtained. The saturation magnetization of Tb3(Fe1−xVx)29 decreases but the anisotropy field increases linearly with increasing V concentration at 4.2 K and room temperature. The spin reorientations of the easy magnetization direction of Tb3(Fe1−xVx)29 occur at around 160 K. A first order magnetization process of Tb3(Fe1−xVx)29 is observed with magnetic field in the range between 2.0 and 1.6 T at room temperature. The saturation magnetization of Tb3Fe29−yVy with a low V concentration at 4.2 K can be roughly calculated based on a combination of that of the Tb2Fe17 and TbFe12−yVy units in a ratio of 1:1.
Enhanced radiation shielding by space-charge fields in insulating slabs
Authors: Frederickson A. R. , Woolf S.
Published: July 2002

Space charge and the resulting electric fields accumulate in good insulators during irradiation. In high quality insulators the resulting large electric field will alter the trajectories of high energy electrons. The altered trajectories result in decreased flux of high energy electrons in some regions of material, thus providing enhanced shielding effectiveness. We experimentally and theoretically investigate the effect with high energy electron irradiation (0.7–2 MeV) of planar polymethylmethacrylate shields. For the slab shield cases which we investigated, the shielding effectiveness is enhanced by as much as a factor of 2. By allowing the electric field to extend into vacuum adjacent to the insulator, one obtains improved shielding effectiveness without adding mass.
Effects of hydrogen passivation on the electrical conduction in undoped polycrystalline silicon films
Authors: Saito Yoji , Aomori Masaru , Kuwano Hiroshi
Published: July 2002

The influence of the hydrogenation treatment on the conduction mechanism in the undoped polycrystalline silicon films near room temperature was investigated. The two current components are predicted from the temperature dependence of the conductivity in the films. We consider the hopping current in addition to the conventional thermionic (or drift) current. We have also found the hydrogenation induced increase phenomena of resistivity in the undoped polycrystalline silicon films and its activation energy, and qualitatively explain those by the decrease of the hopping current, which would relate to the band tail states, and that of the thermionic current, which would relate to the midgap states. From the analysis of the current components, it takes longer time for the passivation of the band tail states than that of the midgap states.
Determination of the nematic alignment and anchoring strength at the curved nematic–air interface
Authors: Slavinec M. , Crawford G. D. , Kralj S. , Z̆umer S.
Published: July 2002

A new method has been developed to determine the surface anchoring strength W and the tilt θt of the nematic director from the normal to a curved nematic–air interface. This method is based on the comparison of interference textures obtained by polarization microscopy experiments to numerical simulations of nematic liquid crystals within partially filled cylindrical tubes enforcing homeotropic anchoring. For the nematic liquid-crystal mixture ZLI 2860, we obtain θt=7°±1°, W=(1.5±0.5)×10−6 J/m2 at the nematic–tube and W>10−5 J/m2 at the nematic–air interface.
Thermal stability of W1−xSix/Si multilayers under rapid thermal annealing
Authors: Senderak R. , Jergel M. , Luby S. , Majkova E. , Holy V. , Haindl G. , Hamelmann F. , Kleineberg U. , Heinzmann U.
Published: July 2002

W 1−x Si x /Si multilayers (MLs) (x⩽0.66) were deposited onto oxidized Si substrates, heat treated by rapid thermal (RTA) and standard furnace annealing up to 1000 °C for 30 s and 25 min, respectively, and analyzed by various x-ray techniques and Rutherford backscattering spectrometry. W1−xSix/Si MLs are more stable the higher the value of x because the driving force for interdiffusion is suppressed by the doping; the temperature for complete interdiffusion increases from 500 to 850 °C as x increases from 0 to 0.66. The as-deposited MLs were amorphous. Their thermal stability increases with increasing x. The interface roughness is independent of x but increases with increasing RTA temperature. The reflectivity of W1−xSix/Si MLs is lower than that of W/Si because of lower optical contrast.
Search for new superconductors in the Y-Ni-B-C system
Authors: Knigge B. , Hoffmann A. , Lederman D. , Vier D. C. , Schultz S. , Schuller Ivan K.
Published: July 2002

We have searched for superconductivity in a wide variety of stoichiometries in the Y-Ni-B-C system, using Yx(NiB)Cy phase spread alloy thin films and the magnetic field modulated microwave absorption technique. The superconducting critical temperature (Tc) varies with the stoichiometry, showing the highest Tc for a Y/Ni ratio of 1/2, attributed to the YNi2B2C phase. We found no other superconducting phases with a Tc higher than 10 K. Furthermore, a search in YxNiB(C1−zNz)y and YxNiBNy phase spread alloys showed no superconductivity.
Ex situ hydrogen passivation effect of visible p-i-n type thin-film light-emitting diode characteristics
Authors: Lee Jong-Wook , Su Lim Koeng
Published: July 2002

The effect of ex situ hydrogen passivation process on the performance of visible hydrogenated amorphous silicon carbide (a-SiC:H)-based p-i-n type thin-film light-emitting diodes has been investigated. An ex situ hydrogen passivation process dramatically improved the device performance; that is, the threshold voltage decreased by about 5 V, the electroluminescence (EL) intensity increased by a factor of about 3, and the EL peak shifted toward a short wavelength from 700 to 600 nm, resulting in an increase of the brightness from 1 cd/m2 to 35 cd/m2. This improvement of device performance is caused by the passivation of interface states in the p/i and i/n interfaces as well as midgap states in the luminescent active intrinsic a-SiC:H layer by hydrogen atoms. A process time dependence of the ex situ hydrogen passivation effect on the device performance also has been studied.
Mobility measurement of large ions in air from a point-to-ring corona source
Authors: Giubbilini Pierluigi
Published: July 2002

The particular feature of the point-to-ring corona has been utilized in order to carry out measurements of the mobility of large positive ions by balancing their drift in a known electric field against a known air flow velocity. The experimental results have provided evidence of ionic-mobility values of the order of 10−6 m2/V s. These are typical values of the so-called intermediate ions which normally consist of some 4000 water molecules surrounding singly charged ionized atoms such as H+ and Na+.
Single-phase single-electron digital circuits
Authors: Ancona M. G.
Published: July 2002

An approach to synchronous single-electron digital circuits is described in which only one clocking signal is required. Such designs may facilitate the development of clock distribution methods with the excellent scaling properties needed if a practical single-electronics technology is ever to be realized.
Dynamic compaction of powders by an oblique detonation wave in the cylindrical configuration
Authors: Carton E. P. , Verbeek H. J. , Stuivinga M. , Schoonman J.
Published: July 2002

A new method has been applied to dynamically compact ceramic powders in the cylindrical configuration. In this method, a converging oblique detonation is used instead of the sliding detonation used in the standard method. The oblique detonation is generated by a configuration using two explosive layers. X-ray flash photographs have been made that show the detonation and shock fronts in both the standard and new configuration. In the present article, the shock wave and particle velocities in the B4C powder have been calculated using the shock and detonation angles obtained from the photographs in combination with the measured detonation velocity. In the two-layer configuration, the pressure applied to the powder was increased by a factor of 3.5 compared to the one-layer configuration, in agreement with calculations. The working principle of the two-layer configuration is discussed and compared with a computer simulation of the process.
Magnetic properties and magnetic phase diagram of frustrated Co1−xFexPt3 compounds
Authors: Kim T. H. , Cadeville M. C. , Dinia A. , Rakoto H.
Published: July 2002

The investigation of the magnetic properties of the pseudobinary Co1−xFexPt3 L12 ordered compounds resulting from alloying ferromagnet CoPt3 and frustrated antiferromagnet FePt3 is reported. The magnetic phase diagram of this system shows the presence of a pure spin glass phase that separates the ferromagnetic region from the antiferromagnetic one. On the Co-rich side (x<0.6), two re-entrant spin glass phases are found to emerge at low temperature in the ferromagnetic region. On the iron-rich side, an antiferromagnetic region with two antiferromagnetic [12 120] and [1200] structures is observed for 1⩾x⩾0.8. This magnetic phase diagram is discussed comparatively with the previously determined (Fe–Mn)Pt3 and (Co–Mn)Pt3 phase diagrams. The randomness of the average exchange interaction is suggested to arise from a competition between the three dominant magnetic interactions JCoCo, JFeFe, and JCoFe of 3d atoms in sites of second nearest neighbors in the L12 structure.
Spin glass behavior in some Fe–Mn–Al disordered alloys
Authors: Zamora Ligia E. , Pérez Alcázar G. A. , Rodrı́guez V. F. , Tabares J. A. , Bohórquez A.
Published: July 2002

In this work, we report an ac susceptibility study of Fe0.5Mn0.2Al0.3, Fe0.5Mn0.1Al0.4, and Fe0.225Mn0.375Al0.40 disordered alloys. All the samples exhibit only one well defined peak near 58, 18, and 31 K, respectively. When the frequency of the ac field increases, the measured intensities of the peaks decrease and the maxima shift to higher temperatures, and when the dc field increases the intensity of the peaks decreases. This dependence of the position and intensity of the peaks on the field and frequency is evidence of the spin glass character of the transitions in these alloys. Mössbauer spectra at different temperatures were performed for the sample with 30 at. % Al and the plot of the adjusted mean hyperfine field versus temperature shows a kink at 53 K which is further evidence that this sample shows spin glass behavior.
Study of the magnetic and magneto-optical properties of [110]-oriented Fe3O4/NiO superlattices
Authors: Stoyanov P. , Gottschalk A. , Lind D. M.
Published: July 2002

The magnetic behavior of a set of [110]-oriented single crystalline Fe3O4/NiO superlattices was studied by SQUID magnetometry and by magneto-optical Kerr-effect (MOKE) measurements. Samples for this study were grown on MgO substrates by means of plasma-assisted molecular beam epitaxy with the NiO layer thickness kept constant, while the Fe3O4 layer thickness and the number of bilayers were varied in such way as to preserve the total Fe3O4 thickness throughout the entire set. The structural ordering was studied by x-ray diffraction and reflection high energy electron diffraction. The growth mode was single crystalline, but with rough interfaces. The hysteresis profiles vary with the Fe3O4/NiO thickness ratio; with thinner Fe3O4 layers the degree of influence of the high-anisotropy antiferromagnet (NiO) spin system over that of the ferrimagnet (Fe3O4) increased. The optical constants of the substrate and the component layers at 632.8 nm wavelength were obtained in two steps by unconstrained and constrained optimization algorithms based on the Fresnel equations and ex situ ellipsometric measurements. These optical constants were found to differ by a small but distinct amount from the available standard values. The magneto-optical constant (also at 632.8 nm) of the Fe3O4 layer was determined from longitudinal and polar Kerr effect measurements using one of the existing matrix methods and was found to be a direction-dependent function of the Fe3O4 layer thickness.
Magnetic dissipation imaging (abstract)
Authors: Liu Y. , LeBlanc P. , Grütter P. , Dürig U.
Published: July 2002

We report the first direct measurement of local magnetic dissipation by magnetic force microscopy (MFM). A variation in dissipation of less than 10−17 W can be observed. This allows the determination of the strength of pinning sites and the variation in domain wall dampening on a sub-100 nm scale. We use a standard thin film coated Si3N4 MFM force sensor vibrated exactly at resonance. When close to the sample, the magnetic tip exerts a highly localized alternating magnetic field. Magnetic energy dissipation in the sample leads to dampening of the cantilever oscillation. The frequency, phase, and amplitude of the cantilever oscillation is measured with a dedicated phase-lock-loop circuit. The change in driving signal amplitude is directly proportional to the energy dissipation if the drive signal phase is constant. Constant force gradient and dissipation images are acquired simultaneously. By changing the tip–sample spacing, the magnitude of the tip magnetic field influencing the sample can systematically be varied. We demonstrate the potential of this technique by imaging local variations of dissipation in 4 nm thin sputtered Co films with Hc=178 Oe and in 30 nm Permalloy samples with Hc=2 Oe. In both cases a variation on a sub-100 nm scale with strong correlations between the simultaneously measured domain structure and the dissipation images is observed. As expected, dissipation is strongly dependent on the magnitude of the tip field. We also observe that the magnitude of the dissipation depends strongly on the sign of the magnetic interaction. The dissipation observed at Néel walls with attractive tip–sample interaction is larger than the dissipation at repulsive walls.
Magnetic domain imaging with low energy electron microscopy (abstract)
Authors: Kachel T. , Gudat W. , Koziol C. , Schmidt Th. , Lilienkamp G. , Bauer E. , Altman M.
Published: July 2002

Photoelectron microscopy has recently been developed into a strong tool for the investigation of surfaces of solids. The use of electron energy analyzers or synchrotron radiation tunable to particular electron excitation edges provides high element sensitivity of the method. In addition, when circularly polarized soft x rays are used, the magnetic circular dichroism effect offers the possibility of imaging magnetic domain structures in an element specific way.1234 The low energy electron microscope (LEEM) in combination with the PM 3 monochomator at BESSY which supplies circularly polarized soft x rays has been used for this purpose. The LEEM was equipped with an electrostatic energy analyzer providing an energy resolution of the photon-excited electrons of better than 500 meV. The lateral resolution of the LEEM instrument was shown earlier to reach down to 10 nm in the electron excitation mode. In the case of synchrotron radiation excitation the resolution depends largely on the brightness of the photon beam. At the BESSY TGM 5 undulator beamline which supplies linearly polarized light we have achieved a resolution of 30–40 nm in chemically sensitive photoelectron microscopy. At the PM 3 beamline using circularly polarized soft x rays at about 700 eV photon energy the resolution was 200–300 nm. In the chemically and magnetically sensitive mode we have studied a stainless steel sample that showed locally ordered grains with interesting magnetic domain structures. On the basis of LEEM in the electron impact low energy electron diffraction (LEED) mode (= LEED microprobe) it was possible to correlate the domain structures to the underlying bcc Fe lattice orientation. Exposure to external magnetic fields and heat treatment had a strong influence on the magnetic structure.
Barkhausen effect in steels and its dependence on surface condition
Authors: Parakka A. P. , Jiles D. C. , Gupta H. , Zang M.
Published: July 2002

Micromagnetic Barkhausen signals from magnetic materials originate from the discontinuous changes in magnetization under the action of a changing applied magnetic field. Barkhausen emissions that are detected by a sense coil come predominantly from a surface layer. In iron based materials this layer is about 500 μm thick. The Barkhausen signal is affected by changes in material microstructure and the presence of residual stress, since these affect the dynamics of domain wall motion. The selective attenuation of high frequency components of the Barkhausen signal due to eddy currents in electrically conducting materials is used to evaluate changes in material condition at different depths inside the material. Barkhausen measurements on specimens subjected to different thermal treatment during surface conditioning procedures are presented. Also presented for comparison are analysis of the material condition using x-ray diffraction for assessment of residual stress, and microhardness measurements which evaluate the surface microstructure condition. The results show that Barkhausen emissions can be utilized to evaluate changes in the surface condition of materials.
Micromagnetics at submicron dimensions (abstract)
Authors: Slonczewski J. C.
Published: July 2002

We represent the state of a circa 10-nm thick submicron dimensioned magnetic film with a superposition of two-dimensional (2D) magnetic pseudovortices. The effective intervortex exchange-stiffness potential and local magnetization angle at a complex distance z=x+iy from the kth vortex center are given by the real and imaginary parts respectively, of the function −wklnz. Each of the four corners of the rectangle has a stationary quarter vortex with negative winding (wk=−1). Two mobile semivortices with winding wk=+1 and N and S magnetic poles lie at general positions X1 and X2, respectively, along edges of the rectangle. The approximate boundary condition of vanishing M-component normal to each edge is satisfied by repeated reflections which generate a periodic extension of this vortex array to a lattice filling all of a 2D space. The internal energy V(X1,X2) is principally composed of the inter vortex exchange stiffness. Given this function, numerical evaluation of the integrated moment m=m(X1,X2) provides the functional dependence of V on m as parametrized by (X1,X2). The function V(X1,X2) has four equal minima representing states with the N and S vortices located at diagonally opposite corners, in agreement with direct numerical simulations. Therefore, the predicted hysteresis behavior of our vortex model has significantly more complex transitions than those of a uniaxial single-domain particle having only two minima. Our employment of but two variables, rather than the continuum of straightforward micromagnetics, makes possible a more insightful analysis of the smallscale structures used in storage and memory.
Epitaxial growth of and silicide formation in Fe/FeSi multilayers
Authors: Dekoster J. , Bemelmans H. , Degroote S. , Moons R. , Verheyden J. , Vantomme A. , Langouche G.
Published: July 2002

The structural properties of multilayers consisting of Fe layers separated by Si or FeSi layers grown with molecular beam epitaxy on MgO(001) and Si(111) are reported. Rutherford backscattering and ion channeling are used to determine the crystallinity of the layers. We find evidence for epitaxy, alloying effects, and structural coherence. Conversion electron Mössbauer spectroscopy is utilized to investigate the silicide formation in the spacer layer of Fe/FeSi multilayers and at the interface of Fe/Si layers. The silicide formed in Fe/FeSi multilayers is characterized by a broad single line Mössbauer resonance which is characteristic for the metastable CsCl–FeSi phase. For Fe/Si multilayers the Mössbauer results indicate that FeSi compounds with clearly other hyperfine parameters than the CsCl phase are formed in the spacer.
Evidence for “loose spins” in epitaxial Al/Fe/Al
Authors: Gutierrez C. J. , Selestino R. , Mayanovic R. A. , Prinz G. A.
Published: July 2002

Polarization-dependent Fe K-edge x-ray absorption fine structure measurements of an Al/Fe/Al(001) trilayer reveal a small tetragonal distortion of the Fe sites with c=2.863 Å (normal to the film plane) and a=2.874 Å (in the film plane). This tetragonal distortion is consistent with the formation of Fe1−xAlx alloys in the vicinity of the roughened Fe–Al trilayer interfaces, and agrees with grazing incidence x-ray reflectivity and magnetometry measurements of the trilayer. The deduced alloyed/roughened interfacial regions are the likely source of Fe “loose spins” as recently suggested by Slonczewki’s biquadratic coupling model for the epitaxial Fe/Al/Fe system.
Humidity effect on friction/stiction and durability of head-disk interface with polar perfluoropolyether lubricant
Authors: Zhao Zheming , Bhushan Bharat
Published: July 2002

Drag and contact start and stop (CSS) tests are performed at different relative humidities to understand the effect of humidity on friction/stiction and durability of thin-film disks lubricated with a polar perfluoropolyether lubricant. Coefficient of friction and stiction increases above a certain relative humidity (RH). Durability increases with an increase of relative humidity and then decreases with a further increase of humidity after having reached a maximum. Humidity effect on friction/stiction and durability is found most severe at about 80% RH. Adsorbed water may displace and/or permeate into the lubricant film and result in a nonuniform liquid film.
Critical behavior of cubic magnetostrictive materials under stress
Authors: Cullen J. R. , Hathaway K. B. , Clark A. E.
Published: July 2002

Critical points and lines in magnetic field space define the boundaries of different magnetization states between which the magnetization may “jump,” leading to hysteresis. We calculate the changes in these boundaries due to magnetoelastic coupling to applied stresses, and obtain the critical stresses required to eliminate jumping in specific cases. These results may provide a way of reducing or eliminating hysteresis in large magnetostriction materials.
A Mössbauer spectral study of the Nd6Fe13X compounds where X is Si, Cu, Ag, and Au
Authors: Hautot Dimitri , Long Gary J. , Grandjean F. , de Groot C. H. , Buschow K. H. J.
Published: July 2002

The Mössbauer spectra of Nd6Fe13X, where X is Si, Cu, Ag, and Au, have been measured between 85 and 435 K. An analysis of the spectra of Nd6Fe13X, where X is Cu, Ag, and Au in terms of five sextets, indicates that the iron moments lie in the basal plane of the unit cell. The assignment of the five sextets to the five magnetically inequivalent sites in the structure is based on a correlation between the isomer shift and the Wigner–Seitz cell volume for all iron sites, between the isomer shift and the hyperfine field for each site, and the relationship between the hyperfine field at a given iron site and its number of iron near-neighbors. An analysis of the spectra of Nd6Fe13Si reveals that a high temperature magnetic phase, with its moments parallel to the c axis, coexists between 295 and 85 K with a low temperature magnetic phase, with its moments oriented in the basal plane. Hence, Nd6Fe13Si shows a continuous magnetic spin-reorientation from axial towards basal alignment upon cooling.
Thermal expansion and magnetostriction in colossal magnetoresistance mixed valence manganites (abstract)
Authors: De Teresa J. M. , Ibarra M. R. , Algarabel P. A. , Marquina C. , Blasco J. , Garcia J. , del Moral A.
Published: July 2002

Structural aspects are closely related to the large spontaneous and field-induced magnetic and magnetogalvanic effects in mixed valence manganites. Local distortions are the source of an extra contribution to the thermal expansion. These were associated with a charge localization process.1 The existence of ferromagnetic order in these compounds favors the carriers mobility and, as a consequence, produces unexpected magnetovolume effects.2 We report thermal expansion measurements within the temperature range 4–800 K and magnetostriction up to 15 T in the series (R1−yRy)1−xCaxMnO3 (R=La, Nd and R′=Y, Tb). We have found completely unusual volume magnetostriction at temperatures at which the system is in the insulator state (paramagnetic, antiferromagnetic, spin-glass states). These results give a deep insight into the mechanism responsible for the colossal magnetoresistance and reveal these experimental techniques as an excellent tool to follow the spontaneous and field-induced localization and delocalization processes.
Ab initio calculations of the “giant” magnetoresistance in uranium intermetallics (abstract)
Authors: Richter Manuel , Antonov Victor N. , Zahn Peter , Oppeneer Peter M. , Diviš Martin , Perlov Alexander Ya. , Yaresko Alexander N. , Mertig Ingrid , Halilov Samed V. , Eschrig Helmut
Published: July 2002

Based on the coherent electronic structure of the ideal crystal, the “giant” magnetoresistance (GMR) of UNiGa and U2Pd2X (X=In, Sn) at the field-induced transition from the antiferromagnetic ground state to the ferromagnetic state is calculated using linear transport theory. Assuming that the scattering is well represented by a single averaged relaxation time, good agreement with experimental data is obtained for the GMR of UNiGa. The effect can be understood from topological changes of particular Fermi surface sheets at the magnetic transition, bringing about conductivity changes of a factor of 2. No experimental data are available for the high-field resistivity of U2Pd2X. Here, in contrast to UNiGa, the Brillouin zone is invariant under the metamagnetic transition. Nonetheless, conductivity changes up to a factor of 2 are found, again caused by changed connectivity of the Fermi surface. Moreover, we predict the possibility of an inverse GMR effect for this system without introducing spin-dependent scattering. The latter is shown to have minor influence due to strong spin–orbit coupling.
Micromagnetic simulation of the relaxation processes taking place in systems with distributed properties
Authors: González J. M. , Smirnov-Rueda R. , González J.
Published: July 2002

We have examined, in terms of the micromagnetic approach, the thermally activated demagnetization behavior of a 1D model polycrystalline material having distributed local easy axes directions. Our analysis was based on the evaluation of the time dependence of the magnetization under different constant demagnetizing fields. From our results, we conclude that (i) thermally activated demagnetization proceeds through a nucleation-propagation mechanism, (ii) the time evolution of the magnetization can be well described in terms of ln(t+T0) laws, and (iii) the activation length (the 1D equivalent of the activation volume) gives a measure of the thickness of the walls limiting the regions reversed during the relaxation process.
Modeling of Barkhausen noise in magnetic core material: Application of Preisach model
Authors: How H. , Sun L. , Vittoria C.
Published: July 2002

The Preisach model is utilized to model Barkhausen noise in magnetic core materials. Barkhausen noise is generated each time the magnetization goes through a sudden change at a local site in the core material. In this article we examine the relationship between the shape of magnetization hysteresis loops to details of Barkhausen noise levels or excitations. On the basis of hysteresis loops alone it may be possible to profile the noise spectrum of a magnetic core.
Efficient approximate solutions to micromagnetic problems
Authors: Arrott A. S. , Templeton T. L.
Published: July 2002

The sixfold integral of magnetostatics ∫∫∫∫∫∫ div M{r}div M{r′}/|r′−r|d3r′ d3r is replaced by a local pseudo interaction λ2∫∫∫ div2 M{r}d3r in the expression for the micromagnetic energy. A magnetic configuration M{λ,r} is found by minimization of this micromagnetic energy for each choice of λ2. The sixfold integral is then evaluated for a few values of λ2. These are used to interpolate between those values to find a constrained minimum of the micromagnetic energy with the sixfold integrals. The method is applied to the description of the intersection of a Bloch wall with the surface of a thick crystal for magnetically soft materials characterized by large saturation magnetization Ms and small uniaxial anisotropy Ku; that is, Ms2>Ku.
Creep-induced magnetic anisotropy and magnetostriction in a nanocrystalline Co based alloy
Authors: Murillo N. , González J. , Blanco J. M. , Valenzuela R. , González J. M. , Echeberrı́a J.
Published: July 2002

Co rich amorphous alloy (Vitrovac® 6025) ribbons have been current-annealed under a tensile stress of 500 MPa, applied along the ribbon axis. This results in a strong, creep-induced magnetic anisotropy with a hard ribbon axis, which increases as current density J increases. For high J, the magnetostriction constant showed a two component behavior as a function of measuring stress; one component for low stress (σ<100 MPa) and another one for high stress (σ>100 MPa). These results are interpreted in terms of structural relaxation (low J) and nanocrystallization (high J). Magnetostriction measurements appear as a very sensitive characterization tool.
Magnetic circular versus linear dichroism effects: A case study at the Fe M2,3 edge (abstract)
Authors: Höchst Hartmut , Rioux Dennis , Zhao Dai , Huber David
Published: July 2002

Magneto-optical measurements are strongly dependent on the polarization of the radiation as well as the interaction geometry of the light with respect to the relative orientation and direction of the magnetization M. In an effort to identify the different angular and spectral contributions and to select the preferred experimental setup for magneto-optical measurements, we performed magnetic circular dichroism (MCD) and magnetic linear dichroism (MLD) measurements around the Fe M2,3 transition. The MCD experiments were performed by measuring the difference between the reflected intensities of left and right circularly polarized soft x-ray radiation. While for the MCD experiments, the magnetization was kept constant, it was modulated between M+ and M− for the MLD spectra. We used a quadruple reflection polarizer that was tuned to act as a λ/4 phase shifter for the MCD measurements and as a linear polarizer for the MLD experiments. The experiments confirm our model calculations for longitudinal and polar MCD and transverse MLD using a previous determined energy-dependent dielectric tensor ε(ω). The outcome of our experiments has consequences for most MCD experiments performed with Pcirc<1 in combination with mixed geometry. Such a configuration could severely alter the quantitative MCD analysis due to the strong MLD contribution.
Magnetoelastic and pressure effects at the ferro–antiferromagnetic transition in Hf1−xTaxFe2−y alloys (abstract)
Authors: Morellon L. , Algarabel P. A. , Ibarra M. R. , Arnold Z. , Kamarád J.
Published: July 2002

Magnetostriction measurements using high pulsed magnetic field up to 14 T and thermal expansion measurements under hydrostatic pressure up to 10 kbar have been performed in the Hf1-xTaxFe2−y alloys with x=0.17 and 0.15 and y=0.02. These compounds have a first-order magnetic phase transition from an antiferromagnetic (AF) high temperature state to a ferromagnetic (F) low temperature state at TAF–F=245 and 290 K, respectively. This transition is accompanied by a volume expansion from the low volume AF state to the high volume F state of ΔV/V≈0.56% and 0.38% for x=0.17 and x=0.15, respectively. The hydrostatic pressure significantly decreases the temperature of the AF–F transition whereas the thermal expansion anomaly is becoming more pronounced. The dependence of TAF–F on pressure follows a quadratic behavior and TAF–F reaches the value of 106 K at 10.5 kbar for x=0.17. In the search for high magnetostrictive materials, we have found in these alloys a giant value of the volume magnetostriction (ω≈0.6% for the x=0.17 compound) at a moderate applied magnetic field within the AF phase near room temperature, making of these alloys potential candidates for magnetostrictive transducers. All the experimental results will be explained assuming the existence of two different states as has been proposed by Moruzzi.1
Temperature dependence of the macroscopic ferri–ferromagnetic transition in amorphous Y–Co/Gd–Co bilayers
Authors: Yonamine T. , Tufaile A. P. B. , Santos A. D. , Souche Y.
Published: July 2002

We studied the temperature dependence of the macroscopic ferri–ferromagnetic transition in amorphous Y–Co/Gd–Co bilayers. The samples were produced by sputtering, and characterized by vibrating sample magnetometer and transverse magneto-optical Kerr effect at low temperature. From a model of the unusual shaped domain wall (DW) at the interface of the bilayer, we determined the temperature dependence of the thickness δ and relative position Δ of the DW and, also the exchange constant A.
Anomalous behavior of the thermopower and temperature derivative of resistivity near the spin reorientation transition in Er2Fe14B
Authors: Amado M. M. , Pinto R. P. , Braga M. E. , Rogalski M. S. , Sousa J. B.
Published: July 2002

Experimental observation of the first-order nature of the spin reorientation transition in polycrystalline Er2Fe14B through high resolution resistivity, thermopower and Fe57 Mössbauer data is reported. Both a steplike decrease in resistivity and an increase in thermopower over a very narrow temperature interval around 323 K indicate a discontinuous spin reorientation transition. This is consistent with the change in sign of the quadrupolar shifts at all Fe sites at this temperature, derived from the Mössbauer spectra, which are indicative for the transition from planar to uniaxial anisotropy with increasing temperature. The symmetrical lineshape of the sharp singularity recorded in the temperature derivative of resistivity provides unambiguous evidence for the first-order nature of the spin reorientation.
Effects of Ar bombardment on magnetic properties of Fe films deposited by double-ion-beam sputtering
Authors: Iwatsubo S. , Takahashi T. , Naoe M.
Published: July 2002

The microstructure and magnetic properties of polycrystalline Fe films have been investigated in detail by controlling the condition of ion-beam sputtering with an Ar bombardment with a constant ratio of arrival rate of Fe to Ar. To control the Fe crystallite size, Fe films have been deposited at an Ar bombardment voltage VA in the range of 80–2000 V with the condition that the ratios of the arrival rate RA (atoms of Fe/atoms of Ar) were 1 to 1 (RA of 1) and 1 to 0.1 (RA of 0.1). Fe films with excellent soft magnetic characteristics for 4πMs of about 21.5 kG and HC of 2.5 Oe were deposited on the substrate bombarded by Ar ions with VA of 200 V at Rs of 1 and 400 V at RA of 0.1. The Ar bombardment had the two effects of raising the local temperature of the film surface and decreasing the Fe crystallite size. The orientation of crystals in the films may be related to the bombardment energy and amount of Ar ions. The high-energy bombardment formed a mixing layer between the deposited film and the surface of the substrate. These results imply that Ar bombardment by the proper energy and amount of Ar ions assists in improving the soft magnetic properties in the films.
Sputter epitaxy of cerium yttrium iron garnet films on neodymium gallium garnet substrates
Authors: Okamura Y. , Kawakami T. , Yamamoto S.
Published: July 2002

We present the experimental results on the in situ epitaxial growth of cerium substituted yttrium iron garnet films on three different single crystalline substrates by use of the magnetron sputtering, in particular, paying attention to the films deposited on the neodymium gallium garnet. Intrinsic properties of the grown films such as lattice constant, specific Faraday rotation, and hysteresis have been measured. We have found that the sign of the lattice mismatching between the film and the substrate is important for the enhancement of the magneto-optic effect, and the lattice matching is attainable by changing the oxygen gas flow rate while growing the crystal.
Micromagnetic configurations of martensite in Fe-Ni alloys
Authors: Hirohata Atsufumi , Miyajima Hideki
Published: July 2002

The magnetic domain structure and the surface relief of the martensite in Fe1−xNix alloys were investigated by using both noncontact atomic force microscopy (NC-AFM) and magnetic force microscopy (MFM). In the Ni compositional range 0.25<x<0.29, the lathlike martensites and the complex magnetic domains were formed, while the lenslike martensite and the stripe domain were observed in 0.29<x<0.34. It is found that the magnetic domain structures on the martensites are connected with magnetoelasticity due to residual stress near the mid-rib.
Structure and magnetic properties of Tm2Fe17−xGax compounds
Authors: Shen Bao-gen , Cheng Zhao-hua , Liang Bing , Gong Hua-yang , Wang Fang-wei , Tang Hong , Cao Lei , de Boer F. R. , Buschow K. H. J.
Published: July 2002

Crystal-structure studies on Tm2Fe17−xGax (x=0, 1, 2, 3, 4, 5, 6, 7, and 8) compounds have shown that the prepared samples are single phase with the 2:17-type structure. Both the unit-cell volume and the saturation magnetization at 1.5 K decrease linearly with increasing Ga content. The Curie temperature is found to increase with increasing x; it goes through a maximum value of 485 K at about x=3 to lower values and then it rises again. The Tm2Fe17−xGax compounds exhibit a spin–reorientaiton transition at low temperature. X-ray diffraction measurements on magnetically aligned Tm2Fe17−xGax powders show that the compounds with x⩽6 have the easy-plane type of magnetic anisotropy, whereas the compounds with x⋚7 exhibit the easy c-axis type of magnetic anisotropy at room temperature.
Electron paramagnetic resonance study of amorphous silicon produced by Kr+ ion implantation into silicon
Authors: Rakvin B. , Pivac B. , Reitano R.
Published: July 2002

A detailed analysis of the electon paramagnetic resonance line shape was performed on amorphous Si samples obtained by Kr+ ion implantation. The Lorentzian character and behavior upon annealing was explained via a strong exchange interaction, leading to a cluster model for the spin density distribution. The saturation measurements are shown to be a convenient method to study structural changes caused by thermal annealing. The spin density distribution (as described with the cluster model) imposes a clear difference between amorphous Si material obtained by ion implantation and one obtained by evaporation and/or chemical vapor deposition.
Magnetic ordering in perovskites A1−xMnO3+y (A=La, Bi, rare earth ion) (abstract)
Authors: Troyanchuk I. O. , Kasper N. V. , Szymczak H. , Nabialek A.
Published: July 2002

In order to clarify the mechanism of exchange interactions in orthomanganites with perovskite structure a magnetic study of parent compounds as a function of stoichiometry has been made. It was shown that the LaMnO2.99 is a weak ferromagnet with TN=147 K while LaMnO3.13 and La0.9MnO3.05 are ferromagnets with TC=160 and 240 K, respectively. The magnetic data indicate that the mixed magnetic state involving ferro- and antiferromagnetic domains is realized in the intermediate range of oxygen content. The RMnO3+y (R=Nd, Sm, Eu, Gd) are inhomogeneous antiferromagnets. The temperatures of start of magnetic moments freezing inside ferromagnetic clusters depend slightly on stoichiometry and for y∼0 are equal 83, 65, 47, and 22 K, respectively. The coercive field for LaMnO3 is 6 kOe at 4.2 K while that for EuMnO3 is much higher—26 kOe. It is worth noting that the Neel temperatures of RMnO3 (R=Eu, Gd, Tb, Dy) are estimated to be about 40 K independently of the type of rare-earth ion. Magnetic moments of Gd, Tb, and Dy in the rare-earth sublattice are antiferromagnetically ordered below 6–7 K. Applying external fields induces the antiferromagnet–ferromagnet transition in rare-earth sublattice. Hcr at 2 K for RMnO3 (R=Gd, Tb, Dy) are measured to be about 5, 12, and 10 kOe, respectively. In contrast to rare-earth compounds, the BiMnO3 is ferromagnet below 98 K. The deviation from stoichiometry as well as replacement of Bi ions by Sr, Ca, or La ions leads to the suppression of the long-range ferromagnetic order. Magnetic properties are discussed in terms of super exchange interactions between manganese ions via oxygen taking into account the 3d-orbital ordering that occurs in LaMnO3 and TbMnO3 at 400 and 1200°C, respectively.
In-situ ellipsometric control of magnetic multilayer deposition (abstract)
Authors: Gao Xiang , Heckens Scott , Woollam John A.
Published: July 2002

Correct determination of layer thicknesses on a subnanometer scale is crucial for studies of giant magnetoresistance, magneto-optical (MO) Kerr rotation, magnetic interlayer coupling, and other magnetic properties of metallic multilayers. Some structures such as [Co/Ni] and [Co/Pt] with fewer than 20 repeats are difficult to be analyzed by x-ray diffraction (XRD) due to too little material. In this work, in-situ spectroscopic ellipsometry (in-situ SE) is used to precisely determine the optical constants undisturbed by oxidation, and the growth rates of different metal films deposited in a sputtering chamber. In-situ SE determines both the constant and continuously changing growth rates during deposition of individual layers. SE data were also taken during multilayer thin-film growth, from which we determine the individual layer thicknesses in the superlattice to a fraction of an angstrom. The in-situ SE data and ellipsometric analysis of [Co/Au] and [Co/Ni] multilayers on thick gold-coated silicon, and [Co/Pt] multilayers with a Pt underlayer are presented. Less than a few percent difference was found by comparing the XRD thickness results to the in-situ SE thickness results. In-situ SE permits studies of oxidation kinetics, important because oxidation strongly influences both the magnetic and MO results. Specifically, spectroscopic MO Kerr rotation, ellipticity, and figure of merit of [Co/Ni] and [Co/Pt] multilayers with different repeat structures, with and without capping layers are reported covering the spectral range from ultraviolet to near infrared.
Molecular dynamics method to itinerant magnets with complex magnetic structure
Authors: Akbar S. , Kakehashi Y. , Kimura N.
Published: July 2002

A molecular dynamics method which allows us to determine the magnetic structures of itinerant magnets with a few hundred atoms in a unit cell has been developed on the basis of the functional integral method. The method yields the generalized Hartree–Fock approximation at the ground state, and describes the finite temperature magnetism accompanied by the second order phase transition. The results for fcc transition metals with the use of 108 atoms in a unit cell show a complex antiferromagnetic (AF) structure for the d electron number nd=6.0, the first-kind AF for nd=6.2, the helical structure with Q=(0,1/3,1)2π/a for nd=6.4, the helical structure with the same Q but with modulated amplitudes of local moments for nd=6.6. A helical structure with Q=(0,1/3,2/3)2π/a is obtained for γ-Fe.