bluuebunny/crossref_metadata_2025 huggingface dataset:
Spin wave excitations of single domain walls in orthorhombic ferromagnets
Authors: Kulagin N. E. , Popkov A. F. , Synogach V. T. , Dötsch H.
Published: July 2002

A ferromagnetic crystal with cubic and induced orthorhombic and uniaxial anisotropies is considered. The hard uniaxial anisotropy axis is parallel to the [110] direction, the hard orthorhombic axis parallel to the [1̄10] direction. Localized spin waves propagating along a single domain wall in such materials are analyzed by numerical solution of the Landau–Lifshitz and magnetostatic equations. The spin wave spectra are calculated for propagation directions either perpendicular or parallel to the direction of the magnetization in the two adjacent domains. There exist critical combinations of magnetic anisotropy constants for which the uniform Bloch wall becomes unstable before the Neel wall is preferred. In such parameter regions Goldstone modes show a gap in the wave number and a loop of the dispersion branch for the case of perpendicular propagation. This behavior is very similar to that of hydrodynamic waves excited in stratified shear flows. The existence of negative energy waves and the appearance of a Kelvin–Helmholtz instability are to be expected for spin waves propagating along an initially plane domain wall in the absence of dissipation. All spectra for perpendicular propagation are asymmetric with respect to wave vector inversion. They also contain the unidirectional Gilinskii-type mode which has a finite frequency at zero wave number. This activation frequency coincides with the frequency of the bottom of the bulk spin wave manifold for propagation parallel to domain magnetizations. Measurements of resonant excitations of single domain walls in bismuth-substituted garnet films with in-plane magnetization are presented. The resonances are observed in the frequency range from 50 to 1500 MHz. They are qualitatively discussed on the basis of the developed theory.
Precise measurement of dielectric anisotropy in ice Ih at 39 GHz
Authors: Matsuoka Takeshi , Fujita Shuji , Morishima Shigenori , Mae Shinji
Published: July 2002

The dielectric permittivities parallel and perpendicular to the c axis (optic axis) of ice Ih were measured using an open resonator at 39 GHz in the temperature range 194–262 K. The dielectric anisotropy in ice at microwave frequencies is important for understanding remote sensing data in polar regions, obtained by ice radar and satellite-born microwave radar and radiometer. The measured samples were natural single-crystal ice collected from Mendenhall Glacier, Alaska. A very precise measurement was achieved by detecting two resonant peaks, one from the ordinary component and the other from the extraordinary component, simultaneously, from one sample. The real part of dielectric anisotropy, Δε′=ε∥c′−ε⊥c′, at 39 GHz was 0.0339±0.0007 (1.07%±0.02%) at 252 K and slightly depended on temperature. Reference measurements at 1 MHz using parallel plate electrodes were also carried out. The measured dielectric anisotropy at microwave frequencies agrees very well with the value at 1 MHz. The absolute values of ε∥c′ and ε⊥c′ at 39 GHz were, respectively, smaller than those at 1 MHz and the difference was about 0.044 at 252 K. The results suggest that a small dispersion exists between GHz and MHz frequencies, but there is no frequency dependence in the value of anisotropy.
Critical behavior of the resistivity in YCo12B6 and GdCo12B6 intermetallics
Authors: Lee Seung Pyo , Kim Chul Koo , Nahm Kyun , Mittag M. , Jeong Yoon Hee , Ryu Chang-Mo
Published: July 2002

The electrical resistivity ρ of the intermetallics YCo12B6 and GdCo12B6 has been measured in the temperature range of 80 K<T<250 K, which embraces the second-order magnetic phase transition. From the temperature derivatives of ρ(T), the critical exponent α of the specific heats has been determined. We found that the values of α are typical of a Heisenberg ferromagnet. The temperature derivatives of ρ(T) are compared with the specific heat measurements. Also, the physical implications of the results are discussed.
Transmission electron microscopy analysis of a multiple quantum wire structure fabricated by dislocation slip
Authors: Ressier L. , Peyrade J. P. , Vieu C.
Published: July 2002

Dislocations are used as “atomic saws’’ to cut a 5 nm GaAs quantum well into a multiple quantum wire structure. The direct observation of these cuts in the volume, was performed by transmission electron microscopy, using cross section specimens, thinned perpendicular to the quantum wire axis by a highly localized preparation technique. This special thinning procedure, involving electron-beam lithography and reactive ion etching, allowed us to realize a statistical analysis of the distances between neighboring cuts and the heights of cuts. This dimensional analysis revealed the formation of coupled quantum wires with a width of 18±9 nm and free from any lateral roughness on 100 nm lengths.
Heteroepitaxial properties of Si1−x−yGexCy on Si(100) grown by combined ion- and molecular-beam deposition
Authors: Jacobsson Harald , Xiang Joan , Herbots Nicole , Whaley Shawn , Ye Peihua , Hearne Sean
Published: July 2002

The heteroepitaxial growth of the new ternary, group-IV, semiconductor material, Si1−x−yGexCy on Si(100), has been investigated. The epitaxial quality of Si1−x−yGexCy is found to be inferior to that of Si1−xGex with similar Si/Ge concentration ratio, grown under identical conditions, and the quality deteriorates with increasing C fraction. Also, the surface roughness, as studied by tapping mode atomic force microscopy, increases with increasing C fraction as well as with increasing Ge fraction, suggesting a transition from Frank–van der Merwe to Stranski–Krastanov type growth. We suggest that the very large mismatch between the average bond length in the Si1−x−yGexCy material, as determined by Vegard’s law, and the equilibrium Si–C bond length, weakens the Si–C bonds and reduces the elastic range of the material, thus lowering the barrier for dislocation and stacking fault formation. The change in elasticity may also be responsible for the change in growth morphology, either directly by a lowered barrier for island formation or indirectly through the formation of defects. A decrease in Ge incorporation in the Si1−x−yGexCy films with increasing C incorporation suggests a repulsive Ge–C interaction. Moreover, we observe a C-rich, Ge-deficient precursor phase to SiC precipitates at a growth temperature of 560 °C, whereas at 450 °C no such phase can be observed. The temperature dependence of the precursor formation is consistent with C bulk diffusion. Infrared absorption measurements cannot be used to detect the precursor phase. Finally, the onset of epitaxial breakdown is discussed and an accurate and independent determination of the C fraction and its substitutionality is emphasized.
Trapping centres in Cl-doped GaSe single crystals
Authors: Micocci G. , Serra A. , Tepore A.
Published: July 2002

Thermally stimulated current (TSC) and photoconductivity were studied as a function of temperature and light intensity in an n-GaSe single crystal doped with chlorine. TSC measurements were performed in the range 80–450 K, and the results were analyzed by different methods. An electron trapping centre at about 0.38 eV below the conduction band and an electron capture cross section of (8±2)×10−18 cm2 were determined. In this centre retrapping is negligible. A strong thermal quenching of photocurrent was observed at various excitation levels. The photocurrent results were analyzed by a simple kinetic model taking into account two different types of centres. In this way a hole centre about 0.20 eV above the valence band was observed.
Resonant tunneling in a quantum nanosystem with an attractive impurity
Authors: Joe Yong S. , Cosby Ronald M.
Published: July 2002

We present the study of the conductance of a quantum nanosystem containing a finite-size attractive impurity. A single finite-size attractive impurity introduces multiple quasi-bound states in the channel for a sufficiently strong attractive potential, and these states give rise to multiple resonant peaks before the first plateau in the conductance. These resonant peaks, arising from the resonant tunneling through the multiple quasi-bound levels, have a Lorentzian shape centered around the resonant energy and exhibit a dramatic variation in the linewidths with resonant energy. The strength of the attractive impurity in the constriction is shown to strongly affect the resonant energy and the mean lifetime of each tunneling peak. The temperature dependence of the resonant peaks of conductance is also discussed.
Micro-Raman study of diamondlike atomic-scale composite films modified by continuous wave laser annealing
Authors: Wan J. Z. , Pollak Fred H. , Dorfman Benjamin F.
Published: July 2002

We have modified the properties of diamondlike atomic-scale composite (DLASC) material of various thicknesses (5–70 μm) by means of cw Ar-ion laser annealing using a focused beam (∼2 μm spot size). These DLASC films [amorphous “diamondlike/quartzlike” a-(C:H/Si:O)] constitute a novel class of diamond-related materials. The laser annealing effects were investigated by micro-Raman scattering. The structure of these films can be altered locally from amorphous to nanocrystalline depending not only on the parameters of the annealing process (annealing time, laser intensity) but also the mechanical properties (hardness, stress) of the films. For comparison purposes we also measured the effects of thermal annealing.
Fabrication of lateral npn- and pnp-structures on Si/SiGe by focused laser beam writing and their application as photodetectors
Authors: Engel C. , Baumgartner P. , Holzmann M. , Nützel J. F. , Abstreiter G.
Published: July 2002

Local doping with focused laser beam writing was used to fabricate lateral npn- and pnp-structures on modulation-doped Si/SiGe heterostructures. The electrical and optical properties of the achieved lateral potential modulation were analyzed for local B-doping on n-type Si/SiGe and P- and Sb-doping on p-type SiGe/Si. Focused laser beam written doped lines show a strongly nonohmic IV characteristic indicating the formation of a local insulating barrier in the two-dimensional carrier system. Such lateral structures can be used as photosensitive devices with responsivities up to 106 A/W combined with a spatial resolution on the μm scale.
Method for triggering high voltage vacuum discharges
Authors: Händel S. K. , Nordhage F. R.
Published: July 2002

By application of a specially designed trigger electrode on which a laser beam is focused, it is possible to obtain a reliable method for initiation of high voltage vacuum discharges. The trigger electrode plasma generated by the laser beam has been studied with regard to its light emission. The result proved that the light intensity reaches its peak value about 200 ns after application of the laser trigger pulse. In addition, by using the triggering method presented, investigation of the high voltage vacuum discharge characteristics—current derivative (dI/dt), current, and x-ray output versus time—has been carried out. Recorded traces indicate pinching of the inter-electrode discharge channel but also x-ray emission during this event.
Comparison between giant magnetoresistance in Fe–Co–Ni/Cu multilayers and anisotropic magnetoresistance in the ternary alloys
Authors: Miyazaki T. , Kondo J. , Kubota H. , Inoue J.
Published: July 2002

The concentration dependence of giant magnetoresistance (GMR) at the second peak in the Fe–Co–Ni/Cu multilayers and that of anisotropic magnetoresistance in the Fe–Co–Ni ternary alloy films and ribbons in the fcc γ-phase structure have been systematically examined at 4.2 K and room temperature. The concentration dependence of the GMR ratio is well explained by taking into account the spin-dependent interface and bulk scattering and the spin-independent scattering.
Magnetic anisotropy in giant magnetoresistive CoAg granular films (abstract)
Authors: Gester M. , Henry Y. , Thompson S. M. , Gregg J. F. , Ounadjela K.
Published: July 2002

A correlation is found between the room temperature giant magnetoresistive (GMR) behavior and the direction of the easy axis of the magnetization in molecular beam epitaxy grown CoAg granular films. Samples containing between 15 and 50 at. % Co were prepared by co-evaporation at temperatures ranging from 0 to 600 °C. GMR curves are recorded with the current in the film plane and the external field either parallel or perpendicular to the film. Out-of-plane torque magnetometry has been used to determine the anisotropy energies and carry out a full directional analysis. Below Co concentrations of 30 at. %, the GMR curve for the field perpendicular to the plane always decreases more rapidly than for the field parallel to the plane. In contrast, for higher Co concentrations, the in-plane GMR decreases more rapidly at low fields and then crosses over the out-of-plane GMR curve. Thus, the maximum GMR is always observed when the field is perpendicular to the plane. Torque measurements show that for all growth temperatures, the direction of the easy axis of magnetization changes from out-of-plane to in-plane with increasing Co concentration. This crossover shifts to lower Co concentrations as the growth temperature increases. The maximum anisotropy energy density is larger in the case where the easy axis lies in the film plane. Unexpectedly, for all growth temperatures two uniaxial anisotropy contributions are found to coexist in films containing 20 at. % of Co. We attribute our findings to the shape anisotropy of the magnetic grains, which is dominated by columnar growth at low and thin film like behavior at high Co concentrations, respectively.
Phase segregation and giant magnetoresistance behavior in as-deposited Co-Ag film grown by pulsed laser deposition
Authors: Zhang Wei , Boyd Ian W. , Cohen Neil S. , Bui Quang T. , Pankhurst Quentin A. , Elliott Martin , Herrenden-Harkerand William
Published: July 2002

The growth of Co-Ag granular films on Si (100) substrates by pulsed laser deposition (PLD) is reported. It is found that phase segregation can be directly produced in as-deposited Co-Ag granular films. This is attributed to the high quench rates induced by PLD, unlike the film deposited by sputtering, where post-annealing is required to achieve the required phase segregation. A large magnetoresistance (MR) value of around 27% was obtained at 4.2 K under a magnetic field of 4.7 T in as-deposited Ag0.70Co0.30 films. Our results suggest that the large magnetoresistance values obtained are strongly determined by phase segregation and particle size in association with the laser fluences used.
Implementation of vector moving Preisach model using texture coefficients as easy axis distribution
Authors: Seol S. C. , Kang T. , Shin K. H. , Lee T. D. , Park G. S.
Published: July 2002

Vector moving Preisach model was applied to the untextured Co thin film media. The out-of-plane easy axis distribution of the particles was derived directly from the texture coefficient phkl obtained from x-ray diffraction analysis, which corresponds to the fraction of the grains that have {hkl} plane lying parallel to in-plane direction. In order to validate this variable, angular dependence of magnetic properties of CoCrPPt/Cr/glass thin films with two different composition was measured by using a vibrating-sample magnetometer. Simulated results showed little difference from the measured data.
Experimental validation of the Preisach accommodation properties of recording media
Authors: Vajda Ferenc , Bennett Lawrence H. , Swartzendruber Lydon J. , Rugkwamsook Pattana , Torre Edward Della
Published: July 2002

The characterization of accommodation plays an important role in determining both the archival and the recording properties of magnetic recording materials. In this article the basic properties of the recently proposed accommodation paper were experimentally investigated on a commercial flexible disk material. The new technique of operative field accommodation was used in our measurements. It was seen that the direction of the drift in remanence depends on the initial field reversal and that the amount of accommodation depends not only on the width of the minor loop, but the extrema values, as well. Although the amount of accommodation depends on the field reversal points, it was seen that for any initial field reversal point, when cycling between the same operative field values, the stable minor loop is always the same. It was found that if |h1|=|h2|, that is, the accommodation process is symmetrical in the operative field, the stable minor loop is also symmetrical. The amount of accommodation was found to be maximized for a process in which |h1|=|h2|=hi. The latter property could be utilized to accurately measure the accommodation parameter, β.
Ferromagnetic resonance and x-ray diffraction investigations of ion irradiated Ag/Fe/Ag-(001)-films
Authors: Kurowski D. , Meckenstock R. , Pelzl J. , Brand K. , Sonntag P. , Grünberg P.
Published: July 2002

High fluence implantation of 95-keV Fe-ion in epitaxial Ag/Fe 200 Å/Ag-(001)-multilayers were performed to induce structural modifications. The correlation between structural quality and magnetic properties was investigated by measurements with ferromagnetic resonance (FMR) and out-of-plane x-ray-diffraction techniques (XRD). The FMR results show for fluences up to 1015 cm−2 a decrease of the crystalline- and perpendicular-uniaxial anisotropies, which are attributed to strain relaxation due to the ion-irradiation detected with XRD. From these results the magnetoelastic coefficient B1 is determined to −3×106 J/m3. At higher fluences of 1016 cm−2 we observe a strong reduction of the perpendicular-uniaxial anisotropy and a change of the crystalline anisotropy from cubic towards that of a tetragonal symmetry. Further, increasing fluences lead to a lattice widening above the Fe-bulk value and an increase of the interface roughness.
Theoretical predictions of magnetic interface anisotropy in Co/Pt superlattices (abstract)
Authors: Ortiz-Sitza S. , MacLaren J. M.
Published: July 2002

Superlattices with both large perpendicular magnetocrystalline anisotropy and Kerr rotations in the range of visible light are potential materials for high-density magneto-optic recording media. Transition metal superlattices formed from Co and Pt have been the focus of recent interest since they have both of these desirable properties. In this study, the intrinsic magnetocrystalline anisotropy of several Co/Pt superlattices is computed from ab initio local spin-density electronic structure calculations. In the case of nCo/5Pt [111], extrapolating the anisotropy to zero Co thickness yields an interface anisotropy of 0.90 ergs/cm2 in good agreement with previous estimates of 0.85 ergs/cm2 based upon the Neèl model.1 Results for the anisotropy versus Co thickness will be presented for several different growth directions and the results compared to experiment and analyzed in terms of the Neèl model.
Investigation of anisotropy effects on interlayer exchange coupling by locally resolved photothermally modulated ferromagnetic resonance
Authors: Meckenstock R. , Pelzl J.
Published: July 2002

In this work we explore the temperature dependence of the interlayer exchange coupling in correlation with the behavior of the different anisotropy contributions using a laterally resolving ferromagnetic resonance (FMR) technique the photothermally modulated (PM)–FMR. The system investigated for this purpose was a Ag/Fe/Ag-wedge/Fe/Ag-system grown by molecular beam epitaxy. The lateral resolution achieved in the PM–FMR experiment was 20 μm. For the first time the lateral resolved PM–FMR experiments were performed at different temperatures in the range of 150 K–360 K, the temperature dependence of the magnetic anisotropy parameters and the interlayer exchange of the Fe/Ag system could be measured with a minimum set of samples with a very high accuracy. The correlation between the temperature dependence of the crystalline and the surface anisotropy yields the experimental evidence, that both anisotropies stem from the same microscopic mechanism.
New mode of domain imaging: Second harmonic generation microscopy (abstract)
Authors: Kirilyuk V. , Kirilyuk A. , Rasing Th.
Published: July 2002

Magnetization induced second harmonic generation (MSHG) is a novel magneto-optical technique that has an enhanced surface/interface sensitivity and demonstrates very large magneto-optical effects.1 It is described by a generalized nonlinear optical tensor χ(2) which has different transformation properties as compared to the linear tensor χ(1). As a consequence, in the same geometry MSHG may be sensitive to other magnetization components than linear magneto-optics. Therefore linear and nonlinear magneto-optics should work best in a combination. Here we report the development of a magneto-optical microscope that is sensitive simultaneously to the linear (Faraday or Kerr) and nonlinear (MSHG) magneto-optical effects. MSHG, on the one hand, is able to visualize some exotic domain structures, e.g., 180° domains in antiferromagnetics and ferroelectrics. On the other hand, because of its interface sensitivity it might help to visualize the magnetic structure at the interface between two different magnetic materials (including metals). Last but not least, the microscope evidently has an enhanced resolution due to the frequency doubling of detected light. First, we apply the microscope to the study of domains in magnetic garnet films, where a considerable difference between Faraday and MSHG images in the same configuration is demonstrated. A complicated noncollinear domain structure is straightforwardly derived from the MSHG images. Next, we consider the application of our technique to the magnetic metal surfaces and thin films (in reflection). The utilization of the microscope to correlate the surface/interface morphology with its magnetic properties is discussed.
Parametric amplification of solitons in magnetic films (abstract)
Authors: Bagada A. V. , Melkov G. A. , Serga A. A. , Slavin A. N.
Published: July 2002

Envelope solitons propagating in a weakly dissipative medium broaden, and their amplitudes decrease twice as fast as the amplitude of a sinusoidal signal. In optics, these effects are compensated by erbium-doped fiber amplifiers inserted in a communication line.1 In our present paper, we report the observation of a parametric amplification of spin wave envelope solitons propagating in yttrium–iron–garnet (YIG) films. We used a conventional delay-line structure2 consisting of an input and output transducers (width 50 μm) separated by l=8 mm, and a third transducer placed in the middle. A tangentially magnetized (He=910 Oe) YIG film (thickness 6.4 μm, 2ΔH=0.5 Oe) was placed in the delay-line structure. Rectangular pulses of backward volume magnetostatic waves (duration T=30–40 ns, carrier frequency f=4.65 GHz) were launched at the input transducer. Parameters of the input pulses were chosen to guarantee a single-soliton regime of pulse propagation.2 To create an active region under the middle transducer, a microwave pumping of the frequency 2f=9.3 GHz and power 0.3–10 W was supplied to that transducer τ μs earlier than the input pulse was launched. We measured the gain coefficient for the propagating soliton (defined as the ratio of peak powers of the output pulses with and without pumping) as a function of the pumping power. The results are presented in Fig. 1 for τ=0.25 μs and τ=3.00 μs. When the time interval τ was smaller than the characteristic time of development of parametric instability of pumping field τp=2π/γΔH=1.43 μs, the propagating soliton was amplified (G>0). When τ>τp, the propagating soliton was attenuated (G<0) due to its interaction with parametric waves of the frequency f resulting from the parametric decay of the pumping field. We believe that by using a dielectric resonator instead of the middle transducer we will get considerably higher values of gain G for spin wave solitons in YIG films.
Magnetic ordering and magnetic excitations in the induced moment distorted triangular antiferromagnet TlFeCl3 under hydrostatic pressure (abstract)
Authors: Monteith A. R. , Petitgrand D. , Visser D.
Published: July 2002

The magnetic ordering and magnetic excitations in the induced ferromagnetic chain compound TlFeCl3 have been studied by means of elastic and inelastic neutron scattering under a hydrostatic pressure of 5 kbar. A partial commensurate magnetic ordering has been observed at TN1=5.81 K. A second transition to a fully ordered 120° triangular structure takes place at TN2=4.2 K. The critical exponent of the magnetic sublattice magnetization β=0.29 (1) was established. The magnetic excitations were determined along the chain direction as well as the [110] direction. The single ion anisotropy and superexchange parameters at 5.0 kbar, T=2 K were also obtained.
Basal plane magnetoelastic stress in magnetic Dy/Y and Er/Lu superlattices
Authors: del Moral A. , Ciria M. , Arnaudas J. I. , Ward R. C. C. , Wells M. R.
Published: July 2002

The basal plane (bp) cylindrical symmetry breaking magnetoelastic stress (MS), Mγ, has been measured for the series of superlattices (SL) (Dyn/Y15) and (Erm/Lu10), with n=5, 15, 25, and m=10, 20, 30 atomic bp, from 10 K and in applied magnetic fields up to B=12 T, using a capacitive cantilever technique. Field induced transitions are observed. For both series of SLs an effective strong interfacial MS is determined at 10 K and 12 T, up to about one order of magnitude larger and of the opposite sign than the bulk MS. Mγ (12 T) scales with the power m3 of the reduced magnetization m confirming its crystal electric field origin.
Magnetotransport in doped manganate perovskites (invited) (abstract)
Authors: Sun J. Z. , Krusin-Elbaum L. , Gupta A. , Xiao Gang , Duncombe P. R. , Gallagher W. J. , Parkin S. S. P.
Published: July 2002

Recent progress in oxide perovskite thin-film technology has led to the discovery of a large negative magnetoresistance at room temperature in the doped manganate perovskite thin films. For applications such as magnetic-field sensing, the saturation magnetic field for large magnetoresistance has to be significantly lowered. The magnetic and transport properties of the doped manganates involve a curious magnetic-field scale, on the order of 1–10 T. Upon the application of a field on this scale, the magnetoresistance saturates, and a significant broadening of the temperature-dependent magnetization is seen. An understanding of the materials physics that underlie such behavior can point to new ways of lowering the saturation field in this class of materials. We argue that this characteristic field is suggestive of an inhomogeneous magnetic state in the system. We will discuss the basic phenomena and physics of magnetotransport in this class of materials. We will also report the successful fabrication of a trilayer thin-film pillar structure made using the doped manganate perovskites in which a magnetoresistance change by about a factor of 2 was observed at temperatures below 100 K in a field less than 200 Oe, proving that large magnetoresistance in low field can be obtained in these materials.
Spin dependent transport perpendicular to CoPt/S/Co (S=Si, Ge) trilayer
Authors: Matsuyama K. , Asada H. , Saeki T. , Sawamoto Y. , Taniguchi K.
Published: July 2002

In this article, we report spin dependent electron transport perpendicular to a ferromagnet/semiconductor/ferromagnet trilayer with the current perpendicular to the plane (CPP) geometry and fabricated by a photolithographic technique. The CPP current was defined with a contact hole of 20 μm diameter produced in a SiO2 spacing layer. A CoPt/S/Co trilayer was used in the present study. Various film deposition methods were studied for optimum performance. A superior hard magnetic property was obtained in rf sputtered CoPt, which results in a well defined selective magnetization switching between CoPt and Co layers. The magnetoresistance (MR) effects have been confirmed by the measurement of MR hysteresis for various semiconductor layers. The values of MR change ΔR at room temperature observed in sputtered Ge (42 nm), evaporated Si (30 nm), and sputtered Si (16 nm) were 0.40 mΩ (R=1.3 Ω), 0.30 mΩ (R=2.4 Ω), and 5.5 mΩ (R=19 Ω), respectively. The magnetron sputtering was found to be a most promising method for producing a pinhole free semiconductor layer of order 20 nm thickness.
Exchange interactions in (FeT)90Zr10(T=Ru,Mn) metallic glasses (abstract)
Authors: Paulose P. L. , Bhattacharya S. , Nagarajan V.
Published: July 2002

Recently there have been several theoretical reports about models of amorphous transition metal alloys which take into account the fluctuations of local magnetic moments due to structural disorder.12 It is predicted that the local atomic moment on an atom depends on the number of first near neighbors with short distances (contracted atoms) and it could be positive, negative, or negligible. An amorphous Fe–Zr system could be a typical system to study these features which have a key role in determining the magnetic structure. Fe90Zr10 orders ferromagnetically at 230 K and exhibits a mixed state at T<30 K showing spin glasslike behavior. Here we present the results on Mn and Ru substitution for Fe in Fe90Zr10. Mn is known to couple antiferromagnetically (AF) to Fe while Ru is expected to be nonmagnetic. We find that Mn reduces the Curie temperature (Tc) gradually while the spin freezing temperature (Tf) remains nearly constant. However, in the case of Ru, Tf drastically increases and 5 at. % Ru drives the system to a clear spin glass state. Hyperfine field studies show gradual evolution of AF coupled spins and their distribution, pointing out the existence of a well defined bimodal distribution. Fe–Fe exchange is believed to become antiferromagnetic for Fe–Fe distances <0.15 nm and the possible occurrence of short Fe–Fe distances in an amorphous matrix is often cited as the reason for the competing interactions to occur. However, Ru with a larger atomic size should have resulted in long Fe–Fe distance (which we have found in crystalline Fe2Zr which is a closed packed structure3). We propose that the dilution of Fe moment and the band modifications due to Ru substitution seemed to promote antiferromagnetic coupling in a Fe–Zr system.
Polarized neutron diffraction studies of antiferromagnetic EuTe/PbTe superlattices (abstract)
Authors: Kepa H. , Giebultowicz T. M. , Goldman K. I. , Nunez V. , Majkrzak C. F. , Springholz G. , Bauer G.
Published: July 2002

PbTe is a nonmagnetic semiconductor, and EuTe, also a semiconductor, is a type II fcc antiferromagnet below TN=10 K. Our earlier diffraction studies of [(EuTe)m|PbTe)3m]N samples (with m=2–7, N=200–600) showed that the type II ordering is preserved in the EuTe layers,1 but the lattice strain always selects an arrangement with the (111) ferromagnetic (FM) sheets (characteristic for the type II structure) parallel to the layers. In addition, samples with n⩽5 scans through the antiferromagnetic (AFM) maxima reveal pronounced patterns of satellite peaks—a clear signature of interlayer spin coherence, indicating that Eu–Eu interactions are transferred through PbTe barriers even as thick as 55 Å! The origin of this surprisingly long-range interaction cannot be understood on the grounds of the existing theories of interlayer coupling, in which high concentrations of conduction electrons always play a crucial role,2 because EuTe is insulating at low T and in PbTe n is as low as ∼1017 cm−3. In order to identify the coupling mechanism, we have begun new studies using polarized neutron diffraction. This technique is particularly useful for investigating the AFM domain arrangement. While the (111) symmetry allows six nonequivalent type II configurations, gradually increasing field should align all spins perpendicular to H, interfering with the coupling forces. Eventually, it should destroy the interlayer coherence—“monitoring” of this process may therefore reveal the much needed information about the interlayer coupling strength. Our experiments show a drastic differences in the system behavior depending on the “cooling history.” If the sample is cooled at H=0, then a modest field (∼0.5 T) indeed leads to the expected domain rotation. Further H increase induces a growing ferromagnetic component, and gradually suppresses the AFM one—however, the interlayer coherence in the AFM ordering can be still seen up to surprisingly high H values ∼5 T). On the other hand, if the sample is cooled through TN with the field on, then H as weak as 0.02 T already destroys the interlayer correlations. Explanation of the observed facts and estimates of the interaction strength based on model calculations will be presented, and some possible physical mechanisms undering the interlayer coherence (e.g., coupling by dipolar forces or coupling involving bound carrier states) will be discussed.
Disclinations, crystal fields, and easy axes of magnetization in the hard magnets (abstract)
Authors: Watson R. E. , Melamud M. , Bennett L. H.
Published: July 2002

There is a need for increased insight into the origins of the easy axes of magnetization of the transition metal-rare earth hard magnets. These systems form in Frank Kasper or closely related crystalline structures. David Nelson has pointed out1 that these topologically close packed phases are threaded with disclination lines. The principal chains among these lines, as they pass through rare-earth sites, appear to define the orientations of the crystal fields at these sites and, in turn, the low-temperature easy axes of magnetization. The currently available experimental data are shown to be in almost perfect accord with this definition of easy axes. Using these ideas, predictions are made for systems and structures for which magnetization anisotropy data have yet to be obtained.
Magnetostriction of the itinerant uniaxial ferromagnet Y2Fe14B
Authors: Abadı́a C. , del Moral A. , Algarabel P. A. , Kulakowski K.
Published: July 2002

Magnetostriction measurements have been performed on a tetragonal Y2Fe14B single crystal along all the major symmetry directions at temperatures ranging from 10 to 400 K and applied magnetic fields up to 14 T. The standard irreducible magnetostrictive modes for tetragonal symmetry, εα,1(c), εα,2(c), εα,1(a), εα,2(a), ε1γ(a), and εε(d), have been obtained from the measurements. Their thermal and applied magnetic-field dependence are discussed. The isotropic volume striction modes have been observed to be one order of magnitude higher than the anisotropic ones.
High harmonic generation and turbulence of magnetoelastic excitations in hematite single crystal
Authors: Preobrazhensky V. , Pernod P.
Published: July 2002

Strongly nonlinear resonance of the longitudinal magnetoelastic wave in a hematite single crystal has been studied experimentally. Generation of more than 40 acoustic harmonics by means of a sinusoidal rf magnetic field has been observed in periodic oscillations. Two typical kinds of bifurcations evoked by the variation of external parameters (bias magnetic-field strength, rf field frequency, and amplitude) have been found. The first one corresponds to a slow automodulation of the periodic ultrasonic excitation. The second one is accompanied by fast chaotic oscillations in the temporal domain and by generation of a few incommensurate frequencies in the ultrasonic spectrum similarly to quasiperiodic scenarios of turbulence.
Nonlinear magnetization processes in twinned Terfenol-D crystals (abstract)
Authors: Holden A. P. , Kennedy J. , Halliday N. , Lord D. G. , Jenner A. G.
Published: July 2002

The magnetostriction of the giant magnetostrictive cubic compound Terfenol-D (Tb0.3Dy0.7Fe1.9) changes discontinuously with applied magnetic field.1 Models of the magnetization processes in this material has shown that the sharp changes in magnetostriction arise from nonlinear domain magnetization reorientations.2 Measurements of the transverse magnetization in twinned crystals of Terfenol-D as a function of applied field and crystal orientation are presented from which magnetic domain populations involved in the magnetization processes are deduced. Barkhausen noise spectra provides information complementary to that obtained through magnetization measurements and as such is used to elucidate the discontinuous nature of the domain processes that lead to the sharp changes in magnetostriction in this material. The transverse ac susceptibility measurements have been obtained from bar-shaped specimens, with principle axis parallel to the growth axis 〈112〉 and have been augmented with rotating sample and torque magnetometry on {011} and {112} plane disk samples, from which Barkhausen spectra has been obtained in conjunction with anisotropy measurements. The data indicate that domain wall motion is operative even in fields approaching saturation and that intrinsic stress and wall pinning mechanisms have a significant effect on the achievable magnetoelastic strain. The critical fields associated with domain population changes have been theoretically deduced and are in excellent agreement with susceptibility and Barkhausen data.
Variation of magnetism and structure on mechanically alloyed Fe40Co10Cu50 powder with process time and heat treatment
Authors: Yu Seong-Cho , Yoo Yong-Goo , Kim Won-Tae , Anderson C. , Dickson D. , Zeiske T.
Published: July 2002

The effects of milling time and heat treatment on local structural changes during mechanical alloying Fe40Co10Cu50 have been investigated by means of x-ray diffraction (XRD), neutron diffraction technique, vibrating sample magnetometer, and Mössbauer spectroscopy. Mössbauer spectroscopy showed that two kinds of magnetic phases coexist in the mechanically alloyed powder, which is in agreement with XRD and neutron diffraction study. One is corresponding to α-Fe and the other is a new magnetic phase formed during mechanical alloying. With increasing processing time, the new magnetic phase becomes more ordered and dominant. Mössbauer spectrum from the annealed sample consists of ferromagnetic component with a hyperfine field of 36.2 T and a paramagnetic component.
An x-ray absorption spectral study of the Ce2Fe17−xMx solid solutions, where M is aluminum or silicon (abstract)
Authors: Vandormael D. , Grandjean F. , Briois V. , Middleton D. P. , Buschow K. H. J. , Long G. J.
Published: July 2002

X-ray absorption measurements have been performed at room temperature on the Ce2Fe17−xAlx solid solutions, with x=0 to 9, and the Ce2Fe17−xSix solid solutions, with x=0 to 3. The iron K-edge extended x-ray-absorption fine structure results are consistent with the expected changes in the unit cell volume with increasing aluminum and silicon content.12 X-ray absorption near-edge structure results at the cerium LIII edge reveal a change in the valence state of cerium from a mixture of trivalent and tetravalent in Ce2Fe17 to predominantly trivalent in Ce2Fe17−xAlx and Ce2Fe17−xSix as the aluminum and silicon content increases. This change in valence state corresponds to an increasing partial transfer of electron density from the conduction band to the 4f orbital of cerium, a transfer which is in agreement with the increase in the resistivity observed with increasing aluminum and silicon content.3 The gradual cerium valence change indicates that both aluminum and silicon are, at least in part, covalently bonded to cerium. The increase in bond covalency agrees well with both the preference12 of the aluminum and silicon for the 18h site in Ce2Fe17, the site with the maximum number of three rare-earth near neighbors, and the temperature dependence of the Mössbauer spectral isomer shifts in these solid solutions.4
Magnetic and magneto-optical investigation of CoCrTa and CoCrPt films
Authors: Mapps D. J. , Chandrasekhar R. , Dieu L.
Published: July 2002

Magnetic and magneto-optic measurements (polar Kerr rotation and ellipticity) have been taken for a series of CoCrTa and CoCrPt single layer films with different thicknesses. The magnetic layers were rf sputter deposited onto constant thickness titanium layers on glass substrates at room temperature. Experimental data were obtained at two different wavelengths, i.e., 825 and 670 nm. The perpendicular coercivity Hc measured at the two wavelengths increased with film thickness. Conversely, the lower thickness showed the highest θk and this decreased as the thickness increases. The opposite trend has been noticed for CoCrPt films. There is no difference in the grain size from transmission electron microscopy examination. The results of the investigation are presented in the context of the need for magneto-optic material to be optimized for short wavelength applications in the future.
Magneto-optical properties in Pt1−xNix/Co multilayers
Authors: Zheng M. , Shang C. H. , Wang Y. J. , Chen L. Y. , Shan Z. S.
Published: July 2002

The effects of doping Ni into the Pt spacer layer on the polar Kerr rotation θk and perpendicular anisotropy Ku of the sputtered Pt/Co multilayers have been investigated. A similar tendency of the variations of Ku and θk with the doping concentration of Ni specifies that they arise from the same source, the spin-orbit coupling. An enhanced magneto-optical effect appears in Pt1−xNix/Co multilayers at x=0.08 and can be attributed to variation of the off-diagonal elements of the conductivity tensor.
Optical and magneto-optical properties of MnPt3 films (abstract)
Authors: Wierman K. W. , Hilfiker J. N. , Sabiryanov R. F. , Jaswal S. S. , Kirby R. D. , Woollam J. A.
Published: July 2002

Optically thick films of MnPt3 were prepared by magnetron sputtering onto quartz substrates. Postdeposition annealing at 850 °C resulted in highly textured (111) films with the L12 (Cu3Au) structure. MnPt3 films are ferromagnetic with a Curie temperature of 380 °C, and they show large magneto-optical effects in the visible.12 These films also show a high degree of long-range order. The diagonal components of the dielectric tensor were determined using variable angle spectroscopic ellipsometry measurements over the spectral range 1.2–2.4 eV. Magneto-optic Kerr rotation and ellipticity measurements were made at near normal incidence over the spectral range 1.4–3.6 eV to determine the off-diagonal components of the MnPt3 dielectric tensor. First-principles electronic structure calculations were carried out for the ordered MnPt3 structure, and from these the components of the dielectric tensor were calculated. We find excellent agreement between the measured and calculated diagonal components, but only fair agreement for the off-diagonal components.
Electrodeposition of ultrathin magnetic films of Fe and Co
Authors: Schindler W. , Schneider O. , Kirschner J.
Published: July 2002

We electrodeposited ultrathin magnetic Fe and Co films on Cu(001) crystals from an aqueous 0.3 M Na2SO4/(Fe or Co)SO4 electrolyte in a newly developed electrochemical cell. A deposition procedure of Fe from an organic electrolyte of propylene carbonate has been additionally developed to prevent the significant H2 evolution during the Fe deposition from an aqueous electrolyte. Fe films of more than 8 monolayer (ML) thickness show the easy magnetization axis in plane. The saturation magnetization correlates linearly with the film thickness. In the thickness range between 2 and 8 ML, the easy magnetization axis is in the [001] direction. No magnetization is observed in films with thickness of less than 2 ML. Co films show in-plane magnetization with square hysteresis loops and a linear correlation of the saturation magnetization and film thickness above 2 ML. The magnetization vanishes at coverages of less than 1.5 ML as known from molecular beam epitaxy grown films. The coercive field of the Co films varies approximately linearly from 0.9 mT at 2.5 ML to 25 mT at 51 ML film thickness.
Colossal magnetoresistance behavior in LaCaMnO/CeO2/Si (100) multilayers grown by pulsed laser deposition (abstract)
Authors: Zhang Wei , Boyd Ian W. , Elliott Martin , Herrenden-Harkerand William
Published: July 2002

The La–Ca–Mn–O (LCMO) system grown on lattice matched LaAlO3 substrates by pulsed laser deposition (PLD) has attracted much recent attention because of the colossal magnetoresistance exhibited. Interest in these materials is because of their potential application in the magnetic recording industry where one of the challenges is to integrate the chip signal-conditioning circuits together with the sensing elements. We have previously reported the giant magnetoresistance characteristics of La–Ca–Mn–O films grown on Si (100) substrates by PLD. Although magnetoresistance at 50 K under a field of 4.7 T was more than 35% (Δρ/ρ0), no colossal magnetoresistance values were present, clearly due to the imperfections introduced by the lattice mismatch between film and substrate. In this paper we report the transport properties and colossal magnetoresistance behavior in LCMO/CeO2/Si(100) multilayers grown by PLD. The CeO2 is attractive as a buffer layer due to its lattice constant, a, of 5.411 Å, which is close to that of silicon (the misfit factor, being only 0.35%). And by simply rotating the unit cell 45° in the basal plane, the mismatch is less than 0.16% with LCMO along the a–b plane. It is found that the LCMO/CeO2/ Si(100) multilayers also exhibit a well-defined peak of resistivity versus temperature, a similar behavior to a single LCMO layer on a Si substrate. A magnetoresistance value of more than 93% (Δρ/ρ0) was obtained at 77 K under a field of 12 T. The films have been characterized by vibrating sample magnometer, four-point probe and scaning tunneling microscopy, and details of the influence of the multilayer preparation parameter will also be discussed.
Strain effects in thin films of La0.7Sr0.3MnO3 (abstract)
Authors: Lofland S. E. , Bhagat S. M. , Trajanovic Z. , Kwon C. , Ramesh R. , Venkatesan T. , Fork D.
Published: July 2002

Epitaxial thin films of La0.7Sr0.3MnO3 have been grown by pulsed laser deposition1 onto Si substrates that were buffered with Bi4Ti3O12 and yttrium-stabilized zirconia. They appear to have excellent structural properties as seen by x-ray diffraction and Rutherford backscattering. We will report spin wave resonance (SWR) and electron paramagnetic resonance (EPR) experiments at 10 GHz for 280<T<370 K. We observe drastic changes in the spectra consequent upon small variations in temperature: (i) At 295 K, the linewidth of the first spin wave mode is only 15 Oe (the narrowest ever observed in a manganite), and the field positions Hn of the SWR follow the simple n2 dependence expected of a uniform film, n being the mode number.2 (ii) Below 280 K, the SWR spectra developed other structures, and the resonance positoins do not follow any simple model. (iii) When T is raised to about 300 K, Hn assumes a linear dependence on n, suggesting that the film magnetization has developed a parabolic spatial variation. (iv) Near 350 K, the linewidth effectively diverges. (v) At 370 K, an EPR line with a width of only 170 Oe appears. As shown previously,3 a peak in the linewidth near the Curie temperature TC can arise from a distribution of TC values. However, in the present film, the line essentially loses it integrity near TC as if the magnetic network were splitting into several substructures. The recovery in the paramagnetic state, one can imagine, happens because the magnetic phase is liquidlike and, thereby, homogeneous. The present observations dramatically demonstrate that to produce thin films of manganites that have desirable properties over a wide T interval, it is essential to ensure a lattice match that is not upset by T variation.
Skew angle, media orientation and head-disk spacing change in proximity recording systems
Authors: Liu B. , Hu S. B. , Soo K. T. , Low T. S.
Published: July 2002

Experiments reported in this work indicate that for the same head-disk spacing, the outer diameter, corresponding to higher skew angle, is more sensitive to the spacing variation. Conducted investigations cover peak detection channels, PRML channels, oriented media, isotropic media, and the same conclusion can be drawn. Increased skew angle will increase the nonlinear transition shift in the write process. Such phenomena can be observed from both the isotropic media and the media with strong orientation.