bluuebunny/crossref_metadata_2025_split huggingface dataset:
Persistent Photo-Hall Phenomenon and Near-Bandedge Absorption in Lightly N-Type Lec GaAs
Authors: Tüzemem S. , Brozel M. R. 
Published: September 2012

ABSTRACTThe novel infrared imaging technique for assessment of undoped semi-insulating (SI) GaAs substrates known as Reverse Contrast is known to result from absorption from point defects whose concentrations approximately anti-correlate with those of EL2, deep donor defects. The absorption that occurs within - 65 meV of Eg in cooled samples is sufficiently strong that commercial wafers can be mapped with simple infrared CCTV imaging equipment. RC defects are thought to be very deep acceptors with an ionization energy close to the Conduction Band. Concentrations of RC defects are not measurable in SI GaAs as they are un-ionized in the dark. Like EL2 defects they can be photo-quenched by irradiation with mid-gap light.In this paper, we present novel Hall Effect measurements on very lightly Te-doped n-type GaAs where at least a fraction of RC defects are ionized. A permanent increase in the carrier concentration is observed after photo-quenching corresponding to the bleaching of RC defects. The carrier concentration returns to its initial value at the same temperature at which the absorption of RC defects is recovered. This result allows a calibration for the absorption coefficient to be found.
Electronic Theory of Gettering and Passivation of Impurities in Semiconductors
Authors: Masuda-Jindo K. 
Published: September 2012

ABSTRACTWe calculate the interaction (segregation) energies Egegr between the extended lattice defects (dislocations and grain boundaries) and impurity atoms in semiconductors by using a microscopic electronic theory. In particular, we use the tight-binding recursion method coupled to the generalized zeros-and poles method and investigate the interaction between the extended lattice defects and various kinds of the impurity atoms in semiconductors (Si). For the systematic understanding of the impurity gettering, we consider a wide variety of impurities, both sp-valence and transition metal impurities, Ti, V, Cr, Mn, Fe, Co, Ni and Cu. We will show that the variation of the gap states plays an important role in determining the interaction energy Esegr between the impurity atom and the extended lattice defects- We also discuss the passivation of the extended lattice defects by interstitial light impurities like hydrogen in Si crystal, we present a simple physical interpretation of the impurity gettering and passivation in semiconductors.
Magnetic and Transport Behavior of Af-Coupled Layers with a Limited Number of Repetitions
Authors: Willekens M.M.H. , Swagten H.J.M. , Duif A.M. , Bloemen P.J.H. , Van Kempen R.J.T. , Lenczowski S.K.J. , De Jonge W.J.M. 
Published: September 2012

ABSTRACTWe investigated the magnetization behavior of [(Co/Pd) 4-Ru]x samples with perpendicular anisotropy and a limited number of repetitions (x = 1,‥,22). In these systems the Co/Pd Multilayers behave as single magnetic entities. A detailed analysis and comparison of the magnetization curves observed by MOKE and VSM permits us to observe the magnetization reversal and hysteresis of the individual layers and to determine the antiferromagnetic coupling J between each pair of layers. A gradual increase in J is observed in all samples when going from the bottom layer to the top layer. Magnetoresistance curves show the same sharp transitions as the magnetization curves. A clear distinction can be made between an outer layer and an inner layer. These results will be compared with model calculations.
Electronic States in Magnetic Quantum Wells
Authors: Ortega J. E. , Himpsel F. J. , Mankey G. J. , Willis R. F. 
Published: September 2012

ABSTRACTWe have searched for the electronic states that mediate oscillatory magnetic coupling in superlattices, and have found strong evidence that these are quantum well states, which are created by quantizing the momentum of s,p-band states perpendicular to the interfaces. The quantum well picture also explains how quantum well states in noble metals become spin-polarized, due to a spin-dependent electron reflectivity at the interface with the ferromagnet. The resulting implications for magnetoresistance are discussed.
Quantum well States in Fe (100) Ultrathin Films Observed by Magneto-Optical Effect
Authors: Suzuki Yoshishige , Katayama Toshikazu 
Published: September 2012

ABSTRACTWe report on the Magneto-optical Kerr rotation (<φ>K) spectra of ultrathin Fe films on Au or Ag (100) substrates and the φK oscillation due to interlayer thickness in Fe/Au/Fe sandwich films. In 3.5–4.5 eV, a new φK peak appears in the bcc-Fe (100) ultrathin films on the fcc-Au (100) surface and it shifts towards the higher energy side with increasing Fe layer thickness. The absolute value of eXy for 3Å (2ML) thick Fe layers is twice as large as that of bulk Fe at 3.7 eV. The thickness dependence of the transition energy of this new peak in the spectra is well explained by the concept of quantum well states in the Fe ultrathin layers, attributing the new transition to a transition from the majority spin Δ5 band ({px±i py), {dxz±i dyZ}; M=±l) to the Δ1 quantum well states (s, pz, dz2; M=0). The new peak is also observed in the Fe/Au (100) artificial superlattices. Using the εxy obtained experimentally for the Fe ultrathin films and the εxy of literature, we can reproduce the experimental φK spectra of the artificial superlattices by optical calculation. On the other hand, we cannot observe the same behavior for the ultrathin Fe films grown on a fcc-Ag (100) surface and covered by a Au (100) ultrathin film, although the εXy of Fe is different from that of the bulk and shows some structures in 2–3 eV. These structures around 2.5 eV are thought to be due to polarized Au atoms adjacent to an Fe layer.An oscillation of φK as a function of interlayer thickness, d, was observed in photon energy region between about 2.5 and 3.8 eV for the Fe (6Å) /Au (dÅ) /Fe (6A) sandwiched film. The oscillation period was about 10Å (5ML) of Au. The oscillation is thought to be closely related with a formation of spin polarized quantum well states of Δ1 band in Au layers sandwiched by magnetic layers.
Quantum-Well Contributions to the RKKY Coupling in Magnetic Multilayers
Authors: Jones B. A. , Hanna C. B. 
Published: September 2012

ABSTRACTWe study the effects of quantum-well states on the calculated RKKY coupling. We find that the bound states of a finite-size potential well of depth V give an added oscillation period of size For the simplest case of a spherical free-electron Fermi surface, thus two periods appear: the original, “fast,” π/kf oscillation, and the quantum-well one The quantum-well contributions have larger amplitude, and are in fact the predominant oscillation. For physically reasonable V (tenths of an eV) this period is around 8–10Å. We discuss evidence for these effects in experimental systems.
Increase in Period of Oscillatory Coupling in Cu by Doping with Ni
Authors: Parkin S.S.P. , Chappertt C , Herman F. 
Published: September 2012

ABSTRACTThe origin of oscillatory interlayer coupling via Cu is explored in sputtered Co/Cu Multilayers by varying the hole concentration in the copper layers by doping with elements of different valence. Detailed studies were carried out for a series of Cu-Ni alloys. The oscillation period of pure Cu is observed to increase monotonically with increasing Ni concentration and is almost doubled for 40 atomic % Ni. The increase in oscillation period can be accounted for by considering changes in the topology of (he Fermi surface of the alloy resulting from the change in band Tilling.
Giant Magnetoresistance in Sputtered NIFE/AG Multilayers
Authors: Rodmacq B. , Mallon A. , Gerard Ph. 
Published: September 2012

ABSTRACTThe Magnetoresistive properties of sputtered Ni8.1Fe1.9/Ag Multilayers have been investigated as a function of both Ag and NiFe layer thicknesses and thermal treatments. For the virgin sample, the Magnetoresistance (MR) ratio at room temperature goes through a maximum of 17% for a Ag thickness of about 11 A. In addition, the R (H) curve is found to be perfectly linear and reversible. Contrary to the MR ratio, the saturation field is observed to decrease continuously as the Ag thickness increases, leading to an increasing slope of the R (H) curves. Upon annealing, we observe both an increase of the MR ratio and a decrease of the saturation field, leading to a three fold increase of the MR slope for annealing temperatures of 280°C. Such a behavior appears to be highly dependent on the layer thicknesses.
Giant Magnetoresistance in Co/Ag Multilayers
Authors: Tan M. , Barnard J. A. , Parker M. R. , Seale D. 
Published: September 2012

ABSTRACTThe Magnetoresistance (MR), Magnetic properties, and crystal structure of dc magnetron sputtered CO/Ag periodic multilayers have been investigated. The Co layer thickness was fixed at -30 Å while the thickness of the Ag layer was systematically varied. ‘Giant’ magnetoresistance was observed. The MR ratio has been found to decline monotonically with increasing Ag thickness in the range 30 Å to 107 Å. Although the maximum room temperature MR ratio is a Modest 4.78%, a more technologically significant measurement of field sensitivity (MR ratio/FWHM of the MR vs. H peak) is a promising 0.1%/Oe at its best. The effect of the number of bilayer units has also been examined and no substantial differences were noted between multilayers containing 8, 9, and 10 bilayer units. Coercivities as determined by both magnetometer and the splitting of the MR peaks are in agreement and increase from 25 to 38 Oe with increasing Ag thickness. Evidence for antiferromagnetic coupling is apparent in the hysteresis loops. High angle X-ray diffractometry (HXRD) in the θ-2θ mode revealed a strong Ag (111) texture in the film, with satellite peaks indicating a layered structure. Low angle XRD (LXRD) also yielded broad superlattice peaks in all samples at least to the second order.
Giant Magnetoresistance in Annealed Fe/Cr Multilayers
Authors: Rensing Noa More , Clemens Bruce M. 
Published: September 2012

ABSTRACTThe giant magnetoresistance effect in antiferromagnetically coupled Fe/Cr Multilayers has been attributed to spin dependent scattering at the interfaces between the constituents. One possible source of this spin dependent scattering is chromium impurities in the iron layers due to intermixing at the interfaces. Annealing the films can promote the diffusion of the components, increasing the impurity concentration and therefore the Magnetoresistance. For this study Fe/Cr Multilayers were annealed at several temperatures and for several durations. Annealing at moderate temperatures (∼ 350°C) increases the Magnetoresistance, while higher temperature anneals (∼ 600°C) cause the magnetoresistance to disappear completely. Long anneals at 330°C (> 100 hours) also reduce the Magnetoresistance. VSM Measurements indicate that the antiferromagnetic coupling is reduced in the annealed samples but show no evidence of Magnetically “dead” alloy layers. Low angle X-ray diffraction indicates that the structural effect of annealing is very subtle in comparison to the significant magnetic effect.
Grain Boundary Diffusion in Co/Cu and Co/Cr Magnetic Thin Films
Authors: Holl-Pellerin John G. , Anderson S.G.H. , Ho P.S. , Coffey K.R. , Howard J.K. , Barmak K. 
Published: September 2012

ABSTRACTX-ray photoelectron spectroscopy (XPS) has been used to investigate grain boundary diffusion of Cu and Cr through 1000 Å thick Co films in the temperature range of 325°C to 400°C. Grain boundary diffusivities were determined by modeling the accumulation of Cu or Cr on Co surfaces as a function of time at fixed annealing temperature. The grain boundary diffusivity of Cu through Co is characterized by a diffusion coefficient, D0gb, of 2 × 104cm2/sec and an activation energy, Ea,gb, of 2.4 eV. Similarly, Cr grain boundary diffusion through Co thin films occurs with a diffusion coefficient, Do,gb, of 6 × 10-2cm2/sec and an activation energy, Ea,gbof 1.8 eV. The Co film microstructure has been investigated before and after annealing by x-ray diffraction and transmission electron Microscopy. Extensive grain growth and texturing of the film occurred during annealing for Co deposited on a Cu underlayer. In contrast, the microstructure of Co deposited on a Cr underlayer remained relatively unchanged upon annealing. Magnetometer Measurements have shown that increased in-plane coercivity Hc, reduced remanence squareness S, and reduced coercive squareness S*result from grain boundary diffusion of Cu and Cr into the Co films.
Quantitative Analysis of Polarized Neutron Specular Reflectivity from a Co/Cu (111) Superlattice at the Second Antiferromagnetic Maximum
Authors: Ankner J.F. , Schreyer A. , Majkrzak C.F. , Bröhl K. , Zeidler Th. , Bödeker P. , Zabel H. 
Published: September 2012

ABSTRACTWe have used polarized neutron reflectivity to prove the existence of oscillatory coupling in MBE-grown Co/Cu (111) superlattices. For a sample of composition [3.4 nm Co/2.0 nm Cu]10, we find that only a small fraction of the sample volume exhibits coherent antiferromagnetic order, with the structure of the remainder of the film being attributable to ferromagnetic domains and small disordered structures.
Observation of X-Ray Absorption Magnetic Circular Dichroism in well-Characterized Iron-Cobalt-Platinum Multilayers
Authors: Jankowski A.F. , Waddill G.D. , Tobin J.G. 
Published: September 2012

ABSTRACTMagnetic circular dichroism in the Fe 2p x-ray absorption is observed in multilayers of (Fe9.5Å/Pt9.5Å)92. The Magnetization and helicity are both in the plane of this multilayer which is prepared by magnetron sputter deposition. This sample is part of a study to examine magnetization in the ternary multilayer system of FeCo/Pt. Lattice and layer pair spacings are measured using x-ray scattering. The atomic concentration profiles of the multilayer films are characterized using Auger electron spectroscopy coupled with depth profiling. Conventional and high resolution transmission electron microscopy are used to examine the thin film, growth morphology and atomic structure.
Magnetic Properties of Epitaxial 6 ML fcc-Fe/Cu (100) Films
Authors: Swartzendruber L. J. , Bennett L. H. , Kief M. T. , Egelhoff W. F. 
Published: September 2012

ABSTRACTA study has been made of the magnetic properties of epitaxial 6 Monolayer (ML) fcc-Fe films on Cu (100) with various thicknesses of epitaxial Cu deposited on top of the Fe. It was found that the magnetic properties undergo striking changes as a function of the Cu thickness. The easy axis of magnetization goes from being in-plane for the bare Fe to perpendicular upon the deposition of 1 ML Cu. Concurrently there is a dramatic decrease in the Kerr signal intensity at saturation. Upon depositing a second ML of Cu the Kerr signal intensity more than doubles, and the easy axis remains perpendicular. For Cu overlayers of 3 ML to 10 ML the Kerr signal intensity at saturation gradually diminishes to below the level of detectability, as if the Fe were nonmagnetic. A superlattice consisting of 60 ML Cu/ (6 ML 57Fe/10 ML Cu)×5/Cu (100) was fabricated and studied at room temperature by conversion electron Mòssbauer spectroscopy. The results confirmed that the Fe is indeed nonmagnetic. The four inner Fe layers of the 6 ML film have the same isomer shift as bulk fcc-Fe in precipitates in Cu, and the two boundary Fe layers exhibit an asymmetric quadrupole doublet.
In Situ Rheed and Magneto-Optic Study of Ultrathin Cobalt Films on (111) Gold Substrate: Effect of a Metallic Overlayer
Authors: S Ould-Mahfoud , R. Megy , N. Bardou , B. Bartenlian , P. Beauvillain , C Chappert , J. Corno , B. Lecuyer , G. Sczigel , P. Veillet , D. Weller 
Published: September 2012

ABSTRACTWe present a comparative in situ RHEED and Polar Magneto-optic Kerr Effect study of the first stages of the growth of a Au overlayer on top of a (111) Co ultrathin film. Drastic behaviours are evidenced on the RHEED diagram, Magnetic anisotropy and coercive force, around 1,5 ML of Au coverage.
Theoretical Studies on the Magnetic Moments of Iron Nitrides Including Fe16N2
Authors: Sakuma Akimasa , Sugita Yutaka 
Published: September 2012

ABSTRACTThe spin-polarized band calculations for the iron nitrides, Fe3N, Fe4N and Fe16N2, have been performed with use of LMTO-ASA Method in the frame of local spin density functional formalism. The results show that the most distant Fe atoms from N have the largest magnetic moment. The central role of the N atom is to bring about the large magnetic moments through the lattice expansion. Concurrently, the N atoms promote an itinerancy of electrons and then in turn prevent the exchange-splitting. This results in an Fe16N2 with the lowest N concentration having the largest magnetic moments. Quantitatively, the obtained magnetic moments are in fair agreements with the experimental results except for Fe16Nr The calculated magnetic moment of Fe6N2 is about 2.4 ΜB/Pε, while the measured value is reported as 3.5 ΜB/FB. The orbital magnetic moment of Fe16N2 is about 0.07 ΜB, which is too small to make up for the difference from the experimental value.
A Tight-Binding Study of Very Thin Transition Metal Film Magnetic Anisotropy
Authors: Pick S. , Dreysse H. 
Published: September 2012

ABSTRACTWe discuss shortly some problems that have been met in recent systematic calculations of the magnetic anisotropy energy (MAE) performed by the present authors as well as in studies of other investigators. As an example, we present MAE for ferromagnetic (001) bilayers with antiferromagnetic inter-plane coupling and for an antiferromagnetic (001) Monolayer. It appears that antiferromagnetism can invoke specific effects and under certain conditions, both MAE and magnetic orbital moment are strongly enhanced.
Magnetization Reversal in CoPt Magnetooptic Recording Alloys
Authors: Kleinefeld T. , Kim W.S. , Valentin J. , Weller D. 
Published: September 2012

ABSTRACTHigh resolution Kerr Microscopy has been used to study newly developed Co25Pt75 alloy films with perpendicular magnetic anisotropy. In particular, the dynamics of magnetization reversal processes wase investigated by means of time resolved domain pattern analysis. Domain wall motion dominated magnetization reversal as well as nucleation dominated processes were observed. Magnetic aftereffect phenomena were confirmed by relaxation measurements of magnetic domains. The fractal dimension of the observed domains is correlated to the macroscopic coercivity determined from hysteresis loop Measurements.
Neutron and X-Ray Scattering Studies of (FeF2) M (CoF2)n Multilayers
Authors: Lederman D. , Belanger D. P. , Wang J. , Han S-J. , Paduani C. , Ramos C. A. , Nicklow R. M. 
Published: September 2012

ABSTRACTWe have performed elastic neutron scattering measurements of the staggered magnetization in (FeF2) M (CoF2) n superlattices. Thermal expansion Measurements, which are proportional to the magnetic contribution to the specific heat, were also carried out using high resolution x-ray diffraction. One of the two measured samples has thicknesses of M = n = 4.5 and the other M = 26 and n = 28 Monolayers, as determined from high angle x-ray θ — 2θ scans. In the M = n = 4.5 sample, only one transition is observed at T/v = 62.9K. Analysis of the neutron data, including the rounding effects, indicates an effective β ≈ 0.42. This does not compare well with the 3D Ising exponent β = 0.325. The X-ray data also show the existence of only one specific heat anomaly at T = 62.8 K. For the M = 26, n = 28 sample, dips in the staggered magnetization and peaks in the thermal expansion were observed at T ≈ 40 K and 74 K. The higher temperature anomaly, associated primarily with the FeF2 layers, is sharper than the lower one, which is presumably rounded by the staggered ordering field imposed by the long range order in the FeF2 regions on the CoF2 regions.
Magnetostriction and Stress in High Moment FeTaN Films
Authors: Cates J. C. , Qiu G. , Haftek E. , Alexander C. , Barnard J. A. 
Published: September 2012

ABSTRACTMagnetostriction and thin film stress have been studied in high moment single layer FeTaN films deposited by high rate reactive dc magnetron sputtering. Low Magnetostriction (Magnitude less than 1 × 10-6) can be obtained over a fairly large range of nitrogen flow rates during film deposition by vacuum annealing at 500°C. After annealing at 500°C for two hours, all films were found to be in a state of tensile stress. Stress versus temperature measurements up to 400°C show film stress in as-deposited films to be highly hysteretic during the first temperature cycle reflecting the films' processing history. Stress-temperature cycles on annealed samples indicate that extremely stable films are produced in an intermediate range of nitrogen content.
Ferrimagnetic Cobalt Ferrite Films Prepared by the Sol-Gel Process
Authors: Wong Eva M. , Zheng Haixing , Mackenzie John D. , Tsuchiya T. 
Published: September 2012

ABSTRACTFerrimagnetic oxide films have been shown to have potential for use as Magneto-optical information storage Materials. Cobalt ferrite films are particularly interesting for magneto optical information storage due to their high magneto optical rotation [1]. In this work, synthesized soluble cobalt (II) and iron (III) Methoxyethoxides were mixed in stoichiometric ratios for use as Co and Fe precursors in the preparation of CoFe2O4ferrimagnetic films. The decomposition of the precursors was characterized by thermogravimetric analysis.CoFe2O4 films were prepared by the dip coating technique using fused silica substrates. These films were then heat treated at temperatures ranging from 200°C to 600°C to study the transformation from an amorphous film to a crystalline film as determined by x-ray diffraction. The Magnetic hysteresis behavior of the films as a function of heat treating temperature and hence crystallinity was also studied. As a general trend, films having a greater degree of crystallinity exhibited larger values of saturation magnetization and remanent Magnetization. The amorphous film was found to exhibit the highest coercive field, but low values of saturation and remanent Magnetization. The effect of heat treating under the influence of a magnetic field of 1.88 kÖe was found to enhance crystallization only slightly and had very little effect on the magnetic properties of the film.
In Situ Analysis of magnetic and Structural Properties of Epitaxial and Polycrystalline Ni80Fe20 Thin Films
Authors: Hashim I. , Atwater H.A. , Watson Thomas J. 
Published: September 2012

ABSTRACTWe have investigated structural and magnetic properties of epitaxial Ni80Fe20 films grown on relaxed epitaxial Cu/Si (001) films. The crystallographic texture of these films was analyzed in situ by reflection high energy electron diffraction (RHEED), and ex situ by x-ray diffraction and cross-sectional transmission electron Microscopy (XTEM). In particular, RHEED intensities were recorded during epitaxial growth, and intensity profiles across Bragg rods were used to calculate the surface lattice constant, and hence, find the critical epitaxial thickness for which Ni80Fe20 grows pseudomorphically on Cu (100). XTEM analysis indicated that the epitaxial films had atomically-abrupt interfaces which was not the case for polycrystalline Cu and Ni80Fe20 film interfaces. The Magnetic properties of these epitaxial films were Measured in situ using Magneto-optic Kerr effect magnetometry and were compared with those of polycrystalline films grown on SiO2/Si. Large Hc (∼ 35 Oe) was observed for epitaxial Ni80Fe20 films less than 3.0 nm thick whereas for increasing thickness, Hc decreased approximately monotonically to a few Oersteds. Correlations were made between magnetic properties of these epitaxial films, the strain in the film and the interface roughness obtained from XTEM analysis.