[en] The dynamic hysteresis scaling behavior in epitaxial Fe/GaAs(001) and Fe/InAs(001) thin films (thickness range 7.3 - 150 Aa) has been investigated as a function of Fe film thickness in the field sweep rate range 0.005 - 1000 kOe/s using the magneto-optic Kerr effect. The hysteresis loop area A follows the scaling relation A∝(dH/dt)^α. We find two distinct dynamic regimes: the low dynamic regime in the sweep rate range 0.005 - 250 kOe/s, and the high dynamic regime beyond 250 kOe/s. There is a marked increase in α between the low and high dynamic regimes which we attribute to the dominant reversal mechanism changing from domain wall motion to nucleation. In the low dynamic regime α is a decreasing function of Fe film thickness, and this behavior is attributed to the effect of interface-induced pinning. [copyright] 2001 American Institute of Physics

[en] Two major problems in spin electronics remain to be solved: room temperature spin injection at a source and spin detection at a drain electrode. The lateral size of magnetic contacts and the presence of a potential barrier at the interface are believed to have a key influence on the efficiency of both of these processes. We therefore aimed to clarify these issues by studying spin-polarized transport across epitaxially grown single crystal Fe (001)/GaAs nanoclusters and at the Schottky barrier formed at Ni₈₀Fe₂₀/GaAs interfaces. We observed a negative contribution to the magnetoresistance of an ultrathin (2.5 ML) discontinuous epitaxial Fe film as occurs in tunnel magnetoresistance. This result suggests that spin transport via GaAs is possible on the nanoscale. In the continuous NiFe/GaAs structures, circularly polarized light was used to create a population of spin-polarized electrons in the GaAs substrate and spin-polarized electron transport across the interface at room temperature was detected as an electrical response associated with the field-dependent photocurrent. Surprisingly, highly efficient spin transmission is observed at room temperature, indicating that there is no significant loss of spin polarization for electrons crossing the interface. This result unambiguously demonstrates that spin detection is possible at room temperature in a continuous ferromagnet/semiconductor contact in the presence of the Schottky barrier. [copyright] 2001 American Institute of Physics

[en] We report on the effect of oxygen on the CO-induced 90 degree spin switching in the Co/Cu(110) system [Hope , Phys. Rev. B 57, 7454 (1998)]. The epitaxial fcc Co films were grown on the unsaturated Cu(110)-{2times1}O surface and their magnetic properties have been studied with in situ magneto-optic Kerr effect. The easy axis switch of the Co(110) films is suppressed when Co is grown on O exposed Cu surfaces. Scanning tunneling microscopy images of the film surface reveals the growth of elongated nanostructures preferentially oriented along the [001] direction, providing step-like edges for gas adsorption. The density of steps is similar to the density developing during growth on the clean Cu(110) surface but the step edges now run in the perpendicular direction. The suppression of the easy axis switch can be attributed to subtle changes of the number and adsorption probability of the available atop adsorption sites along the step edges for CO chemisorption. Our experiments highlight the remarkable chemical sensitivity and adsorption site dependence of the easy axis switch of the Co(110) nanomagnets. [copyright] 2001 American Institute of Physics

[en] Real time resolved scanning Kerr microscopy has been used to study the switching dynamics of 50 μm diameter epitaxial Fe(100) disks. The measurements were performed using a sinusoidal sweeping field with a sweep rate of dH/dt=10kOe/s. By performing repetitive one-shot measurements, we have mapped the statistical fluctuations and the probability distribution of characteristic switching parameters as the switching instant t₀, and the switching speed, V. We observe a substantial difference in the parameters estimated from the average of several measurements compared to the parameters extracted from the probability distributions. This illustrates the potential risks of using averaging techniques in dynamic measurements, in addition to the loss of the statistical information. The disks were found to display an inhomogeneous switching, which is believed to be caused by defect damped motion of the domain walls and a inhomogeneous distribution of defects. [copyright] 2001 American Institute of Physics

[en] Reported here is the development and implementation of an integrated in situ magnetoelastic measurement setup with a MOKE magnetometer, repositionable electromagnet, and sample transfer/straining device. The former were used within a molecular beam epitaxial vacuum growth chamber. Consequently the magnetostriction constants for both Cr capped and uncapped Fe/GaAs(100) films were acquired without film oxidization occurring. Samples were bent in a four point bending geometry to produce a quantifiable tensile mechanical strain on the films during magnetoelastic measurements. In addition, a laser measurement system was developed to confirm the induced strain in the samples.

[en] This paper presents the impact of different types of burnable poisons and filling methods on burnup in the VVER-1000 reactor. In this study, SuperMC was used to visually model the fuel assembly of the VVER-1000 reactor, perform burnup calculations and compare the results. Five groups (Homogeneous Gd2O3, Heterogeneous Gd2O3 1and 2, Homogeneous AmO2, Pure UO2) of different burnable poisons are modeled with fuel assembly as a unit, and the results will be analyzed by comparing the difference of keff. (paper)

[en] The fundamental magnetism of the Fe film of 4 ML thick epitaxially grown on GaAs(100) was studied using ex situ ferromagnetic resonance (FMR) at room temperature. In parallel geometry the resonance fields were found to be strikingly different along [0 bar 11] (2170 Oe) and [011] (3360 Oe) direction, exhibiting a large uniaxial anisotropy with the easy and hard directions along [0bar 11] and [011], respectively. For perpendicular geometry the data of FMR show an abnormally low resonance field of 5050 Oe. It implies a pronounced reduction of effective magnetization. This can be explained by a combination of the shape anisotropy of the nanoclusters with their large perpendicular anisotropy. The g factor of these nanoclusters is even smaller than the bulk value. The linewidth is also obviously anisotropic, 220 Oe in easy direction, [0bar 11] and smaller by 50% in hard direction, [011]. [copyright] 2001 American Institute of Physics

[en] The spin and orbital magnetic moments and the perpendicular magnetic anisotropy of 8 and 33 monolayer epitaxial bcc Fe films grown on GaAs(100)-4x6 have been measured using x-ray magnetic circular dichronism and polar magneto-optical Kerr effect. Both the films have approximately the same spin moments of about 2.0μ_B close to that of the bulk value. The ultrathin film shows a giant orbital moment enhancement of about 300% with respect to the bulk value and a perpendicular interface anisotropy field H_s^Fe# - #^GaAs of the order of -5x10⁴Oe. This may be partially due to an increased degree of localization of electronic states at the Fe/GaAs interface associated with the atomic scale interface structure. [copyright] 2001 American Institute of Physics

[en] The boron contribution to the total spin moment in the amorphous alloys Fe_1-xB_x (x=0.2,0.24) has been determined using magnetic Compton scattering. The magnitude of the induced boron moment was found to be ∼-0.04μ_B per formula unit which is a factor of ∼2 less than that suggested by supercell linearized muffin-tin orbital electronic structure calculations

[en] Non-oriented Fe-7.1wt.% Si as-cast strips were produced by twin-roll strip casting process. Then the as-cast strips were hot rolled with different reductions, followed by warm rolling and final annealing. The microstructure, texture evolution and magnetic properties were investigated in detail. The texture of hot rolled sheets with 40% reduction showed strongest {001}<110> texture, whereas the dominated texture was turned into {110}<001> and {110}<112>as the reduction was increased to 56% and 68%. After warm rolling and annealing, the average grain size was decreased firstly and then increased with an increase in hot rolling reduction. In the case of 40% hot rolling reduction, the recrystallization texture was dominated by strong γ (<111>//ND) texture. With an increase in hot rolling reduction, the γ texture was gradually weakened while α (<110>//RD) texture was enhanced. In addition, relatively stronger {100} texture was presented in the sheet of 68% hot rolling reduction. The highest B₅₀ value attained was 1.66 T and the lowest P_10/400 was 24.26 W/kg at a reduction of 56%. (paper)