RESUMO
The magnetic properties of full Heusler alloy (Co(2/3)Fe(1/3))(3+x)Si(1-x)/GaAs(001) hybrid structures grown by molecular beam epitaxy have been investigated. The magnetic moment, the coercive field and the in-plane magnetic anisotropy of (Co(2/3)Fe(1/3))(3+x)Si(1-x) films with various Si compositions (-0.46≤x≤1) are discussed. The increase in amount of Si results in a significant reduction in the cubic magnetocrystalline anisotropy constant |K(1)(eff)|. K(1)(eff) changes sign and saturates near the stoichiometric composition of Co(2)FeSi and the easy axis of the cubic component changes from the [Formula: see text] direction to the [Formula: see text] direction accordingly. However, due to the presence of a dominating uniaxial magnetic anisotropy component, the easy axis of magnetization in total is shifted to the [110] direction. The saturation magnetization of stoichiometric Co(2)FeSi films turned out to be 1250 ± 120 emu cm(-3), being equivalent to 6.1 ± 0.57 (µ(B)/formula unit (fu)). The relatively close value of magnetic moment to the theoretically expected integer value (6 µ(B)) suggests that Co(2)FeSi films could be half-metallic ferromagnets.
RESUMO
A study of the surface morphology of homoepitaxial GaAs(001) by means of ex situ atomic force microscopy in air reveals the reentrance of mounding behavior at low growth temperatures. A transition from statistical roughening to organized mound formation is observed as the growth temperature is reduced. We show by means of growth simulations that the observed morphology is compatible with anisotropic adatom diffusion in the presence of an Ehrlich-Schwoebel barrier. The mechanism leading to this kind of adatom kinetics at low temperatures is interpreted in terms of surfactant acting arsenic condensing on the surface.
RESUMO
The reversal processes of magnetization in epitaxial MnAs nanotubes prepared by an overgrowth on the sidewall of GaAs nanowires having a diameter of 26 nm are investigated. While the magnetic hard axis is aligned in the direction of the nanowire axis, we apply an external magnetic field perpendicular to the axis to examine the flipping characteristics of magnetic moments. We determine the contributions from the substrate by a direct measurement in order to extract the magnetization of the core-shell heterostructures. The abrupt change in the thus-obtained magnetization due to a flip when the field is varied exhibits an overshoot at about 0.4 kOe for samples with a thickness of the ferromagnetic shell (40-50 nm) larger than the diameter of the core. Moreover, the peak value exceeds the value when the field is swept in the opposite direction. The magnetic hysteresis loop consequently involves line crossings. We speculate that the spin textures of domain walls in such thick hollow cylinders and their movement at the magnetization flip are affected by the geometry and magnetostatic interactions of various origins, giving rise to the anomalous behaviour.
RESUMO
We present a diode-pumped Nd:glass fiber laser, emitting at 1060 nm, that is passively mode locked by fast nonlinear loss in low-temperature-grown GaAs (LT-GaAs). This new mode-locking mechanism is based on intensity-dependent defocusing in LT-GaAs that occurs after nonresonant generation of free carriers by two-photon absorption. Mode locking is self-starting and produces pulses as short as 4.1 ps.