We systematically measured the dc voltage V(ISH) induced by spin pumping together with the inverse spin Hall effect in ferromagnet-platinum bilayer films. In all our samples, comprising ferromagnetic 3d transition metals, Heusler compounds, ferrite spinel oxides, and magnetic semiconductors, V(ISH) invariably has the same polarity, and scales with the magnetization precession cone angle. These findings, together with the spin mixing conductance derived from the experimental data, quantitatively corroborate the present theoretical understanding of spin pumping in combination with the inverse spin Hall effect.

Raman measurements were performed on molecular beam epitaxially grown GaN before and after implantation with Ar+, Mg+, P+, C+, and Ca+ ions. With increasing ion dose, new Raman peaks arise at 300, 360, 420, and 670 cm−1, independent of the ion species. After rapid thermal annealing at temperatures between 900 and 1150 °C for 15 s, the intensities of the Raman modes decrease with increasing temperature with the exception of the 360 cm−1 mode which shows a maximum in intensity after annealing at 900 °C. The mode at 300 cm−1 is attributed to disorder-activated Raman scattering, whereas the other three modes are assigned to local vibrations of vacancy-related defects.

General expressions for the longitudinal and transverse resistivities of single-crystalline cubic and tetragonal ferromagnets are derived from a series expansion of the resistivity tensor with respect to the magnetization orientation. They are applied to strained (Ga,Mn)As films, grown on (001)-and (113)A-oriented GaAs substrates, where the resistivities are theoretically and experimentally studied for magnetic fields rotated within various planes parallel and perpendicular to the sample surface. We are able to model the measured angular dependences of the resistivities within the framework of a single ferromagnetic domain, calculating the field-dependent orientation of the magnetization by numerically minimizing the free-enthalpy density. Angle-dependent magnetotransport measurements are shown to be a powerful tool for probing both anisotropic magnetoresistance and magnetic anisotropy. The anisotropy parameters of the (Ga,Mn)As films inferred from the magnetotransport measurements agree with those obtained by ferromagnetic resonance measurements within a factor of two.

The frequencies and dampings of the zone-center optical phonons E2 and A1(LO) in wurtzite-type GaN and AlN layers have been measured by Raman spectroscopy in the temperature range from 85 to 760 K. The GaN layer was grown by metalorganic vapor phase epitaxy and the AlN layer by molecular beam epitaxy both on sapphire substrate. The experimentally obtained frequencies and dampings are modeled by a theory taking into account the thermal expansion of the lattice, a symmetric decay of the optical phonons into two and three phonons of lower energy, and the strain in the layers induced by the different thermal expansion coefficients of layer and substrate. The results were used to determine the local temperature of a GaN pn diode in dependence on the applied voltage.

We present a systematic study on the influence of epitaxial strain and hole concentration on the magnetic anisotropy in ͑Ga,Mn͒As at 4.2 K. The strain was gradually varied over a wide range from tensile to compressive by growing a series of ͑Ga,Mn͒As layers with 5% Mn on relaxed graded ͑In,Ga͒As/GaAs templates with different In concentration. The hole density, the Curie temperature, and the relaxed lattice constant of the as-grown and annealed ͑Ga,Mn͒As layers turned out to be essentially unaffected by the strain. Angledependent magnetotransport measurements performed at different magnetic-field strengths were used to probe the magnetic anisotropy. The measurements reveal a pronounced linear dependence of the uniaxial out-of-plane anisotropy on both strain and hole density. Whereas the uniaxial and cubic in-plane anisotropies are nearly constant, the cubic out-of-plane anisotropy changes sign when the magnetic easy axis flips from in-plane to out-of-plane. The experimental results for the magnetic anisotropy are quantitatively compared with calculations of the free energy based on a mean-field Zener model. Almost perfect agreement between experiment and theory is found for the uniaxial out-of-plane and cubic in-plane anisotropy parameters of the as-grown samples. In addition, magnetostriction constants are derived from the anisotropy data.