RESUMO
Density functional theory (DFT) calculations of the energy of magnetic anisotropy for diluted ferromagnetic semiconductor Ge(1-x)Mn(x)Te were performed using OpenMX package with fully relativistic pseudopotentials. The influence of hole concentration and magnetic ion neighbourhood on magnetic anisotropy energy is presented. Analysis of microscopic mechanism of magnetic anisotropy is provided, in particular the role of spin-orbit coupling, spin polarization and spatial changes of electron density are discussed. The calculations are in accordance with the experimental observation of perpendicular magnetic anisotropy in rhombohedral Ge(1-x)Mn(x)Te (1 1 1) thin layers.
RESUMO
The temperature dependence of the magnetic specific heat of the semimagnetic semiconductor Pb(1-x)Gd(x)Te for x = 0.033 and 0.054, over the temperature range from 0.5 to 10 K, in magnetic fields up to 2 T, has been measured and analyzed theoretically. The maxima of the magnetic specific heat in nonzero magnetic fields are shifted to lower temperatures in comparison with theoretical predictions based on the simple cluster model. We propose a mechanism which explains these shifts. According to our model, they are caused by strong hybridization of the 5d shell of gadolinium with band states of the crystal.
RESUMO
In mixed crystals, because of the different ionic radii of cations or anions and the randomness in the placement of ions of different kinds, the crystal lattice is locally deformed. Such local deformations have significant influence on the ground state splitting of magnetic ions. Because this ground state splitting is responsible for the position of the electron paramagnetic resonance (EPR) lines, microscopic disorder is one of the factors which lead to the broadening of the lines, and eventually to their disappearance. This paper is devoted to semi-quantitative analysis of the influence of microscopic disorder on EPR spectra. The theory is compared against measurements performed on mono-crystalline Pb(1-x)Ge(x)Te epitaxial layers containing Eu(2+) ions for different germanium and europium contents. With increasing germanium content we observe gradual disappearance of the EPR lines, although macroscopically, on the basis of x-ray diffraction analysis, each layer might have been considered as a perfect crystal.
RESUMO
We fabricated a hybrid structure in which cobalt and permalloy micromagnets produce a local in-plane spin-dependent potential barrier for high-mobility electrons at the GaAs/AlGaAs interface. Spin effects are observed in ballistic transport in the range of tens of mT of the external field and are attributed to switching between Zeeman and Stern-Gerlach modes--the former dominating at low electron densities.
