No abstract

We report high resolution x-ray diffraction measurements of (Ga,Mn)As and (Ga,Mn)(As,P) epilayers. We observe a structural anisotropy in the form of stacking faults which are present in the (111) and (111) planes and absent in the (111) and (111) planes. The stacking faults produce no macroscopic strain. They occupy 10 −2 − 10 −1 per cent of the epilayer volume. Full-potential density functional calculations evidence an attraction of MnGa impurities to the stacking faults. We argue that the enhanced Mn density along the common [110] direction of the stacking fault planes produces sufficiently strong [110]/[110] symmetry breaking mechanism to account for the in-plane uniaxial magnetocrystalline anisotropy of these ferromagnetic semiconductors.

The scattering intensity of synchrotron radiation in a compact three‐dimensional volume of the reciprocal space (sinθmax/λ = 0.6283 Å−1) of an SrTiO3 single crystal has been measured at temperatures of 115, 130 and 293 K. The curvilinear features of the diffuse pattern were modelled according to the displacements of both cations correlated along the axis [001]cub (where the subscript cub denotes the cubic structure). The results show that Sr2+ is displaced from the ideal positions along the crystallographic axis [001]cub, forming a short chain composed of about three Sr2+ ions along [001]cub, while the Ti4+ ions are moved in the directions [111]cub, or alternatively [101]cub or [011]cub. The Ti4+ displacements are also correlated along [001]cub, forming a similarly short chain.