Fyzikální ústav Akademie věd ČR

Significance of thin layers of ferromagnetic semiconductors (Ga,Mn)As for applications in spintronics is based on their magnetocrystalline anisotropy. While the orientation of an easy magnetic axis along the layer plane and its change to normal direction in case of Bravais lattice deformation is well understood, the origin of surface uniaxial anisotropy, that means non-equivalence of [110] and [¯110] directions, has not been resolved yet. In this work we explained possible microscopical mechanism of this effect. We report on high-resolution x-ray diffraction measurements of (Ga,Mn)As and (Ga,Mn)(As,P) epilayers. We observed a structural anisotropy in the form of stacking faults that are present in the (111) and (111¯) planes and absent in the (1¯11) and (11¯1) planes. They occupy 10⁻²%–10⁻¹% of the ferromagnetic epilayer volume while no stacking faults are detected in the controlled, undoped GaAs epilayer. Full-potential density functional calculations provide additional evidence that the formation of the stacking faults is promoted by Mn attracted to these structural defects. The enhanced Mn density along the common [11¯0] direction of the stacking fault planes produces a symmetry-breaking mechanism of a strength and sense that can account for the uniaxial [110]/[11¯0] magnetocrystalline anisotropy of these ferromagnetic semiconductors.

Energy of the system decreases when an Mn atom is localized in a close proximity of the defect.

¹Institute of Physics ASCR, v. v. i., Na Slovance 2, 182 21 Prague 8, Czech Republic
²School of Physics and Astronomy, University of Nottingham, Nottingham NG7 2RD, United Kingdom
³Institute of Physics ASCR, v. v. i., Cukrovarnická 10, 162 53 Praha 6, Czech Republic