Energetic, electronic, and magnetic properties of Mn pairs on reconstructed (001) GaAs surfaces

Abstract

We study energetic, magnetic, and electronic properties of diluted substitutional Mn-pairs on the reconstructed (001) GaAs surfaces. The studies are based on first-principles calculations in the framework of the density functional theory. We demonstrate that the stability of the systems strongly depends on the position, orientation, and the distance between the Mn-atoms constituting the pair. Independently of the considered surface reconstruction pattern, the Mn-pairs with Mn-atoms being the nearest neighbors (NN) on cationic sublattice turn out to be energetically more favorable than the pairs with the larger distance between the Mn-atoms. However, the preferential build-up orientation of the Mn-NN-pair depends on the surface reconstruction and is parallel either to [110] or [110] crystallographic direction. We reveal also the mechanisms of the magnetic ordering of Mn-NN-pairs. The Mn-NN-pairs along the [110] crystallographic direction exhibit always ferromagnetic alignment of Mn spins, whereas the spins in the Mn-NN-pairs along [110] direction are mostly anti-ferromagnetically aligned. In the electronic structure of the systems containing Mn-pairs with ferromagnetically aligned spins, we observe the valence band hole states in the neighborhood of Fermi energy. This indicates that the surface ferromagnetism in this prototype of dilute magnetic semiconductors can be explained in terms of the p-d Zener model.

In-plane to perpendicular magnetic anisotropy switching in heavily-Fe-doped ferromagnetic semiconductor (Ga,Fe)Sb with high Curie temperature

“…This may be explained by the band structure of heavily-Fe-doped (Ga,Fe)Sb, where the Fermi level (EF) is located in the Fe-related impurity band (IB) in the band gap [41]. Like (Ga,Mn)As, where Mn dimers have preferable orientation along the [1 ̅ 10] axis [42], [43] , we suggest that in (Ga,Fe)Sb there is a preferable Fe distribution along the [1 ̅ 10] axis, thereby making the [1 ̅ 10] axis an easy magnetization axis. However, unlike (Ga,Mn)As [15], [20], there is no four-fold symmetry in the film plane along the <100> axes in the case of (Ga,Fe)Sb.…”

Cubic anisotropy in high homogeneity thin (Ga,Mn)As layers

“…Their sign and magnitude depend in turn on the ratio of valence band splitting to the Fermi energy, and so varies substantially with an effective Mn concentration (x eff = x sub −x I , where x sub is the concentration of substitutional Mn at Ga sites and x I is the concentration of interstitially located Mn species) and temperature (both determine the magnitude of M ), epitaxial strain, and p. It has been generally accepted that in layers where the easy plane configuration is realized, two leading terms are sufficient to adequately describe magnetization processes. They are the crystal symmetry related, fourfold (cubic) component 8 and the Mn-dimers related uniaxial one 37,38 . So, the phenomenological description of the total in-plane magnetostatic energy of the system usually assumes the form:…”