In-plane uniaxial anisotropy rotations in (Ga,Mn)As thin films

Abstract

We show, by SQUID magnetometry, that in (Ga,Mn)As films the in-plane uniaxial magnetic easy axis is consistently associated with particular crystallographic directions and that it can be rotated from the [-110] direction to the [110] direction by low temperature annealing. We show that this behavior is hole-density-dependent and does not originate from surface anisotropy. The presence of uniaxial anisotropy as well its dependence on the hole-concentration and temperature can be explained in terms of the p-d Zener model of the ferromagnetism assuming a small trigonal distortion.Comment: 4 pages, 6 Postscript figures, uses revtex

Spin-orbit coupling effect in (Ga,Mn)As films: Anisotropic exchange interactions and magnetocrystalline anisotropy

“…So far, however, to the best of our knowledge, there is no consensus in the literature concerning the origin of the in-plane uniaxial anisotropy. Although in some recent theoretical works the origin of the uniaxial in-plane anisotropy is attributed to a trigonal distortion caused by a uniaxial or shear strain within the film plane, 13,18,21 this type of distortion was not observed experimentally. Recently, Werpachowska and Dietl 22 suggested that the anisotropy mechanism in (Ga,Mn)As films originates from Dzyaloshinsky-Moriya interactions, without assuming any in-plane lattice distortion within their model.…”

“…[11][12][13][14][15][16][17][18] In spite of different experimental conditions, the in-plane uniaxial anisotropy was observed for (Ga,Mn)As films in a thickness range from 25 nm (Ref. 20) to 500 nm, 16 irrelevant with respect to the surface condition.…”

“…[7][8][9][10][11][12][13][14][15][16][17] As soon as the spin polarization of the valence bands becomes rather small, the MCA in (Ga,Mn)As is discussed in terms of anisotropic exchange interactions of the Mn atoms. 2,3,7 The strength of the MCA depends on the hole concentration introduced by the Mn impurity atoms 2,11,18,19 as well as on the variation of the equilibrium lattice parameter of (Ga,Mn)As, which increases with increasing Mn content and results thus in a larger lattice mismatch with the GaAs substrate.Numerous experimental results evidenced a temperature-induced transition from the biaxial to the uniaxial in-plane anisotropy in (Ga,Mn)As films deposited on GaAs. [11][12][13][14][15][16][17][18] In spite of different experimental conditions, the in-plane uniaxial anisotropy was observed for (Ga,Mn)As films in a thickness range from 25 nm (Ref.…”

“…2,3,7 The strength of the MCA depends on the hole concentration introduced by the Mn impurity atoms 2,11,18,19 as well as on the variation of the equilibrium lattice parameter of (Ga,Mn)As, which increases with increasing Mn content and results thus in a larger lattice mismatch with the GaAs substrate.…”

Prospects for high temperature ferromagnetism in (Ga,Mn)As semiconductors

“…The model also accounts for strong spin-orbit interaction present in the host valence band which splits the three p bands into a heavyhole, light-hole, and a split-off band with different dispersions. The spin-orbit coupling is not only responsible for a number of distinct magnetic [25][26][27][28] and magneto-transport [29][30][31][32] properties of ͑Ga,Mn͒As ferromagnets but the resulting complexity of the valence band was shown 14,33 to play also an important role in suppressing magnetization fluctuation effects and, therefore, stabilizing the ferromagnetic state itself. On the other hand, describing the potentially complex behavior of Mn Ga in GaAs by a single parameter may oversimplify the problem.…”