Magnetic anisotropy in (Ga,Mn)As: Influence of epitaxial strain and hole concentration

Abstract

We present a systematic study on the influence of epitaxial strain and hole concentration on the magnetic anisotropy in ͑Ga,Mn͒As at 4.2 K. The strain was gradually varied over a wide range from tensile to compressive by growing a series of ͑Ga,Mn͒As layers with 5% Mn on relaxed graded ͑In,Ga͒As/GaAs templates with different In concentration. The hole density, the Curie temperature, and the relaxed lattice constant of the as-grown and annealed ͑Ga,Mn͒As layers turned out to be essentially unaffected by the strain. Angledependent magnetotransport measurements performed at different magnetic-field strengths were used to probe the magnetic anisotropy. The measurements reveal a pronounced linear dependence of the uniaxial out-of-plane anisotropy on both strain and hole density. Whereas the uniaxial and cubic in-plane anisotropies are nearly constant, the cubic out-of-plane anisotropy changes sign when the magnetic easy axis flips from in-plane to out-of-plane. The experimental results for the magnetic anisotropy are quantitatively compared with calculations of the free energy based on a mean-field Zener model. Almost perfect agreement between experiment and theory is found for the uniaxial out-of-plane and cubic in-plane anisotropy parameters of the as-grown samples. In addition, magnetostriction constants are derived from the anisotropy data.

Irreversible magnetization switching using surface acoustic waves

“…A linear dependence of the uniaxial anisotropy on strain has indeed been found experimentally using various techniques 22,26,27 . The in-plane uniaxial term B 2// is weakest and corresponds to a minor anisotropy between [110] and [110] axes (details in Annex A).…”

“…For instance, Glunk et. al 22 have shown that the perpendicular uniaxial anisotropy term in (Ga,Mn)(As,P) is proportional to both the out-of-plane strain coefficient ε zz and the hole concentration p. Moreover, contrary to metals, typical precession frequencies of (Ga,Mn)(As,P) can be fairly low, of the order of the GHz in small magnetic fields 5 , which allows good matching to the acoustic wave frequencies provided by SAWs. Finally, the damping parameter can be rather high in this material (α=0.1-0.3 23,24 ) compared to metals (α=0.01 in Ni 80 Fe 20 ), which will limit ringing effects preventing irreversible switching.…”

Scaling relation of the anomalous Hall effect in (Ga,Mn)As

“…Further experimental details concerning the sample growth can be found in Refs. 22,23,24. The samples with high conductivities σ xx >180 Ω −1 cm −1 were obtained by postgrowth annealing for 1 h at 250 • C in air.…”

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

“…[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.…”

“…[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.…”