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

TL;DR

This study systematically investigates how epitaxial strain and hole concentration affect magnetic anisotropy in (Ga,Mn)As at low temperature, revealing linear dependencies and sign changes in anisotropy components, with results matching theoretical models.

Contribution

It provides a comprehensive experimental and theoretical analysis of magnetic anisotropy dependence on strain and hole density in (Ga,Mn)As, highlighting the linear relationship and sign reversal of anisotropy components.

Findings

Uniaxial out-of-plane anisotropy depends linearly on strain and hole density.

Cubic out-of-plane anisotropy changes sign when magnetic easy axis flips.

Experimental results agree well with mean-field Zener model calculations.

Abstract

We present a systematic study on the influence of epitaxial strain and hole concentration on the magnetic anisotropy in (Ga,Mn)As at 4.2 K. The strain was gradually varied over a wide range from tensile to compressive by growing a series of (Ga,Mn)As layers with 5% Mn on relaxed graded (In,Ga)As/GaAs templates with different In concentration. The hole density, the Curie temperature, and the relaxed lattice constant of the as-grown and annealed (Ga,Mn)As layers turned out to be essentially unaffected by the strain. Angle-dependent 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. An 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.