Anisotropic Magnetoresistance and Magnetic Anisotropy in High-quality (Ga,Mn)As Films

TL;DR

This study systematically investigates magnetotransport properties of GaMnAs films, revealing how anisotropic magnetoresistance and magnetic anisotropy depend on Mn concentration, annealing, and temperature, with implications for understanding magnetic domain behavior.

Contribution

It provides new insights into the relationship between magnetic anisotropy, annealing, and magnetotransport in high-quality GaMnAs films, highlighting the dominance of uniaxial anisotropy at elevated temperatures.

Findings

AMR decreases with increased magnetic anisotropy and Mn concentration.

Uniaxial magnetic anisotropy is observable from AMR for x >= 0.02.

Planar Hall effect aligns with AMR, indicating single domain behavior.

Abstract

We have performed a systematic investigation of magnetotransport of a series of as-grown and annealed Ga1-xMnxAs samples with 0.011 <= x <= 0.09. We find that the anisotropic magnetoresistance (AMR) generally decreases with increasing magnetic anisotropy, with increasing Mn concentration and on low temperature annealing. We show that the uniaxial magnetic anisotropy can be clearly observed from AMR for the samples with x >= 0.02. This becomes the dominant anisotropy at elevated temperatures, and is shown to rotate by 90o on annealing. We find that the in-plane longitudinal resistivity depends not only on the relative angle between magnetization and current direction, but also on the relative angle between magnetization and the main crystalline axes. The latter term becomes much smaller after low temperature annealing. The planar Hall effect is in good agreement with the measured AMR indicating the sample is approximately in a single domain state throughout most of the magnetisation reversal, with a two-step magnetisation jump ascribed to domain wall nucleation and propagation.