Nature of the Perpendicular-to-Parallel Spin Reorientation in a Mn-doped GaAs Quantum Well: Canting or Phase Separation?

TL;DR

This paper investigates the spin reorientation transition in Mn-doped GaAs quantum wells, revealing that Coulomb energy costs lead to a canted magnetic state rather than phase separation during the transition.

Contribution

It provides a theoretical analysis of the spin reorientation in Mn-doped GaAs quantum wells, highlighting the role of Coulomb energy in preventing phase separation and favoring a canted magnetic state.

Findings

The magnetic anisotropy angle varies continuously with hole concentration.

Quantum well tends toward phase separation but Coulomb energy favors canted states.

Canted magnetic states are stabilized during the transition region.

Abstract

It is well known that the magnetic anisotropy in a compressively-strained Mn-doped GaAs film changes from perpendicular to parallel with increasing hole concentration $p$. We study this reorientation transition at T=0 in a quantum well with Mn impurities confined to a single plane. With increasing $p$, the angle $\theta $ that minimizes the energy $E$ increases continuously from 0 (perpendicular anisotropy) to $\pi /2$ (parallel anisotropy) within some range of $p$. The shape of $\Emin (p)$ suggests that the quantum well becomes phase separated with regions containing low hole concentrations and perpendicular moments interspersed with other regions containing high hole concentrations and parallel moments. However, due to the Coulomb energy cost associated with phase separation, the true magnetic state in the transition region is canted with $0 < \theta < \pi /2$.