Ga_1−xMn_xAs/piezoelectric actuator hybrids : A model system for magnetoelastic magnetization manipulation

Abstract

We have investigated the magnetic properties of a piezoelectric actuator/ferromagnetic semiconductor hybrid structure. Using a GaMnAs epilayer as the ferromagnetic semiconductor and applying the piezo stress along its [110] direction, we quantify the magnetic anisotropy as a function of the voltage Vp applied to the piezoelectric actuator using anisotropic magnetoresistance techniques. As the magnetic anisotropy in GaMnAs substantially changes as a function of temperature T, the ratio of the magnetoelastic and the magnetocrystalline anistropies can be tuned from approximately 1/4 to 4. Thus, GaMnAs/piezoelectric actuator hybrids are an ideal model system for the investigation of different piezoelastic magnetization control regimes. At T=5 K the magnetoelastic term is a minor contribution to the magnetic anisotropy. Nevertheless, we show that the switching fields of ρ(μ0H) loops are shifted as a function of Vp at this temperature. At 50 K—where the magnetoelastic term dominates the magnetic anisotropy—we are able to tune the magnetization orientation by about 70° solely by means of the electrical voltage Vp applied. Furthermore, we derive the magnetostrictive constant λ111 as a function of temperature and find values consistent with earlier results. We argue that the piezo voltage control of magnetization orientation is directly transferable to other ferromagnetic/piezoelectric hybrid structures, paving the way to innovative multifunctional device concepts. As an example, we demonstrate piezo voltage-induced irreversible magnetization switching at T=40 K, which constitutes the basic principle of a nonvolatile memory element.