Ga1−xMnxAs/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 ͓110͔ direction, we quantify the magnetic anisotropy as a function of the voltage V p 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 ͑ 0 H͒ loops are shifted as a function of V p 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 V p applied. Furthermore, we derive the magnetostrictive constant 111 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 voltageinduced irreversible magnetization switching at T = 40 K, which constitutes the basic principle of a nonvolatile memory element.

Ferromagnetic GaAs/GaMnAs Core−Shell Nanowires Grown by Molecular Beam Epitaxy

“…As shown for lithographically generated GaMnAs stripes of similar width, shape anisotropy terms do not play a significant role as the saturation magnetization is small. 54,56 Two basic scenarios are thought to be possible. Either a uniform magnetization forms with a well-defined magnetic anisotropy or the different side facets develop separate magnetic domains which add up to a net magnetization.…”

Voltage-controlled spin mechanics

“…3 exemplarily demonstrate that in ferromagneticferroelectric hybrids, the magnetization orientation can be continuously rotated back and forth within a range of approximately 90°, simply by applying an appropriate electric voltage V p . Indeed, one can show that the reversible voltage control of magnetization orientation is limited to a range of ≤90° in the spin mechanics scheme, given that the external magnetic field strength is kept constant (zero) [10,11]. Furthermore, if the magnetization is prepared into a metastable initial state (a local minimum of F) via a dedicated magnetic field sweep, a one-shot, voltage-controlled, 180° magnetization reversal is possible.…”

“…In spite of vivid research activities, however, single phase magnetoelectric multiferroics still are scarce. An attractive and powerful alternative platform are composite materials, in which an electric-field control of magnetic properties indeed is possible [6,7,8,9,10,11]. Such composites are composed of a ferromagnetic constituent, which shares at least one interface with a ferroelectric (or piezoelectric) material.…”

“…The ferromagnetic constituent (green ellipse) is mechanically connected to the ferroelectric constituent (orange square). In the hybrid sample concept, this connection can be realized via various techniques, e.g., by growing an epitaxial ferromagnetic film onto the ferroelectric [6,7], by evaporating the ferromagnet onto the ferroelectric [11], or by cementing the two constituents together [10]. The only fabrication requirement is to achieve an efficient strain transfer from the ferroelectric into the ferromagnetic constituent.…”

“…(ii) Only ferromagnets with finite (large) magnetostriction qualify for the use in spin mechanics hybrids. (iii) The magnetoelastic contribution to the free enthalpy must be dominant in a given plane of interest -an important constraint in particular for spin mechanics hybrids made from single crystalline ferromagnets [10].…”