Ferroelectric control of ferromagnetism in diluted magnetic semiconductors

Abstract

Integration of ferroelectric gates on magnetic semiconductor structures is a challenging problem because of a number of issues including processing incompatibility between these two groups of materials. High interest in such hybrid multiferroic structures is relating to their potential application in new memories and spintronic logic elements. In the present work we demonstrate a structure in which the magnetic response is modulated by the electric field of the poled ferroelectric gate. Such ferroelectric-ferromagnetic bilayer presents potential benefits of nonvolatile electrical switching, low operation voltage and a possibility to modulate the properties in nanoscale via the polarization domain engineering. Earlier nonvolatile electric-field control of ferromagnetism using a ferroelectric gate has been reported in oxide ferromagnetic layers that do not lend themselves to integration with semiconductors. Device-oriented exploration of such systems requires an implementation combining a thin film ferroelectric gate and a commonly-exploited semiconductor suitable for integration in semiconductor devices. Here we report the first ferroelectric gate device demonstrating nonvolatile electric-field-controlled switching of ferromagnetism in a ferroelectric-dilute magnetic semiconductor (DMS) Ga(Mn)As. Specifically, we show that polarization reversal of the gate by a single voltage pulse results in a persistent modulation of the Curie temperature as large as 5%. Such electric-field-driven control of ferromagnetism relies on the mediation of the Mn-Mn exchange interaction by the strongly spin-orbit coupled valence band holes which control both the strength of the magnetic interactions and the magnetocrystalline anisotropies. The Curie temperature TC can thus be a significant function of the hole density p, offering the potential for altering the ferromagnetic response by electric-field control. In a conventional FET system first reported by Ohno et al. control of ferromagnetism requires the application of a large gate voltage and is not persistent. In contrast a ferroelectric gate offers the potential for the large nonvolatile carrier-density control needed in these heavily doped materials, by modest voltages (potentially can be less than 5 V in ultra-thin ferroelectric films). Ferroelectric gates can offer sub-nanosecond response times, and possibility of direct domain writing for reversible modulation of the magnetic properties in submicron scale.