Exchange Coupling in the Ferromagnetic Semiconductor GaMnAs
The study of ferromagnetic semiconductors (FMSs) continues to be of great interest because of their potential for spintronic applications. While there has been much progress in our understanding of FMS materials – particularly of the canonical III-V system Ga1-xMnxAs – many issues still remain unresolved. One of these is the nature of interlayer exchange coupling (IEC) in GaMnAs-based multilayers, an issue that is important from the point of view of possible devices based on spin interactions in such multilayers. In this connection, it is important to establish under what conditions the IEC between successive GaMnAs layers is antiferromagnetic (AFM) or ferromagnetic (FM), since manipulation of such IEC can then be directly applied to achieve giant magnetoresistance (GMR) and other phenomena based on this material.
I will describe magneto-transport, SQUID magnetization, and polarized neutron reflectometry experiments applied to GaMnAs-based tri-layer structures, consisting of GaMnAs layers separated by a non-magnetic GaAs spacer. These measurements serve to identify conditions under which AFM coupling will occur in such GaMnAs/GaAs multilayer systems, thus providing information that can be used for manipulating magnetization as well as GMR in structures based on the ferromagnetic semiconductor GaMnAs.