Magnetic and Chemical Depth Profiles of an Exchange-Biased MnO/GaMnAs Bilayer

There is a great deal of interest in development of high Curie temperature (Tc) ferromagnetic (FM) semiconductors for use in spintronic applications. GaMnAs may be a candidate for such applications, as it shows true long range FM order among Mn at Ga sites, and has a relatively high Tc (up to 173 K). For many device applications, the ability to pin the magnetization of a FM semiconductor to a preferred direction is highly desirable. This can be achieved by exchange coupling a GaMnAs layer to an adjacent antiferromagnetic (AFM) layer in order to produce an exchange-bias in the FM layer. We report on polarized neutron reflectivity and x-ray reflectivity studies of a GaMnAs film exchange biased by an AFM MnO overlayer. Using the depth sensitivity of these reflectivity techniques, we have chemically and magnetically characterized the MnO/GaMnAs interface, and have investigated the magnetization reversal process by comparing the magnetic depth profile at the coercive field to the profile at magnetic saturation.