Definitive evidence of interlayer coupling between Ga_1−xMn_xAs layers separated by a nonmagnetic spacer

We have used polarized neutron reflectometry to study the structural and magnetic properties of the individual layers in a series of AlGaAs:Be∕Ga_1−xMn_xAs∕GaAs∕Ga_1−xMn_xAs multilayer samples. Structurally, we observe that the samples are virtually identical except for the GaAs spacer thickness (which varies from 3 to 12 nm), and confirm that the spacers contain little or no Mn. Magnetically, we observe that for the sample with the thickest spacer layer, the Ga_1−xMn_xAs layer adjacent to the Be-doped AlGaAs cap has a temperature dependent magnetization very different from that of the other Ga_1−xMn_xAs layer. However, as the spacer layer thickness is reduced, the temperature dependent magnetizations of the two Ga_1−xMn_xAs layers become progressively more similar—a trend we find to be independent of the crystallographic direction along which spins are magnetized. These results definitively show that Ga_1−xMn_xAs layers can couple across a nonmagnetic spacer and that such coupling depends on spacer thickness.