Experimental determination of next-nearest-neighbor interlayer exchange coupling in ferromagnetic GaMnAs/GaAs:Be multilayers

We report direct experimental determination of next-nearest-neighbor (NNN) interlayer exchange coupling (IEC) in antiferromagnetically coupled GaMnAs/GaAs:Be multilayers. Magnetoresistance in such multilayers shows step-like transitions as a function of applied magnetic field that corresponds to abrupt changes of spin configuration. By adjusting the field range, one obtains minor hysteresis loops that allow one to determine spin configurations occurring in the multilayer, which in turn can be used to obtain the ratio of NNN IEC to NN IEC. By using this method on a series of GaMnAs/GaAs:Be with different numbers of GaMnAs layers, we obtain this ratio to be 0.23, in good agreement with theoretical predictions.