Giant magnetoresistance and long-range antiferromagnetic interlayer exchange coupling in (Ga,Mn)As/GaAs:Be multilayers

We report the observation of the giant magnetoresistance effect in semiconductor-based GaMnAs/GaAs:Be multilayers. Clear transitions between low-field-high-resistance and high-field-low-resistance states are observed in selected samples with Be-doped nonmagnetic spacers. These samples also show negative coercive fields in their magnetic hysteresis and antiferromagnetic (AFM) splittings in polarized neutron reflectivity. Our data indicate that the AFM interlayer exchange couplings in this system occur over much longer periods than predicted by current theories, strongly suggesting that the coupling in III-V semiconductor-based magnetic multilayers is significantly longer ranged than in metallic systems.