Heat-activated magnetic exchange coupling across Ge barriers and Ge/Si heterostructures

We report the observation of thermally activated exchange coupling across amorphous germanium barriers. At T=50 K the coupling persists up to ${\mathit{d}}_{\mathrm{Ge}}$=60 Å. Heat input reversibly enhances the coupling strength. The exchange across a-Ge always is ferromagnetic. Experiments with Ge/Si heterostructures show that the occurrence of antiferromagnetic coupling requires the presence of some a-Si in the barrier and a total spacer thickness of ∼20 Å. Results indicate that the density of defect states determines the nature of the coupling through amorphous semiconductors.