Heat-induced antiferromagnetic coupling in multilayers with ZnSe spacers

Two ferromagnetic films separated by an amorphous semiconducting spacer are exchange coupled across the spacer layer. The coupling is reversibly temperature dependent with a positive temperature coefficient. As spacer material we use amorphous ZnSe which is a compound semiconductor and find heat-induced antiferromagnetic coupling in striking similarity to amorphous Si and Ge. In an Fe/$a$-ZnSe/Fe trilayer with spacer thickness between 18 Å and 22 Å the coupling is antiferromagnetic with a positive temperature coefficient. At slightly larger thicknesses between 22 Å and 25 Å we find a reversible transition from ferromagnetic coupling at low temperatures to antiferromagnetic coupling at higher temperatures upon heating. We discuss the reversibly heat-induced effective exchange coupling in terms of localized defect states in the band gap in the vicinity of the Fermi energy.