Interlayer coupling and magnetoresistance in FeSi multilayers with semiconducting spacers

Two different types of antiferromagnetic (AF) interlayer coupling as a function of Si layer thickness t_Si were observed in a series of (2.6 nm Fe-t_Si nm Si)₂₂ multilayers prepared by ion beam sputtering on thermally oxidized Si substrates. One AF coupling was observed around t_Si = 1.2 nm at room temperature and changed into ferromagnetic (F) coupling at low temperature. This phenomenon was ascribed to a narrow gap semiconductor with impurity states in the energy gap formed at the interface. The other AF coupling was observed for t_Si thicker than 1.5 nm Si, with a minimum around t_Si = 2.5 nm, which was almost temperature independent; this was attributed to the formation of an amorphous Si layer for the thicker Si layers. Negative magnetoresistance was observed in the multilayers with AF coupling, which had a similar temperature dependence to that of the AF coupling.