Anomalous exchange coupling in transition-metal-oxide based superlattices with antiferromagnetic spacer layers

Abstract

A direct correlation is seen between the coercive field (H_C) and the magnetic-field-dependent resistivity (MR) in SrMnO₃/SrRuO₃ superlattices of perpendicular magnetic anisotropy. The magnetoresistance shows a sharp jump at H_C for in-plane current and the out-of-plane magnetic field. Both H_C and high-field MR also oscillate with the thickness of the SrMnO₃ spacer layers separating the metallic ruthenate. Since the spacer in these superlattices has no mobile carriers to facilitate an oscillatory coupling, we attribute the observed behavior to the spin-polarized quantum tunneling of electrons between the ferromagnetic layers and antiferromagnetically ordered t_2g spins of SrMnO₃.