Electron leakage and double-exchange ferromagnetism at a prototype metal-insulator interface: CaRuO$_3$/CaMnO$_3$

Density-functional studies of the electronic structure of a prototype interface between a paramagnetic metal and an antiferromagnetic insulator (CaRuO$_3$/ CaMnO$_3$) reveal how magnetism near the interface can be modified by the leaked electrons from the metallic to the insulating side. These electrons mediate a ferromagnetic interaction between the interface Mn moments via Anderson-Hasegawa double-exchange, which competes with the already existing antiferromagnetic superexchange, resulting in an interfacial ferromagnetic layer. Electron penetration beyond the first layer is insufficient to alter the bulk antiferromagnetism. We argue that a canted state in the first layer is possible, consistent with earlier magnetic measurements on this system.