Polarity and charge redistribution induced emergent interfacial ferromagnetism in non-magnetic LaNiO3/SrMnO3 superlattices

Artificial heterostructures composed of strongly correlated oxides can host many up-and-coming phenomena. The interfacial ferromagnetism can be observed at the interface of paramagnetic LaNiO3 (LNO) and G-type antiferromagnetic SrMnO3 (SMO). Through the macroscopic magnetic and transport measurements and the microscopic x-ray magnetic circular dichroism signals, the obvious interfacial ferromagnetic behavior exhibited in the thicker superlattices. Using x-ray absorption spectroscopy and x-ray photoelectron spectroscopy measurements, the polar mismatch-induced charge redistribution in Ni and Mn ions accurately demonstrates the dependence on the varying thickness of LNO/SMO superlattices. These results suggest that the ferromagnetic double-exchange interaction of Mn3+–Mn4+ increases and the ferromagnetic super-exchange interaction of Ni2+–Mn4+ decreases with the increasing thickness of LNO/SMO superlattices. Consequently, the obvious ferromagnetic behavior in the thicker superlattices is induced by the double-exchange interaction. For the thinner LNO/SMO superlattice, the interfacial super-exchange ferromagnetic state is offset by the double-exchange ferromagnetism. This is the crucial reason behind the fact that ferromagnetism is hard to exist in the prior LNO/SMO superlattices. Our findings highlight the intrinsic mechanism responsible for the interfacial ferromagnetism and the significance of understanding polar mismatch at the interface of heterostructures.