Emergent Magnetism at the 3$d$-5$d$ Interface: SrMnO$_3/$SrIrO$_3$

TL;DR

This study uses density-functional theory to investigate the emergent ferromagnetism at the interface of SrMnO3 and SrIrO3, revealing charge transfer-induced magnetic phase changes driven by strong spin-orbit coupling and double exchange physics.

Contribution

The paper provides a detailed theoretical analysis of interfacial magnetism in a SrMnO3/SrIrO3 superlattice, highlighting the role of charge transfer and electron doping in inducing ferromagnetism.

Findings

Interfacial charge transfer turns both materials into ferromagnetic metals.

Doped electrons in SMO induce ferromagnetism via double exchange.

SIO becomes ferromagnetic due to doping of a Mott-Hubbard insulator.

Abstract

Recent experiments have found new magnetic behaviors, which are different from the parent bulk materials, at the interfaces between 3$d$ and 5$d$ oxides such as SrMnO$_3$ (SMO) and SrIrO$_3$ (SIO). The system is of considerable interest due to the strong spin-orbit coupling in the 5$d$ materials on one hand and the double exchange physics in SMO on the other, which belongs to the class of the colossal magnetoresistive (CMR) manganites. In order to gain insight into the physics of the system, we have performed density-functional studies on a selected interface structure, viz., the (SMO)$_1$(SIO)$_1$ superlattice, which has been experimentally grown and studied. Our density-functional results show that the interfacial magnetism is controlled by a net charge transfer at the interface from the SIO to the SMO side, turning both of them into ferromagnetic metal from the original antiferromagnetic insulating state in the bulk. The transferred electrons to the SMO side make it ferromagnetic through the Anderson-Hasegawa double exchange interaction, while the SIO part becomes ferromagnetic due to the doping of the half-filled Mott-Hubbard insulator as suggested by the Nagaoka Theorem. Our results are discussed in the context of the experiments for the same structure.