Ferromagnetic exchange, spin-orbit coupling and spiral magnetism at the LaAlO_3/SrTiO_3 interface

TL;DR

This paper develops a microscopic theory explaining how local magnetic moments and spiral magnetism emerge at the LaAlO_3/SrTiO_3 interface, influenced by spin-orbit coupling and external fields, with predictions aligning with experimental observations.

Contribution

It introduces a novel microscopic model linking orbital splitting, spin-orbit coupling, and magnetic order at the interface, providing insights into the origin of magnetism in non-magnetic oxide heterostructures.

Findings

Correlation-induced local moments arise from orbital splitting.

Gate-tunable Rashba spin-orbit coupling affects exchange interactions.

Predicted spiral magnetic ground state matches experimental torque data.

Abstract

The electronic properties of the polar interface between insulating oxides is a subject of great current interest. An exciting new development is the observation of robust magnetism at the interface of two non-magnetic materials LaAlO_3 (LAO) and SrTiO_3 (STO). Here we present a microscopic theory for the formation and interaction of local moments, which depends on essential features of the LAO/STO interface. We show that correlation-induced moments arise due to interfacial splitting of orbital degeneracy. We find that gate-tunable Rashba spin-orbit coupling at the interface influences the exchange interaction mediated by conduction electrons. We predict that the zero-field ground state is a long-wavelength spiral and show that its evolution in an external field accounts semi-quantitatively for torque magnetometry data. Our theory describes qualitative aspects of the scanning SQUID measurements and makes several testable predictions for future experiments.