Nature of weak magnetism in SrTiO3/LaAlO3 multilayers

TL;DR

This study uses nuclear magnetic resonance to reveal that weak magnetism at LaAlO3/SrTiO3 interfaces depends on spacer layer thickness, with magnetic moments emerging above a critical thickness of 4-6 unit cells.

Contribution

It demonstrates the thickness-dependent emergence of weak magnetism at LaAlO3/SrTiO3 interfaces using beta-detected NMR, revealing the role of spacer layer thickness.

Findings

Magnetism appears only when spacer layer exceeds 3 unit cells.

Relaxation rates peak near 35 K indicating slowing electronic moments.

Minimal magnetic moments are about 0.002 μB.

Abstract

We report the observation of weak magnetism in superlattices of LaAlO3/SrTiO3 using beta-detected nuclear magnetic resonance. The spin lattice relaxation rate of 8 Li in superlattices with a spacer layers of 8 and 6 unit cells of LaAlO3 exhibits a strong peak near ~35 K, whereas no such peak is observed in a superlattice with spacer layer thickness of 3 unit cells. We attribute the observed temperature dependence to slowing down of weakly coupled electronic moments at the LaAlO3/SrTiO3 interface. These results show that the magnetism at the interface depends strongly on the thickness of the spacer layer, and that a minimal thickness of ~4-6 unit cells is required for the appearance of magnetism. A simple model is used to determine that the observed relaxation is due to small fluctuating moments (~0.002 muB) in the two samples with a larger LaAlO3 spacer thickness.