Torque magnetometry of an amorphous-alumina/strontium-titanate interface

TL;DR

This study uses torque magnetometry to investigate magnetic properties at an amorphous alumina/strontium titanate interface, revealing planar magnetic ordering without the need for internal electric fields, challenging existing models.

Contribution

It demonstrates magnetic ordering at an amorphous oxide interface without polarization, providing new insights into oxide interface magnetism.

Findings

Magnetic response similar to crystalline LAO/STO interfaces

Magnetism observed without internal electric fields

Planar magnetic ordering detected

Abstract

We report torque magnetometry measurements of an oxide heterostructure consisting of an amorphous Al$_2$O$_3$ thin film grown on a crystalline SrTiO$_3$ substrate ($a$-AO/STO) by atomic layer deposition. We find a torque response that resembles previous studies of crystalline LaAlO$_3$/SrTiO$_3$ (LAO/STO) heterointerfaces, consistent with strongly anisotropic magnetic ordering in the plane of the interface. Unlike crystalline LAO, amorphous Al$_2$O$_3$ is nonpolar, indicating that planar magnetism at an oxide interface is possible without the strong internal electric fields generated within the polarization catastrophe model. We discuss our results in the context of current theoretical efforts to explain magnetism in crystalline LAO/STO.