Magnetism in artificial Ruddlesden-Popper iridates leveraged by structural distortions

TL;DR

This study demonstrates how structural distortions in artificial iridate superlattices significantly influence magnetic interactions, revealing tunable magnetic properties akin to bulk Ruddlesden-Popper iridates through heterostructuring.

Contribution

It shows that subtle structural modulations in iridate superlattices can be leveraged by spin-orbit coupling to alter magnetic interactions, providing a new approach to engineering magnetic properties.

Findings

Magnetic moments are predominantly c-axis antiferromagnetic in bilayer superlattices.

Magnon gaps are observed and reduced in the superlattice compared to bulk analogues.

Structural bending affects anisotropic exchange interactions, influencing magnetic behavior.

Abstract

We report on the tuning of magnetic interactions in superlattices composed of single and bilayer SrIrO$_3$ inter-spaced with SrTiO$_3$. Magnetic scattering shows predominately $c$-axis antiferromagnetic orientation of the magnetic moments for the bilayer justifying these systems as viable artificial analogues of the bulk Ruddlesden-Popper series iridates. Magnon gaps are observed in both superlattices, with the magnitude of the gap in the bilayer being reduced to nearly half that in its bulk structural analogue, Sr$_3$Ir$_2$O$_7$. We assign this to modifications in the anisotropic exchange driven by bending of the $c$-axis Ir-O-Ir bond and subsequent local environment changes, as detected by x-ray diffraction and modeled using spin wave theory. These findings explain how even subtle structural modulations driven by heterostructuring in iridates are leveraged by spin orbit coupling to drive large changes in the magnetic interactions.