Compressive-strain induced enhancement of exchange interactions and short-range magnetic order in Sr$_2$IrO$_4$ investigated by Raman spectroscopy

TL;DR

This study demonstrates that applying compressive strain to Sr$_2$IrO$_4$ thin films enhances exchange interactions and short-range magnetic order, as shown by Raman spectroscopy and supported by density functional theory calculations.

Contribution

It provides the first combined experimental and theoretical evidence of strain-induced enhancement of magnetic exchange interactions in Sr$_2$IrO$_4$ thin films.

Findings

Two-magnon peak energy increases with compressive strain

Enhanced magnetic interactions observed over wider temperature range

Density functional theory confirms increased hopping and exchange with strain

Abstract

We have carried out Raman spectroscopy experiments to investigate two-magnon excitations in epitaxial thin films of the quasi-two-dimensional antiferromagnetic Mott insulator Sr$_2$IrO$_4$ under in-plane misfit strain. With in-plane biaxial compression, the energy of the two-magnon peak increases, and the peak remains observable over a wider temperature range above the N\'eel temperature, indicating strain-induced enhancement of the superexchange interactions between $\it{J}_{eff}$ = 1/2 pseudospins. From density functional theory calculations, we have found an increase of the nearest-neighbor hopping parameter and exchange interaction with increasing biaxial compressive strain, in agreement with the experimental observations. Our experimental and theoretical results provide perspectives for systematic, theory-guided strain control of the primary exchange interactions in 5$\it{d}$ transition metal oxides.