Compressive strain induced enhancement of exchange interaction and short-range magnetic order in S r2Ir O4 investigated by Raman spectroscopy

We have carried out Raman spectroscopy experiments to investigate two-magnon excitations in epitaxial thin films of the quasi-two-dimensional antiferromagnetic Mott insulator Sr2IrO4 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 Néel temperature, indicating a strain-induced enhancement of the superexchange interactions between Jeff=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 5d transition-metal oxides.