Ferromagnetic Resonance study of Spin-phonon Coupling in La_0.7Sr_0.3MnO₃/La_0.7Sr_0.3FeO₃superlattices

Epitaxial La_0.7Sr_0.3MnO₃ (LSMO)/La_0.7Sr_0.3FeO₃ (LSFO) superlattices are ideal perovskite oxide platforms for investigating intriguing interfacial phenomena such as charge transfer, strain relaxation, and ferromagnetic/antiferromagnetic coupling. As a result, the functional properties of LSMO/LSFO superlattice may be tunable via careful substrate engineering. In this work, we utilize the fact that the SrTiO₃ substrate has been shown to present structural phase transitions as a function of temperature to study the magnetic properties of epitaxial LSMO and LSFO thin films as well as LSMO/LSFO superlattices using ferromagnetic resonance (FMR) spectroscopy. We identify strong spin-phonon coupling as evidenced by the gap opening at the crossing points of magnon and phonon bands. Combined with the optical second harmonic generation, we further investigate the impact of the structural phase transitions in the SrTiO₃ substrate on the spin-phonon coupling in LSMO/LSFO superlattices.