Anomalous behaviour of phonon modes – Magnetic properties correlations in La_0.7Sr_0.3MnO₃/SrRuO₃ superlattices

Artificial superstructure of (111) oriented La_0.7Sr_0.3MnO₃ (LSMO)/SrRuO₃ (SRO) were grown on (111) oriented SrTiO₃ substrate using pulsed laser deposition.Microstructure quality and coherency of interafaces were studied using high resolution transmission electron microscopy .The growth epitaxy, crystalline quality,crystal structure and artificial bilayer periodicity of these superlattices were studied using x-ray diffraction. The cumulative strain in these superlattices was studied from the reciprocal space mapping (RSM) .The RSM image of these superlattices indicates relaxation in some crystallographic directions.The magnetic exchange coupling at the interfaces of the LSMO-SRO has been investigated with the in-plane and the out-of-plane oriented magnetic field. The phonon mode anomaly of these superlattices were observed in the temperature dependent frequencies of the Raman lines. The observed peak at around 160 K and step like anomaly at around 350 K of the Raman peak frequencies provide strong evidence of magnetic phase transition of SRO and LSMO respectively. The observed anomalies in phonon modes in Raman scattering are discussed in terms of spin phonon coupling and delocalization of polaronic states in the vicinity of magnetic phase transition temperature of LSMO and SRO.