IMF2017

Much current research is devoted to identify multiferroic materials that possess strongly coupled ferroic properties. So-called “type II" multiferroics attract interest for their magnetically-induced ferroelectricity providing direct coupling of both properties. Since recently, rare earth orthoferrites, RFeO₃ have been considered as such type II multiferroics. Generally speaking, the rich magnetic landscape of rare-earth orthoferrites, including high Néel temperatures (600 K and 700 K), spin reorientations, ordering of the rare-earth sub-lattice and compensation of the two spin lattices, makes these materials potential candidates for magneto-electric coupling. In this work, we focus on SmFeO₃, which has high magnetic transitions temperatures in comparison with other RFeO₃. We have been particularly interested in investigating the coupling of different magnetic orders with the crystal lattice (spin lattice-coupling). For this, we have studied the structural evolution of SmFeO₃ by optical birefringence, Raman spectroscopy and Resonant Ultrasound Spectroscopy, over a wide range of temperature. Besides the well-known magnetic ordering at the Néel temperature and the spin reorientation, we have identified two new anomalies in the signature of spin-lattice coupling and two magnon excitations. Overall, our study illustrates a surprising rich landscape of lattice anomalies of different origin and coupling strength. These structural instabilities are triggered by different magnetic ordering processes and give rise to a multiplicity of possible coupling phenomena, some of which might lead to ferroelectricity.