Dynamics of electron density, spin-phonon coupling, and dielectric properties of SmFeO3 nanoparticles at the spin-reorientation temperature: Role of exchange striction

Samarium orthoferrite (SmFeO3) has been the subject of debate on the existence or nonexistence of ferroelectric properties. It has a high spin-reorientation transition temperature T-SR (480 K). Detailed synchrotron x-ray diffraction and Raman spectroscopy dielectric investigations in the 300 to 600 K temperature range of SmFeO3 nanoparticles (similar to 65 nm) have been performed. Raman spectroscopy established the existence of strong spin-phonon coupling and magnetostriction in the system. Magnetic measurements showed a spin-reorientation transition region from 480 to 450 K similar to that of a single crystal. The dielectric constant confirmed a clear anomaly around T-SR. The signature of unusual relaxor ferroelectric behavior in SmFeO3 nanoparticles from 380 to 480 K was observed in the dielectric properties. The electron density plots obtained using Rietveld refinement of the synchrotron x-ray diffraction data showed the displacement of the Sm and Fe ions, which can play a key role in the anomalous behavior at T-SR. The analysis indicated the presence of magnetoelectric coupling due to the exchange interaction between Sm and Fe spins in SmFeO3 nanoparticles.