Temperature dependent Raman scattering and electronic transitions in rare earth SmFeO3

Abstract

Emerging interdisciplinary fields of multiferroics and spin-optronics demand for new oxide materials that unfolds significant coupling between electric and magnetic order at room temperature, preferably with controlled optical properties. Rare-earth orthoferrites (RFeO3) have received much attention due to their coupled electric, magnetic and optic properties. Here we report structural, optical, temperature-dependent (83–800K) Raman spectroscopy, electronic transition analysis and electric poling induced magnetic modulation in nanostructured SmFeO3 (SFO). Rietveld refinement of SFO confirmed the orthorhombic phase (space group D2h16, Pbnm) with expanded lattice parameters (ao = 5.3979Å < bo = 5.5922 Å < co = 7.7104Å). Microstructural analysis revealed the formation of uniformly distributed spherical grains of 40 ± 2nm size. First-order 18 Raman active vibrational phonon modes identified using damped harmonic oscillator model suggested the main activity in SFO lies between 100 and 650cm−1. Above 483K, clear fading of high frequency mode (~ 632cm−1) due to spin-reorientation and fusion in low frequency modes (~132cm−1) around 673K is considered as direct evidence of possible phase transition from antiferromagnetic to paramagnetic order. Optical response in studied spectral range from 200 to 800nm is dominated by two (p-d) and (d-d) charge transfer transitions, which favors strong exchange interaction as well as high magnetic transition temperatures. Large observed bandgap Eg of 5.21eV, determined from diffuse reflectance Uv–visible spectroscopy in combination with the electric poling induced magnetic modulation establish SFO, a suitable oxide material for future power efficient microelectronic and spin-optoelectronic devices.