Experimental observation of spin-phonon coupling in Cr2O3 and Fe2O3 solid solution and bandgap engineering

Abstract

In this work, we present experimental evidence of spin-phonon coupling at room temperature in the solid solutions of Cr2O3 and Fe2O3. The bulk ceramics of Cr2-xFexO3 were fabricated by sol–gel method. The corundum crystal structure with R-3c space group confirmed by Reitveld refinement. Spin-flop transitions observed in the 100–400 K temperature ranges from M−H studies were observed in the lower doping range. The magnetic transition observed from the temperature dependent magnetic studies showed the transition is consistent with the previous reports. The spin-phonon coupling in the ceramics is observed from the two phonon modes in the materials originating from Eg and A1g modes in the Raman spectroscopy. Eg mode shifts towards lower frequency, while A1g mode shifts towards high frequency. UV–vis spectral studies revealed the narrowing of bandgap originating from the Cr-O-Fe hybridisation. Impedance spectroscopy analysis shows that relaxation peaks shift from 90 K to 240 K towards high temperatures. The activation energy value is 0.32 – 0.21 eV, indicating the polaron hopping conductivity in the bulk ceramics.