Room temperature ferromagnetism in epitaxial Cr2O3 thin films grown on r-sapphire

We report on the epitaxial growth and magnetic properties of Cr2O3 thin films grown on r-sapphire substrate using pulsed laser deposition. The X-ray diffraction (XRD) (2θ and Φ) and TEM characterization confirm that the films are grown epitaxially. The r-plane (011¯2) of Cr2O3 grows on r-plane of sapphire. The epitaxial relations can be written as [011¯2] Cr2O3 ‖ [011¯2] Al2O3 (out-of-plane) and [1¯1¯20] Cr2O3 ‖ [1¯1¯20] Al2O3 (in-plane). The as-deposited films showed ferromagnetic behavior up to 400 K but ferromagnetism almost vanishes with oxygen annealing. The Raman spectroscopy data together with strain measurements using high resolution XRD indicate that ferromagnetism in r-Cr2O3 thin films is due to the strain caused by defects, such as oxygen vacancies.