Robust room temperature ferromagnetism in epitaxial CoO thin film

Co vacancy (V_Co) induced robust room temperature ferromagnetism (Ms ∼ 60 emu/cm³ and coercivity ∼ 603 Oe) is experimentally realized in rock-salt CoO epitaxial thin film (∼110 nm) grown by pulsed laser deposition. Co charge state is found to be higher ∼+3.2 (from Co L₃/L₂ white line ratio) and this is due to the V _Co induced charge transfer from the neighboring Co-3d to O-2p states in order to compensate for the hole formation. O-K and cathodoluminescence spectra corroborate the existence of V_Co and higher charge state. Temperature dependent magnetization and exchange bias experiments confirm the coexistence of ferromagnetic and antiferromagnetic phases.