Control of the perpendicular magnetic anisotropy and perpendicular exchange bias in CoPt/CoOx thin films

Abstract

Abstract The magnetic properties of the CoPt/CoOx bilayers have been investigated in this work. Compared with the CoPt single layer, enhanced perpendicular magnetic anisotropy (PMA) and strong perpendicular exchange bias (PEB) have been observed in the CoPt/CoOx bilayers. The thin CoOx layer with Co at different oxidization state, formed by controlling the oxygen gas flow rate ratio in the oxygen and argon gas mixture during the magnetron sputtering, has been found to significantly affect the magnetic anisotropy and exchange bias of the films. Up to 20% oxygen flow rate ratio, the oxidization of Co in CoOx layer monotonously promotes the PMA. While the maximum value of PEB is obtained at 10% oxygen flow rate ratio, and then decreases for further oxidation due to the phase transition from CoO to Co3O4 with a smaller AFM anisotropy constant. Our study provides useful information for fabricating and understanding ferromagnet/antiferromagnet thin films with strong perpendicular magnetic anisotropy and perpendicular exchange bias.