Origin of perpendicular magnetic anisotropy in CoxFe3-xO4+δ thin films studied by x-ray magnetic circular and linear dichroisms

We investigate the element-specific spin and orbital states and their roles in magnetic anisotropy in Co-ferrite [CoxFe3-xO4+delta (001)] thin films which exhibit perpendicular magnetic anisotropy (PMA). The origin of PMA in the low-x region (x < 1) can be mainly explained by the large perpendicular orbital magnetic moments in the Co2+ (3d(7)) states detected by x-ray magnetic circular dichroism and x-ray magnetic linear dichroism (XMLD). The XMLD for a PMA film (x = 0.2) with a square hysteresis curve shows the oblate charge distribution in the Co2+ site, which is consistent with the change in local nearest-neighbor distance in Co detected by extended x-ray absorption fine structure analysis. Our finding reveals that the microscopic origin of PMA in Co ferrite comes from the enhanced orbital magnetic moments along the out-of-plane [001] direction through in-plane charge distribution by tensile strain, which adds the material functionalities in spinel ferrite thin films from the viewpoint of strain and orbital magnetic moments.