Unveiling the role of Co-O-Mg bond in magnetic anisotropy of Pt/Co/MgO using atomically controlled deposition and in situ electrical measurement

Despite the crucial role of interfacial perpendicular magnetic anisotropy in a Co(Fe)/MgO-based magnetic tunnel junction, the underlying mechanism is still being debated. Here, we report an anatomical study of the oxygen and Mg effect on $\mathrm{Pt}/\mathrm{Co}$ bilayers through repeated in situ anomalous Hall effect measurements, controlled oxygen exposure, and Mg deposition in an ultrahigh vacuum system. We found that chemisorbed oxygen not only quenches the effective magnetic moment of the Co surface layer, but also softens its magnetic anisotropy. However, a subsequent Mg dusting on the oxygen preexposed $\mathrm{Pt}/\mathrm{Co}$ surface can recover the magnetic anisotropy. The ab initio calculations on the exchange splitting and orbital hybridization near the Fermi level give a clear physical explanation of the experimental observations. Our results suggest that the Co(Fe)-O-$M$ bond plays a more important role than the widely perceived Co(Fe)-O bond does in realizing interfacial perpendicular magnetic anisotropy in Co(Fe)/MgO heterostructures.