Interfacial Fe segregation and its influence on magnetic properties of CoFeB/MgFeO multilayers

We investigated effects of Fe segregation from partially Fe-substituted MgO (MgFeO) on the magnetic properties of CoFeB/MgFeO multilayers. X-ray photoelectron spectroscopy and magnetic measurements revealed that segregated Fe reduced to metallic Fe and ferromagnetism was exhibited at the CoFeB/MgFeO interface. The CoFeB/MgFeO multilayer showed a more than 2-fold enhancement in perpendicular magnetic anisotropy (PMA) energy density compared with that of a standard CoFeB/MgO multilayer. The PMA energy density was further enhanced by insertion of an ultrathin MgO layer between the CoFeB and MgFeO layers. Ferromagnetic resonance measurements also revealed a remarkable reduction of magnetic damping in the CoFeB/MgFeO multilayers.