Giant voltage-controlled magnetic anisotropy effect in a crystallographically strained CoFe system

We experimentally demonstrate a giant voltage-controlled magnetic anisotropy (VCMA) coefficient in a crystallographically strained CoFe layer (∼15 monolayers in thickness) in a MgO/CoFe/Ir system. We observed a strong applied voltage dependence of saturation field and an asymmetric concave behavior with giant VCMA coefficients of −758 and 1043 fJ V−1 m−1. The result of structural analysis reveals epitaxial growth in MgO/CoFe/Ir layers and the orientation relationship MgO(001)[110] CoFe(001)[100] Ir(001)[110]. The CoFe layer has a bcc structure and a tetragonal distortion due to the lattice mismatch; therefore, the CoFe layer has a large perpendicular magnetic anisotropy.