Reversible magneto-ionics in crystallized W–Co20Fe60B20–MgO–HfO2 ultra-thin films with perpendicular magnetic anisotropy

We have investigated the electric field (E-field) induced modulation of perpendicular magnetic anisotropy (PMA) in both amorphous and crystalline W/CoFeB/MgO/HfO2 ultra-thin films. We find that in the amorphous state, the E-field effect is volatile and reversible, which is consistent with the conventional electrostatic effect through charge accumulation and depletion. In the crystallized system annealed at 370 °C, we find that two effects are at play: a non-volatile and reversible voltage-induced effect on PMA and an electrostatic response. We discuss these results in terms of higher oxygen mobility at the crystallized CoFeB–MgO interface, which induces a non-volatile magneto-ionic response. Modulating PMA in crystallized CoFeB–MgO materials through ionic migration opens the path to integrating magneto-ionics in full magnetic tunnel junctions.