Enhanced perpendicular magnetic anisotropy through thermal phase transformation in Co/Pd/Ta multilayers

Magnetic multilayers with high uniaxial anisotropy make them suitable for application in spintronic devices needing thermal stability. This investigation demonstrates that annealing at 300 °C can effectively introduce phase transformation of a paramagnetic cobalt oxide (CoO) thin film sandwiched between Pd and Ta layers into a ferromagnetic cobalt (Co) thin film. Reduced multilayers show a large recovery in magnetic moment, enhanced coercivity, and strong perpendicular magnetic anisotropy (PMA). In-plane hysteresis measurements reveal a stronger anisotropic field, highlighting the presence of considerable PMA. Surface roughness rises during annealing, while interface roughness decreases, indicating improved interface quality as confirmed by reflectivity. The rise in electron density implies a shift from CoO to Co which further confirms the reduction. Depth-selective standing wave hard x-ray photoelectron spectroscopy (HAXPES) analysis also confirms the reduction that takes place during thermal annealing and demonstrates the occurrence of the oxide-to-metallic phase transformation. The Co concentrations are significantly greater in bulk regions than in interface locations, showing that the reduction is dominated through bulk Co in the multilayer structure under an effective phase transformation during thermal-induced reduction.