Tuning of ferrimagnetism and perpendicular magnetic anisotropy in NiC o2 O4 epitaxial films by the cation distribution

Cation distribution in transition-metal oxides is closely tied to their physical properties. Here we employed resonant x-ray-diffraction technique and quantitatively evaluated the cation distribution in inverse spinel NiCo2O4 films that were epitaxially grown by pulsed laser deposition. Our results reveal that oxygen partial pressure during growth PO2 is a key parameter determining cation distribution in the films, with a larger PO2 leading to an increase in the Ni concentration occupying the octahedral (Oh) sites. We further show that the PO2-dependent Oh-site Ni concentration impacts the magnetic properties of the films: Films having the cation distribution close to the stoichiometric exhibit ferrimagnetism with a transition temperature higher than 400 K and enhanced perpendicular magnetic anisotropy. On the other hand, the reductions in the Oh-site Ni concentration leads to the deterioration of the ferrimagnetic properties such as magnetization, transition temperature, and anisotropy energy. Our study demonstrates that the ferrimagnetic properties and the anisotropy can be tuned through the cation distribution, which would provide an additional degree of freedom in designing spintronic devices based on spinel oxides including NiCo2O4.