Peculiar thickness dependence of perpendicular magnetic anisotropy in epitaxial NiCo2O4 spinel films

We reported a peculiar thickness dependence of perpendicular magnetic anisotropy (PMA), stronger in thinner films, in spinel NiCo2O4 (NCO) films deposited epitaxially on MgAl2O4 (001) single crystalline substrates. The effective PMA field is about 3 T in 23.0 nm-thick films but increases dramatically to about 7 T in 4.5 nm-thick films. X-ray absorption spectra reveal an inhomogeneous distribution of Co2+ cations along the film's normal with more Co2+ adjacent to the film/substrate interface. X-ray linear dichroism spectra reveal that the PMA in NCO films is associated with electrons occupying the x(2)-y(2) orbital of Co cations at the tetrahedral sites. This work demonstrates the potential of ultrathin NCO films in all-oxide spintronic devices.

Automated summary

We reported an unusual thickness dependence of perpendicular magnetic anisotropy (PMA) in epitaxially deposited spinel NiCo2O4 (NCO) films on MgAl2O4 (001) single crystalline substrates, which is stronger in thinner films. The effective PMA field increases from about 3 T in 23.0 nm-thick films to about 7 T in 4.5 nm-thick films. X-ray absorption spectra reveal an inhomogeneous distribution of Co2+ cations along the film's normal, with a higher concentration near the film/substrate interface. X-ray linear dichroism spectra indicate that the PMA in NCO films is associated with the x(2)-y(2) orbital of Co cations at the tetrahedral sites. This work demonstrates the potential of ultrathin NCO films in all-oxide spintronic devices.