Perpendicular Magnetic Anisotropic NiCo2O4 Epitaxial Films with Tunable Coercivity

Ferrimagnetic ${\mathrm{Ni}\mathrm{Co}}_{2}{\mathrm{O}}_{4}$ (NCO) films with perpendicular magnetic anisotropy, 12.5 nm in thickness, are epitaxially deposited on (001) ${\mathrm{Mg}\mathrm{Al}}_{2}{\mathrm{O}}_{4}$ single-crystalline substrates by pulsed laser deposition. It is observed that the coercive field of the NCO films can be tuned systematically by about 20 times, while keeping the large perpendicular magnetic anisotropy, through simply increasing the deposition temperature from 250 to 350 \ifmmode^\circ\else\textdegree\fi{}C. The increase of resistivity and the increase of low-temperature metal-to-insulator transition temperature suggests increased concentration of defects in NCO films deposited at elevated temperatures. The magnetic and transport characteristics are discussed based on a systematic change in cation valence and coordination in NCO films, as revealed by x-ray photoelectron emission and x-ray absorption spectroscopy measurements. The perpendicular magnetic anisotropy with tunable coercivity makes NCO films promising for multifunctional applications.