Epitaxial Films*

The room temperature ferrimagnetic spinel structured NiCo₂O₄ (NCO) has garnered interest due to its potential applications in high-capacity supercapacitors. Additional applications in spintronics necessitate studies on its magnetic behavior, which comes about from the magnetic Co tetrahedral and mixed Ni/Co octahedral sites.

We present SQUID measurements on pulsed laser deposited NCO thin films. Measurements show NCO grown on (001)-oriented MgAl₂O₄ (MAO) single-crystal substrates display an unconventional out-of-plane magnetic easy axis, overcoming shape anisotropy effects of the thin film. NCO/MAO(110) and NCO/MAO(111) films show in-plane easy axes defined by the crystallographic orientation of the substrate. The anisotropy comes about due to distortion of the local environments around the magnetic cations. Observations are explained using single-ion anisotropy and crystal field theory considerations. Research presented opens possibilities for dynamic control of magnetism based on applied strain.