Anomalous Hall effect and spin reorientation in (110)-oriented NiCo2O4 epitaxial films

Abstract

Compared to high-symmetry (001)-oriented films, the low-symmetry and anisotropically strained (110)-oriented NiCo2O4 films provide an essential platform for investigating the origins of magnetic anisotropy and the mechanisms underlying the anomalous Hall effect. High-quality epitaxial NiCo2O4 thin films with (110) orientation were grown on MgAl2O4 substrates via off-axis radio frequency magnetron sputtering. The NiCo2O4 films thicker than 2.2 nm exhibit metallic conduction above ∼44 ± 1 K, whereas the 2.2 nm ultrathin films display semiconducting behavior. Robust in-plane ferrimagnetic ordering for the 8.6 nm NCO film is characterized by a saturation magnetization of 2.02 μB/f.u. at 10 K and a Curie temperature of ∼380 K, with field-induced spin reorientation occurring around 6 kOe at 10 K. The anomalous Hall effect exhibits a nonmonotonic temperature dependence, with a sign reversal occurring at 100 K for 8.6 nm films and at 160 K for 6.5 nm films. Notably, resistance fluctuations near the spin reorientation field are observed at low temperatures, attributed to pronounced variations in magnetic domain structures. The scaling relation reveals competition between intrinsic Berry phase contributions and extrinsic scattering mechanisms. These findings underscore the critical role of crystal orientation and strain engineering in tuning the multifunctional properties of NiCo2O4, offering avenues for the design of spintronic devices based on the anomalous Hall effect and magnetic anisotropy.