Short-range magnetic order and electrical behavior in epitaxial NiCo2O4 thin films

As an electrode material with reported ferrimagnetic properties, the NiCo2O4 film exhibits critical electrical transport properties under a magnetic field as well as a magnetic microstructure. In this study, epitaxial NiCo2O4 films were prepared on LaAlO3 (100) substrates, and the effects of growth temperature on the magnetic and electrical transport properties of the films were investigated. Negative magnetoresistance was observed in the films due to the local spin effect. The NiCo2O4 films demonstrated a topological Hall effect, which is closely related to short-range magnetic order and a noncoplanar magnetic structure in NiCo2O4 films. The results indicate that there are two types of spin frustration in the NiCo2O4 structure. One is a diamond lattice composed of tetrahedral site cations, while the other is a triangular lattice structure formed by the edge-shared octahedral cations. For the NiCo2O4 (100) films, the sign of the ordinary Hall coefficient reverses by decreasing the measurement temperature, indicating that the carrier type changes from p to n.