Influence of growth temperature on the microstructure and electrical transport properties of epitaxial NiCo2O4 thin films

In the work reported here, NiCo2O4 films were grown epitaxially on LaAlO3 (111) substrates at temperatures between room temperature and 700 °C. The effects of the substrate temperature (Tsub) on the structural, electrical and magnetic properties and on the Hall effect of the film were investigated. Tsub has a great influence on the cation disorder. High Tsub makes substitution of Ni (Oh) for Co (Td) easier, and changes the relative Ni3+/Co3+ concentration. The film grown at 400 °C had a relatively larger concentration of Ni3+, which lowers the resistivity and enhances the ferrimagnetism of the NiCo2O4 film. In addition, a sign change in the Hall coefficient from negative to positive was observed with increasing measurement temperature for each of the samples grown at different substrate temperatures.