We have grown epitaxial thin films of spinel NiCo2O4 on single crystalline MgAl2O4 (001) substrates by pulsed laser deposition. Magnetization measurement revealed hysteresis loops consistent with the reported ferrimagnetic order. The electrical transport exhibits a metallic behavior with the lowest resistivity of 0.8 mΩ cm and a metal insulator transition around the Néel temperature. The systematic variation in the properties of the films grown at different growth temperatures indicates a close relationship between the magnetic order and electrical transport.
Epitaxial thin films of spinel NiCo2O4 (NCO) grown on MgAl2O4 (001) substrates are reported to exhibit dramatic changes in the magnetic and transport properties with deposition temperature. While films grown at lower temperatures (<450°C) are ferrimagnetic with metallic characteristics, those grown at higher temperatures are non-magnetic and insulating. Detailed polarized Raman spectroscopy studies indicate that the higher temperature films have close to the ideal inverse spinel cation distribution, Co3+[Ni2+Co3+]O42−, whereas those deposited at lower temperature are characterized by mixed cation/charge distribution at both the tetragonal (A) and octahedral (B) sites. Additionally, temperature-dependent Raman studies demonstrate that, unlike bulk polycrystalline samples, all the NCO films are robust against thermal treatment with full reversibility after annealing at 600°C in oxygen and air. However, partial decomposition is observed after annealing in vacuum.
We present the thickness dependent structural, magnetic, and transport properties of transparent conducting spinel NiCo2O4 thin films on MgAl2O4 (001) substrates. The structural examination of the films reveals that the epitaxial stain is independent of the films' thickness. Electric and magnetic measurements show that the films are metallic with p-type conduction and ferrimagnetic down to 2 unit cells with an enhanced coercive field in the films thinner than 30 unit cells. The low-temperature resistivity data indicate that the observed resistivity minimum results from the disorder-induced quantum interference effects. Our results demonstrate that NiCo2O4 may provide an alternative magnetic conducting medium for spintronics devices.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.