期刊
JOURNAL OF PHYSICS AND CHEMISTRY OF SOLIDS
卷 160, 期 -, 页码 -出版社
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.jpcs.2021.110321
关键词
Sensitive metallic behavior; Transport properties; Epitaxial film; NiCo2O4; Film thickness
资金
- National Natural Science Foundation of China [51971087, 51901067]
- Natural Science Foundation of Hebei Province [A2018205144, A2017210070, E2019205234]
The metallic behavior in NiCo2O4 films is influenced by temperature and film thickness, with a 31-nm thick film showing the widest temperature window for metallic behavior. Films thinner than 31 nm exhibit quasi-two-dimensional behavior, affected by substrate clamping, while films thicker than 31 nm are three-dimensional with long-range structural order.
The transition metal oxide NiCo2O4 has aroused extensive research interest due to its metallic conductivity, but the precise nature of the conductivity remains elusive. In this study, the dependence of the metallic behavior in NiCo2O4 epitaxial films on temperature and film thickness are investigated for film thicknesses in the range of 7-155 nm. Our results show that a subtle lattice distortion caused by the substrate is necessary for metallic behavior in NiCo2O4 films. The widest temperature window for the metallic behavior is obtained for a 31-nm thick NiCo2O4 film. The NiCo2O4 films thinner than 31 nm are quasi-two-dimensional, and are affected by substrate clamping. In these films, conduction is constrained by electron-electron and electron-magnon scattering. However, NiCo2O4 films thicker than 31 nm are three-dimensional, exhibiting long-range structural order, with electrical transport constrained mainly by electron-phonon scattering, as well as electron-electron and electron-magnon scattering. Our study demonstrates that the metallic behavior in NiCo2O4 films can be tuned using the film thickness, which is of great significance for application of NiCo2O4 in development of alternative ferroelectric metal electrodes in magnetic tunnel junctions.
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