Absence of Metallic Behavior in Epitaxial NiCo2O4 Thin Films: Role of Microstructural Disorder

Abstract

Despite the low resistivity (~ 1 mohm cm), the metallic electrical transport has not been commonly observed in the inverse spinel NiCo2O4, except in certain epitaxial thin films. Previous studies have stressed the effect of valence mixing and degree of spinel inversion on the electric conduction of NiCo2O4 films. In this work, we have studied the effect of microstructure by comparing the NiCo2O4 epitaxial films grown on MgAl2O4 (111) and on Al2O3 (0001) substrates. Although the optimal growth condition and the magnetic properties are similar for the NiCo2O4/MgAl2O4 and the NiCo2O4/Al2O3, they show metallic and semiconducting electrical transport respectively. Despite similar temperature and field dependence of magnetization, the NiCo2O4/Al2O3 show much larger magnetoresistance at low temperature. Post-growth annealing decreases the resistivity of NiCo2O4/Al2O3, but the annealed films are still semiconducting. The correlation between the structural correlation length and the resistivity suggests that the microstructural disorder, generated by the dramatic mismatch between the NiCo2O4 and Al2O3 crystal structures, may be the origin of the absence of the metallic electrical transport in NiCo2O4. These results reveal microstructural disorder as another key factor in controlling the electrical transport of NiCo2O4, with potentially large magnetoresistance for spintronics application.

References in corpus (3)

• Charge order, dynamics, and magneto-structural transition in multiferroic LuFe${}_2$O${}_4$
• Epitaxial Zn(x)Fe(3-x)O(4) Thin Films: A Spintronic Material with Tunable Electrical and Magnetic Properties
• Kinetics and Intermediate Phases in Epitaxial Growth of Fe3O4 Films from Deposition and Thermal Reduction

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• Tuning the Néel temperature in an antiferromagnet: the case of NixCo1-xO microstructures
• Anomalous Hall Effect and Perpendicular Magnetic Anisotropy in Ultrathin Ferrimagnetic NiCo${}_2$O${}_4$ Films
• Spin reorientation in tetragonally distorted spinel oxide NiCo${}_2$O${}_4$ epitaxial films
• Interfacial and Surface Magnetism in Epitaxial NiCo2O4(001)/MgAl2O4 Films
• Persistent Ionic Photo-responses and Frank-Condon Mechanism in Proton-transfer Ferroelectrics
• Intrinsic Exchange Bias from Interfacial Reconstruction in an Epitaxial NixCoyFe3-x-yO4(111)/α-Al2O3(0001) Thin Film Family