Epitaxial growth of Mn–Co–Ni–O thin films and thickness effects on the electrical properties

Abstract Mn 1.56 Co 0.96 Ni 0.48 O 4 (MCN) thin films were grown on thermally oxidized Si(1 0 0) substrates using laser molecular beam epitaxy technique. The X-ray diffraction and high-resolution transmission electron microscopy analyses indicated an epitaxial structure with [1 0 0] growth direction and a lattice parameter of 8.28 A. The resistivity-temperature relationships of the epitaxial MCN thin films exhibited negative temperature coefficient thermistor characteristics, and the electron conduction mechanism was found to be nearest-neighbor hopping. Interestingly, the room temperature resistivity ρ 25 , the characteristic temperature T 0 , the activation energy E a , and the temperature coefficient of resistance α T were all highly dependent on the film thickness t , and as t increased all of them decreased. An approximately linear relation was further revealed between ρ 25 and 1/ t 2 , which could be approximately expressed as ρ 25 ( t )=211.7+119.1×10 4 / t 2 ( t in nm; ρ 25 in Ω cm). The successful growth of epitaxial MCN thin films opens a door for studying the effects of thickness on the electrical properties of MCN thin films, and may consequently provide an alternative approach for controlling the properties.