Electrical transport and optical band gap of NiFe$_\textrm{2}$O$_\textrm{x}$ thin films

TL;DR

This study investigates how varying oxygen content in NiFe₂Oₓ thin films affects their electrical and optical properties, revealing controllable transport mechanisms and band gaps suitable for spintronic applications.

Contribution

It demonstrates the fabrication of NiFe₂Oₓ films with tunable properties through oxygen partial pressure control, linking structural, electrical, and optical characteristics.

Findings

Lower oxidation increases electrical conductivity and reduces band gap.

Films exhibit mixed-type semiconducting behavior.

Transport mechanisms vary with temperature and oxygen content.

Abstract

We fabricated NiFe$_\textrm{2}$O$_\textrm{x}$ thin films on MgAl$_2$O$_4$(001) substrates by reactive dc magnetron co-sputtering varying the oxygen partial pressure during deposition. The fabrication of a variable material with oxygen deficiency leads to controllable electrical and optical properties which would be beneficial for the investigations of the transport phenomena and would, therefore, promote the use of such materials in spintronic and spin caloritronic applications. We used several characterization techniques in order to investigate the film properties, focusing on their structural, magnetic, electrical, and optical properties. From the electrical resistivity measurements we obtained the conduction mechanisms that govern the systems in high and low temperature regimes, extracting low thermal activation energies which unveil extrinsic transport mechanisms. The thermal activation energy decreases in the less oxidized samples revealing the pronounced contribution of a large amount of electronic states localized in the band gap to the electrical conductivity. Hall effect measurements showed the mixed-type semiconducting character of our films. The optical band gaps were determined via ultraviolet-visible spectroscopy. They follow a similar trend as the thermal activation energy, with lower band gap values in the less oxidized samples.