Contact effects on transport in magnetite, an archetypal correlated transition metal oxide

TL;DR

This study investigates how different metal contacts affect the electrical transport properties of magnetite (Fe3O4), revealing contact resistance trends related to work function and insights into the insulator-metal transition in this correlated oxide.

Contribution

It provides the first systematic analysis of contact effects on Fe3O4's transport properties, linking contact resistance to work function and the insulator-metal transition mechanism.

Findings

Contact resistance decreases with higher metal work function.

Contact resistance is proportional to Fe3O4 resistivity.

Contact resistance jumps at the insulator-metal transition are influenced by electrode work function.

Abstract

Multiterminal measurements have typically been employed to examine electronic properties of strongly correlated electronic materials such as transition metal oxides without the influence of contact effects. In contrast, in this work we investigate the interface properties of Fe$_3$O$_4$ with different metals, with the contact effects providing a window on the physics at work in the correlated oxide. Contact resistances are determined by means of four-terminal electrical measurements as a function of source voltage and temperature. Contact resistances vary systematically with the work function of the electrode metal, $\phi(M)$, $M=$Cu, Au and Pt, with higher work function yielding lower contact resistance. This trend and the observation that contact resistances are directly proportional to the Fe$_3$O$_4$ resistivity are consistent with modeling the oxide as an effective $p$-type semiconductor with hopping transport. The jumps in contact resistance values at the bias-driven insulator-metal transition have a similar trend with $\phi$($M$), consistent with the transition mechanism of charge gap closure by electric field.