Investigation of Electrically Driven Phase Transition in Magnetite Thin Films*

Magnetite, Fe$_{3}$O$_{4}$, is an example of strongly electronically correlated system. It undergoes so called Verwey transition at T$_{V}\sim $122 K accompanied both by structural distortion and drastic decrease in electrical conductivity, i.e. metal-insulator transition. Recently, we discovered a new electrically driven phase transition in magnetite nanoparticles and thin films. We observed that a low-temperature (T below T$_{V})$ insulating state is broken upon applying an electric field, resulting in a sharp transition to the state with much higher conductivity. We report on further electrical characterization of this newly discovered state. There is a question whether this state is the same as high-temperature phase above T$_{V}$ or this is a new state of magnetite. In standard two-terminal measurement dominant contribution of contact resistance impedes intrinsic electrical properties. Thus, four-terminal configuration is necessary. Electrical and magnetoresistance properties are measured in challenging four-terminal geometry at nanoscale.