Local work functions of magnetite under electric fields based on first principle calculations

Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe
₃
O
₄
, it is one of the oxides of iron. Magnetite is the earliest discovered magnet, around 1500 B.C. It crystallizes in the inverse cubic spinel structure (Fd3m) above the so-called Verwey transition temperature which is about 120 K. In this work, we study the electronic properties of magnetite (100), (110), and (111) surfaces under external electric fields using first principles or ab initio calculations based on density functional theory. With an electric field applied, the effective work function changes under different field strength. By calculating the local work function, we can know the distribution of work function on a certain surface. The effective work functions of magnetite Fe
₃
O
₄
on different surfaces have been determined. The local work function has been found to have the correspondences with the atoms' positions and charge densities. In addition, the deviation in local work function (Δφ) increases proportionally to an increasing electric field up to 0.2 V/A. It is proposed that the magnetite as a half-metal can possibly be used as a spin-polarized electron source.