Spin Polarized Electron Emission from Magnetite Half-metals Determined by First-principles Calculations

Magnetite is a mineral and one of the main iron ores. With the chemical formula Fe₃O₄, 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 using first principles or ab initio calculations based on density functional theory. With a +U calculation, most of the surfaces with different terminations show half-metallic, different from those predicted by a without +U calculation. It is proposed that the magnetite as a half-metal can possibly be used as a spin-polarized electron source. The spin polarized electrons can be obtained via the field emission process as described by the Fowler–Nordheim equation. From the first principles calculations, the surfaces suitable for spin polarized emission are found.