Greigite and Spinorbitronics*

Greigite(Fe$_{3}$S$_{4})$ and magnetite(Fe$_{3}$O$_{4})$ are isoelectronic and isostructural ferrimagnets. In biology, the motility of magnetotactic bacteria is based on any or both of them. Not much work is known on greigite. Unlike half-metallic magnetite, greigite is a normal metal. Although the constituent elements are light, the complex Fermi-surface of greigite is remarkably sensitive to relativistic effects. The existence of several Fermi-surface sheets is dependent on the direction of the magnetization. This implies spintronics based on a homogeneous material rather than a device. Since this effect is intrinsically relativistic, spin-contamination is irrelevant here.