Since 1970 we have known that bacteria exist in nature which naturally produce nano-magnets. These bacteria, can point and move themselves along magnetic fields and are called magnetotactic. They have an organelle, the magnetosome, which contains a nano-magnet. This sometimes consists of magnetite although may also consist of greigite, another magnetic material.
These magnetotactic bacteria live in water or in sediments often formed from layers made up of different chemical compositions. Magnetotaxis enables the bacteria to point themselves towards areas with more nutrients.