ferrous nitride is an iron-nitrogen alloy with properties comparable to rare-earth magnets. It is a very hard, brittle material that can be used in magnetic materials such as permanent magnets.
The nitride has a crystal structure similar to iron, a body-centered cubic (BCC) or face-centered cubic (FCC), with eight atoms centered on the corners of a perfect cube and one atom at the center of each face. Its high ferromagnetic moment comes from the axial asymmetry of each crystal, and the electronic structure of the elements in the alloy.
Creating magnets from this material requires a complex process that doesn’t lend itself well to commercial production. But scientists have found a way to make the iron-nitrogen alloy using a technique that is common in semiconductor manufacturing, where ions are accelerated by an electric field and slammed into substrates.
Ion implantation produces a distorted, hard-magnetic foil that can be used to create a magnet. To do this, a pure iron foil 500 nm thick is mounted on a silicon substrate and bombarded with atomic nitrogen ions.
After a series of annealing steps, the implanted nitrogen activates and traps it within the foil’s crystal structure, producing the distortion necessary to produce hard magnetic behavior. The nitrided foil can then be stacked and bound into a single structure to form practical magnets.
While there’s a long way to go between these experiments and industrial applications, the nitrided foil is already being used to develop iron-nitrogen permanent magnets in the lab at the University of Minnesota. These magnets are being used to control the position of microchips in computer chips and in magnetic sensors for aerospace applications.
