The disclosure describes techniques for forming nanoparticles including Fe.sub.16N.sub.2 phase. In some examples, the nanoparticles may be formed by first forming nanoparticles including iron, nitrogen, and at least one of carbon or boron. The carbon or boron may be incorporated into the nanoparticles such that the iron, nitrogen, and at least one of carbon or boron are mixed. Alternatively, the at least one of carbon or boron may be coated on a surface of a nanoparticle including iron and nitrogen. The nano particle including iron, nitrogen, and at least one of carbon or boron then may be annealed to form at least one phase domain including at least one of Fe.sub.16N.sub.2, Fe.sub.16(NB).sub.2, Fe.sub.16(NC).sub.2, or Fe.sub.16(NCB).sub.2.

A hard magnetic material formed of material powders made of a RFeN compound containing a light rare earth element as R, or material powders made of a FeN compound is used as material powders. There is formed a compact in which a density of the hard magnetic material powders differs between an outer face side portion and an inside portion of the compact such that a rate of progress of powder bonding due to microwave heating is higher in the inside portion of the compact than in the outer face side portion of the compact when an outer face of the compact is irradiated with microwaves. Then, the outer face of the compact is irradiated with the microwaves to cause the microwave heating, thereby bonding the hard magnetic material powders by oxide films which are formed on the hard magnetic material powders.

A method may include annealing a material including iron and nitrogen in the presence of an applied magnetic field to form at least one Fe.sub.16N.sub.2 phase domain. The applied magnetic field may have a strength of at least about 0.2 Tesla (T).

Example nanoparticles may include an iron-based core, and a shell. The shell may include a non-magnetic, anti-ferromagnetic, or ferrimagnetic material. Example alloy compositions may include an iron-based grain, and a grain boundary. The grain boundary may include a non-magnetic, anti-ferromagnetic, or ferrimagnetic material. Example techniques for forming iron-based core-shell nanoparticles may include depositing a shell on an iron-based core. The depositing may include immersing the iron-based core in a salt composition for a predetermined period of time. The depositing may include milling the iron-based core with a salt composition for a predetermined period of time. Example techniques for treating a composition comprising core-shell nanoparticles may include nitriding the composition.

The disclosure describes techniques for forming nanoparticles including Fe.sub.16N.sub.2 phase. In some examples, the nanoparticles may be formed by first forming nanoparticles including iron, nitrogen, and at least one of carbon or boron. The carbon or boron may be incorporated into the nanoparticles such that the iron, nitrogen, and at least one of carbon or boron are mixed. Alternatively, the at least one of carbon or boron may be coated on a surface of a nanoparticle including iron and nitrogen. The nanoparticle including iron, nitrogen, and at least one of carbon or boron then may be annealed to form at least one phase domain including at least one of Fe.sub.16N.sub.2, Fe.sub.16(NB).sub.2, Fe.sub.16(NC).sub.2, or Fe.sub.16(NCB).sub.2.