Iron nitride permanent magnet and technique for forming iron nitride permanent magnet
A bulk permanent magnetic material may include between about 5 volume percent and about 40 volume percent Fe 16 N 2 phase domains, a plurality of nonmagnetic atoms or molecules forming domain wall pinning sites, and a balance soft magnetic material, wherein at least some of the soft magnetic material is magnetically coupled to the Fe 16 N 2 phase domains via exchange spring coupling. In some examples, a bulk permanent magnetic material may be formed by implanting N+ ions in an iron workpiece using ion implantation to form an iron nitride workpiece, pre-annealing the iron nitride workpiece to attach the iron nitride workpiece to a substrate, and post-annealing the iron nitride workpiece to form Fe 16 N 2 phase domains within the iron nitride workpiece.
1. A bulk permanent magnetic material comprising:
Fe 16 N 2 phase domains, wherein the Fe 16 N 2 phase domains form hard magnetic domains;
a plurality of nonmagnetic atoms or molecules forming domain wall pinning sites; and
soft magnetic material comprising Fe 8 N, wherein at least some of the soft magnetic material is magnetically coupled to the hard magnetic Fe 16 N 2 phase domains.
2. The bulk permanent magnetic material of claim 1 , further comprising:
dopant elements to form domain wall pinning sites within the magnetic material.
3. The bulk permanent magnetic material of claim 2 , wherein the dopant elements comprises at least one of cobalt (Co), titanium (Ti), copper (Cu) and zinc (Zn).
4. The bulk permanent magnetic material of claim 1 , wherein crystallographic textures of the Fe 16 N 2 and the Fe 8 N are coherent.
5. The bulk permanent magnetic material of claim 1 , wherein the Fe 16 N 2 phase domains are chemically ordered.
6. The bulk permanent magnetic material of claim 5 , wherein the Fe 8 N comprises α′ phase Fe 8 N, wherein the Fe 8 N is a chemically disordered counterpart of the chemically-ordered Fe 16 N 2 phase domains.
7. A method of producing the bulk permanent magnetic material according to claim 1 , comprising
positioning an iron workpiece on a surface of a substrate;
carrying out ion implantation to implant N+ ions in an iron workpiece; and
subsequently performing two annealing processes, pre-annealing and post-annealing,
wherein the pre-annealing is carried out to attach the iron nitride workpiece to the substrate; and
wherein the post-annealing is carried out at a temperature lower than a pre-annealing temperature.
8. The method of claim 7 , further comprising:
facilitating transformation of a crystalline structure of at least some of crystals in the iron workpiece from body centered cubic (bcc) iron to body centered tetragonal (bct) iron nitride during the post-annealing; and
forming Fe 16 N 2 and Fe 8 N phases.
9. The method of claim 7 , wherein the pre-annealing is carried out at a temperature in a range of from 450° C. to 550° C.
10. The method of claim 7 , further comprising:
applying an external force between about 0.2 gigapascals (GPa) and about 10 GPa between the iron workpiece and the substrate during the pre-annealing.
11. The method of claim 7 , wherein an atmosphere in which the pre-annealing step is performed comprises at least one of nitrogen, argon, and hydrogen.
12. The method of claim 7 , wherein the temperature for the post-annealing is below 250° C.
13. The method of claim 8 , further comprising:
combining multiple workpieces of the Fe 16 N 2 +Fe 8 N, and
pressing the combined multiple workpieces together to form the bulk permanent magnetic material.
14. The method of claim 13 , further comprising:
introducing magnetically soft or nonmagnetic dopant materials.
15. The method of claim 7 , wherein the substrate comprises at least one of silicon and gallium arsenide (GaAs).