Iron nitride permanent magnet and technique for forming iron nitride permanent magnet

1. A bulk permanent magnetic material comprising:

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 comprising Fe 8 N is magnetically coupled to the Fe 16 N 2 phase domains via exchange spring coupling.

2. The bulk permanent magnetic material of claim 1 , comprising between about 5 volume percent and about 20 volume percent Fe 16 N 2 phase domains.

3. The bulk permanent magnetic material of claim 1 , wherein the Fe 16 N 2 phase domains are distributed throughout a volume of the bulk permanent magnetic material.

4. The bulk permanent magnetic material of claim 1 , wherein the plurality of nonmagnetic atoms or molecules comprises an element or compound selected from the group consisting of Al, Cu, Ti, Mn, Zr, Ta, B, C, Ni, Ru, SiO 2 , Al 2 O 3 , or combinations thereof.

5. The bulk permanent magnetic material of claim 1 , wherein the soft magnetic material further comprises an element or compound selected from the group consisting of Fe 4 N, Fe, and combinations thereof.

6. The bulk permanent magnetic material of claim 1 , wherein the bulk permanent magnetic material comprises a plurality of workpieces of iron nitride, each workpiece of iron nitride including the soft magnetic material and between about 5 volume percent and about 40 volume percent Fe 16 N 2 phase domains.

7. The bulk permanent magnetic material of claim 1 , wherein a smallest dimension of the bulk permanent magnetic material is greater than about 100 nanometers.

8. The bulk permanent magnetic material of claim 7 , wherein the smallest dimension is greater than about 100 micrometers.

9. The bulk permanent magnetic material of claim 1 , wherein the magnetic material has an energy product of greater than about 10 MGOe.

10. The bulk permanent magnetic material of claim 9 , wherein the magnetic material has an energy product of greater than about 30 MGOe.

11. The bulk permanent magnetic material of claim 1 , wherein the bulk permanent magnetic material is naturally crystallographically coherent.

12. The bulk permanent magnetic material of claim 1 , wherein the bulk permanent magnet does not include a powder phase.

13. The bulk permanent magnetic material of claim 1 , wherein the domain wall pinning sites have sizes ranging from several nanometers to several hundred nanometers.

14. A method comprising:

forming a plurality of workpieces of iron nitride material, each of the plurality of workpieces including between about 5 volume percent and about 40 volume percent of Fe 16 N 2 phase domains and a soft magnetic material comprising Fe 8 N;

introducing a plurality of nonmagnetic atoms or molecules between the plurality of workpieces or within at least one of the plurality of workpieces of iron nitride material; and

joining the plurality of workpieces of iron nitride to form a bulk permanent magnetic material including iron nitride with between about 5 volume percent and about 40 volume percent of Fe 16 N 2 phase domains, the plurality of nonmagnetic atoms or molecules forming domain wall pinning sites, and a balance soft magnetic material comprising Fe 8 N, wherein at least some of the soft magnetic material is magnetically coupled to the Fe 16 N 2 phase domains via exchange spring coupling.

15. The method of claim 14 , wherein forming the plurality of workpieces of iron nitride material comprises:

implanting N+ ions in a textured iron workpiece using ion implantation to form a textured iron nitride workpiece; and

post-annealing the textured iron nitride workpiece to form Fe 16 N 2 phase domains within the textured iron nitride workpiece.

16. The method of claim 15 , further comprising forming the textured iron workpiece using fast belt casting.

17. The method of claim 15 , wherein implanting N+ ions in the textured workpiece using ion implantation to form the textured iron nitride workpiece comprises:

accelerating N+ ions to an energy of less than about 180 kiloelectron volts.

18. The method of claim 15 , wherein implanting N+ ions in the textured workpiece using ion implantation to form the textured iron nitride workpiece comprises:

providing N+ ions at a fluence of between about 2×10 16 /cm 2 and about 1×10 17 /cm 2 .

19. The method of claim 15 , wherein implanting N+ ions in the textured workpiece using ion implantation to form the textured iron nitride workpiece comprises:

providing sufficient N+ ions to form an average concentration of nitrogen in the textured iron nitride workpiece between about 8 atomic percent and about 15 atomic percent.

20. The method of claim 14 , wherein forming the plurality of workpieces of iron nitride material comprises:

mixing a nitrogen source in molten iron;

fast belt casting the molten iron to form a textured iron nitride workpiece; and

post-annealing the textured iron nitride workpiece to form Fe 16 N 2 phase domains within the textured iron nitride workpiece.

21. The method of claim 20 , wherein mixing nitrogen in molten iron comprises:

mixing the nitrogen source in molten iron to result in a concentration of nitrogen atoms in the molten iron between about 8 atomic percent and about 15 atomic percent.

22. The method of claim 20 , wherein the nitrogen source comprises at least one of ammonia, ammonium azide, or urea.

23. The method of claim 14 , wherein the textured iron nitride workpiece includes a (100) or a (110) crystal structure.

24. The method of claim 14 , wherein the textured iron nitride workpiece defines a dimension between about 1 micrometer and about 10 millimeters.

25. The method of claim 14 , wherein post-annealing the textured iron nitride workpiece to form Fe 16 N 2 phase domains within the textured iron nitride workpiece comprises:

exerting a strain on the textured iron nitride workpiece between about 0.1% and about 7%; and

while exerting the strain on the textured iron nitride workpiece, heating the textured iron nitride workpiece to a temperature between about 120° C. and about 250° C. for at least about 5 hours.

26. The method of claim 25 , wherein heating the textured iron nitride workpiece to a temperature between about 120° C. and about 250° C. for at least about 5 hours comprises:

heating the textured iron nitride workpiece to a temperature of about 150° C. for between about 20 hours and about 40 hours.

27. The method of claim 15 , wherein post-annealing the textured iron nitride workpiece to form Fe 16 N 2 phase domains within the textured iron nitride workpiece comprises:

forming between about 5 volume percent and about 40 volume percent of Fe 16 N 2 phase domains within the textured iron nitride workpiece.

28. The method of claim 15 , wherein post-annealing the textured iron nitride workpiece to form Fe 16 N 2 phase domains within the textured iron nitride workpiece comprises:

forming between about 10 volume percent and about 17 volume percent of Fe 16 N 2 phase domains within the textured iron nitride workpiece.

29. The method of claim 15 , wherein post-annealing the textured iron nitride workpiece to form Fe 16 N 2 phase domains within the textured iron nitride workpiece comprises:

forming Fe 16 N 2 distributed throughout a volume of the textured iron nitride workpiece.

30. The method of claim 14 , wherein introducing the plurality of nonmagnetic material atoms or molecules between the plurality of workpieces or within at least one of the plurality of workpieces of iron nitride material comprises:

implanting nonmagnetic ions within at least one of the plurality of workpieces of iron nitride material using ion implantation.

31. The method of claim 14 , wherein introducing the plurality of nonmagnetic material atoms or molecules between the plurality of workpieces or within at least one of the plurality of workpieces of iron nitride material comprises:

implanting nonmagnetic molecules within at least one of the plurality of workpieces of iron nitride material using cluster implantation.

32. The method of claim 14 , wherein introducing the plurality of nonmagnetic material atoms or molecules between the plurality of workpieces or within at least one of the plurality of workpieces of iron nitride material comprises:

introducing workpieces of the plurality of nonmagnetic material atoms or molecules between a first workpiece and a second workpiece of the plurality of workpieces of iron nitride material.

33. The method of claim 14 , wherein introducing the plurality of nonmagnetic material atoms or molecules between the plurality of workpieces or within at least one of the plurality of workpieces of iron nitride material comprises:

introducing a powder comprising at least one of iron or nonmagnetic material between a first workpiece and a second workpiece of the plurality of workpieces of iron nitride material.

34. The method of claim 14 , wherein the plurality of nonmagnetic material atoms or molecules are selected from the group consisting of Al, Cu, Ti, Mn, Zr, Ta, B, C, Ni, Ru, SiO 2 , Al 2 O 3 , or combinations thereof.

35. The method of claim 14 , wherein joining the plurality of workpieces of iron nitride to form a bulk magnet including iron nitride with between about 5 volume percent and about 40 volume percent of Fe 16 N 2 phase domains comprises:

heating the plurality of workpieces of iron nitride to a temperature below about 250° C. for at least about 5 hours while applying a pressure of between about 0.2 gigapascal and about 10 gigapascals to the plurality of workpieces of iron nitride.