Iron-based composition for magnetocaloric effect (MCE) applications and method of making a single crystal

1. A method of making a single crystal, the method comprising:

heating a material comprising magnetic anisotropy to a temperature T sufficient to form a melt of the material;

applying a magnetic field of at least about 1 Tesla to the melt at the temperature T, where a magnetic free energy difference ΔG m between different crystallographic axes of the material is greater than a thermal energy kT;

while applying the magnetic field, cooling the melt at a rate of about 30° C./min or higher;

during the cooling, applying an alternating magnetic field at a frequency of from about 10 kHz to about 300 kHz; and

solidifying the melt to form a single crystal of the material.

2. The method of claim 1 , wherein the magnetic field is at least about 5 Tesla.

3. The method of claim 1 , wherein the magnetic anisotropy includes at least one member selected from the group consisting of: magnetocrystalline anisotropy and magnetic shape anisotropy.

4. The method of claim 1 , wherein the melt is contained in a crucible, and the magnetic field is applied in a direction parallel to a longitudinal axis of the crucible.

5. The method of claim 1 , wherein the solidification occurs while the magnetic field is applied.

6. The method of claim 1 , wherein the rate of cooling is about 100° C./min or higher.

7. The method of claim 1 , wherein cooling the melt comprises extracting heat from the melt in a plurality of directions.

8. The method of claim 7 , wherein the plurality of directions extend over an angular range of greater than 180°.

9. The method of claim 1 , wherein cooling the melt comprises flowing a thermally conductive gas over the melt.

10. The method of claim 1 , wherein, during the solidification of the melt to form the single crystal of the material, one of the crystallographic axes of the material is aligned parallel to a direction of the magnetic field.

11. The method of claim 1 , wherein the material is ferromagnetic at room temperature.

12. The method of claim 1 , wherein the material is paramagnetic at room temperature.

13. The method of claim 1 , wherein the single crystal has a size of at least about 15 cm 3 .

14. A method of making a single crystal, the method comprising:

heating a material comprising magnetic anisotropy to a temperature T sufficient to form a melt of the material;

applying a magnetic field of at least about 1 Tesla to the melt at the temperature T, where a magnetic free energy difference ΔG m between different crystallographic axes of the material is eater than a thermal energy kT;

while applying the magnetic field, cooling the melt at a rate of about 30° C./min or higher; and

solidifying the melt to form a single crystal of the material, wherein the material comprises:

25-30 wt. % Ni,

14-20 wt. % Co,

9-13 wt. % Al,

up to about 3 wt. % Ta,

up to about 0.07 wt. % B; and

the balance Fe.

15. A magnetocaloric device comprising:

an iron-based composition comprising:

25-30 wt. % Ni,

14-20 wt. % Co,

9-13 wt. % Al,

up to about 3 wt. % Ta,

up to about 0.07 wt. % B; and

the balance Fe,

wherein the iron-based composition comprises a crystallite density of no more than about 1 grain/mm 2 .

16. The magnetocaloric device of claim 15 , wherein the iron-based composition comprises:

28 wt. % Ni,

17 wt. % Co,

11.5 wt. % Al,

2.5 wt. % Ta, and

0.05 wt. % B.

17. The magonetocaloric device of claim 15 comprising a single crystal comprising the iron-based composition and having a size of at least about 15 cm 3 .

18. The magnetocaloric device of claim 15 , wherein the iron-based composition comprises a single crystalline structure.