Magnetic Materials and Systems

1 . A material comprising:

a magnetic material exhibiting a metamagnetic transition to a magnetic saturation at an applied magnetic field of strength less than or equal to 1 T, wherein a transition temperature of the magnetic material is within a temperature region from about 160 K to about 350K.

2 . The material of claim 1 , wherein the strength of the applied magnetic field is less than or equal to about 0.75 T.

3 . The material of claim 1 , wherein the temperature region is from about 180K to about 325K.

4 . The material of claim 1 , wherein the magnetic material belongs to cubic D2 3 crystal structure.

5 . The material of claim 1 , wherein the magnetic material comprises a rare earth element, a 3d transition element, a secondary element, and a dopant, wherein the magnetic moment of the dopant is more than the magnetic moment of the rare earth element.

6 . The material of claim 5 , wherein the magnetic material comprises lanthanum, iron, silicon, and the dopant.

7 . The material of claim 6 , wherein the dopant comprises a rare earth element, a 3d transition element, or a combination thereof.

8 . The material of claim 7 , wherein the rare earth element dopant comprises gadolinium, terbium, dysprosium, praseodymium, holmium, erbium, or a combination thereof.

9 . The material of claim 7 , wherein the 3d transition element dopant comprises vanadium, chromium, manganese, iron, cobalt, nickel, copper, zinc, or combinations thereof.

10 . The material of claim 5 , wherein the magnetic material further comprises an interstitial element.

11 . The material of claim 10 , wherein the interstitial element comprises hydrogen, carbon, boron, nitrogen, or combinations thereof.

12 . The material of claim 5 , wherein the dopant is present in an amount in the range from about 1 atomic percent to about 15 atomic percent.

13 . The material of claim 12 , wherein the dopant is present in an amount in the range from about 3 atomic percent to about 12 atomic percent.

14 . A thermal transfer device comprising the material of claim 1 .

15 . The thermal transfer device of claim 14 , comprising a refrigerator, an air conditioner, a thermal management device, a heat sink, or a combinations thereof.

16 . A material comprising:

a magnetic material comprising gadolinium, terbium, dysprosium, praseodymium, holmium, erbium, or a combination thereof in a range from about 3 atomic percent to about 12 atomic percent, and exhibiting a metamagnetic transition to a magnetic

saturation at an applied magnetic field of strength less than or equal to 1 T, wherein the transition temperature of the magnetic material is within a temperature region from about 160 K to about 350K.

17 . The material of claim 1 , wherein the magnetic material belongs to cubic D2 3 crystal structure and comprises a rare earth element, a 3d transition element, and a metalloid element.

18 . The material of claim 16 , wherein the magnetic material is a doped La( Fe1-y , Si y )13, wherein y≦1.5 and wherein lanthanum is doped with gadolinium, terbium, dysprosium or combinations thereof.

19 . The material of claim 16 , wherein the magnetic material further comprises an interstitial element.

20 . The material of claim 19 , wherein the interstitial element comprises hydrogen, carbon, boron, nitrogen, or combinations thereof.

21 . A thermal transfer device comprising the material of claim 1 .

22 . A magneto-caloric system comprising:

a thermal diffusivity matrix comprising a plurality of miniature structures magnetically coupled to a magnetic field and thermally coupled to a heat transfer fluid, and comprising a material, wherein the material comprises a magnetic material exhibiting a metamagnetic transition to a magnetic saturation at an applied magnetic field of strength less than or equal to 1 T, and wherein a transition temperature of the magnetic material is within a temperature region from about 160 K to about 350K.