Magnetocaloric cascade and method for fabricating a magnetocaloric cascade

1. A magnetocaloric cascade, comprising:

a sequence of magnetocaloric material layers having different Curie temperatures T C ,

wherein the magnetocaloric material layers include a cold-side outer layer, a hot-side outer layer and at least three inner layers between the cold-side outer layer and the hot-side outer layer, and each pair of next neighboring magnetocaloric layers of the magnetocaloric cascade has a respective Curie-temperature difference amount ΔT C between their respective Curie temperatures, and

wherein the hot-side outer layer or the cold-side outer layer or both the hot-side and cold-side outer layer exhibits a larger ratio mΔS max /ΔT C in comparison with any of the inner layers, m denoting the mass of the respective magnetocaloric material layer and ΔS max denoting a maximum amount of isothermal magnetic entropy change achievable in a magnetic phase transition of the respective magnetocaloric material layer.

2. The magnetocaloric cascade of claim 1 , wherein the hot-side outer layer or the cold-side outer layer exhibits an amount of the ratio mΔS max /ΔT C that is at least 1% larger in comparison with any of the inner layers.

3. The magnetocaloric cascade of claim 1 , wherein one of the hot-side and cold-side outer layers has a higher amount of the ratio mΔS max /ΔT C than the other, and wherein the other of the hot-side and cold-side outer layers has a higher amount of the ratio mΔS max /ΔT C than any of inner layers.

4. The magnetocaloric cascade of claim 1 , wherein the hot-side outer layer or the cold-side outer layer exhibits an amount of a product mΔS max of its mass and ΔS max , the amount of mΔS max being larger by at least 10% in comparison with any of the inner layers.

5. The magnetocaloric cascade of claim 1 , wherein the hot-side layer or the cold-side layer exhibits a smaller amount of ΔT C in comparison with any of the inner layers.

6. The magnetocaloric cascade of claim 5 , wherein the hot-side layer or the cold-side layer exhibits an amount of ΔT C that is no less than 0.5 K.

7. The magnetocaloric cascade of claim claim 1 , wherein the hot-side outer layer or the cold-side outer layer or both the hot-side and cold-side outer layer comprises a sublayer sequence of at least two hot-side sublayers or cold-side sublayers, respectively.

8. The magnetocaloric cascade of claim 1 , wherein for each pair of next neighboring magnetocaloric material layers of the magnetocaloric cascade there exists a respective crossing temperature, at which an entropy parameter mΔS of both respective neighboring magnetocaloric material layers assumes the same crossing-point value, the entropy parameter mΔS being defined as a product of the mass m of the respective magnetocaloric material layer and an amount of its isothermal magnetic entropy change ΔS in a magnetic phase transition of the respective magnetocaloric material layer; and wherein

all crossing-point values of an entropy parameter mΔS of all pairs of next neighboring inner layers are equal, either exactly or within a margin of ±15%, to a mean value of all crossing-point values of all pairs of next neighboring inner layers of the magnetocaloric cascade.

9. The magnetocaloric cascade of claim 8 , wherein different inner layers exhibit respective materials and respective masses which in combination provide the respective crossing-point values of the entropy parameter mΔS at no less than 70% of a global maximum of the entropy parameter mΔS assumed in any of the inner layers across the magnetocaloric cascade.

10. A magnetocaloric regenerator, comprising:

the magnetocaloric cascade according to claims 1 .

11. A heat pump, comprising: a magnetocaloric regenerator according to claim 10 .

12. The heat pump of claim 11 , further comprising:

a hot-side interface in thermal communication with the hot-side outer layer,

a cold-side interface in thermal communication with the cold-side outer layer, and

a heat transfer system, which is configured to provide a flow of a heat-transfer fluid between the hot-side interface and the cold side interface through the magnetocaloric cascade,

wherein the Curie temperature of the hot-side outer layer is selected to be higher than a temperature of the hot-side interface in operation of the heat pump, or the Curie temperature of the cold-side outer layer is selected to be lower than a temperature of the cold-side interface in operation of the heat pump.

13. A method for fabricating a magnetocaloric cascade, comprising:

fabricating a sequence of different magnetocaloric material layers having different Curie temperatures T C , wherein the magnetocaloric material layers include a cold-side outer layer, a hot-side outer layer and at least three inner layers between the cold-side outer layer and the hot-side outer layer and each pair of next neighboring magnetocaloric layers of the magnetocaloric cascade has a respective Curie-temperature difference amount ΔT C between their respective Curie temperatures, wherein

the hot-side outer layer or the cold-side outer layer or both the hot-side and cold-side outer layer are fabricated so as to exhibit a larger ratio mΔS max /ΔT C in comparison with any of the inner layers, m denoting the mass of the respective magnetocaloric material layer and ΔS max denoting a maximum amount of isothermal magnetic entropy change achievable in a magnetic phase transition of the respective magnetocaloric material layer.

14. A heat-pumping method, comprising:

performing a heat-pumping sequence using a magnetocaloric regenerator comprising a magnetocaloric cascade according to claim 1 .

15. The heat-pumping method of claim 14 , wherein the heat-pumping sequence includes a temperature increase of the magnetocaloric regenerator and—the heat-pumping sequence is performed in thermal communication with a heat sink, which is operated at a temperature that is between 0.5 K and 5 K higher than a Curie temperature of the hot-side outer layer.