Magnetic heat pumping near room temperature

Magnetic heat pumping can be made practical at room temperature by using a ferromagnetic material with a Curie point in or near the operating temperature range and an appropriate regenerative thermodynamic cycle. Rare earths are found to be much more effective in this application than transition elements, and measurements have been made which show that gadolinium (Curie point: 293 °K) is a reasonable working material. The application of a 7-T magnetic field to Gd at the Curie point causes a heat release of 4 kJ/kg under isothermal conditions or a temperature rise of 14 °K under adiabatic conditions. A regeneration technique is proposed which removes the limits usually expected on the temperature span of a magnetic cycle. The cycle efficiency can approach the Carnot-cycle efficiency.