Magnetic cooling by an adiabatic spin reorientation

A new method of magnetic cooling is proposed by using an adiabatic entropy change associated with a spin reorientation transition. This is available for a magnetic refrigerator operating under a weaker magnetic field than an ordinary method using a superconducting magnet to cool a paramagnetic crystal. The single crystal and sintered samples of ErCrO
3
were adopted as a prototype material. The sample was set in the adiabatic cell and put in a sweeping magnetic field. The cooling was observed in the range from 2 to 11 K. A maximum cooling of 0.4 degrees was obtained for the single crystal just below the transition temperature TSR (= 9.8 K) in a magnetic field of 200 Oe after applying the correction of the demagnetizing effect. The entropy vs temperature diagram of ErCrO
3
was determined from measurements of the specific heat. The complete analogy between thermodynamic properties of the spin reorientation transition with those of a liquid-gas system suggests a possibility of an application to a heat engine. Such a device might be useful for maintaining a temperature lower than the transition temperature by a permanent magnet.