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 ErCrO3were 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 ErCrO3was 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.