Direct measurement of the magnetocaloric effect (Delta T-ad) of Mn5-x (Fe, Co)(x)Ge-3

Abstract

Magnetic field-induced adiabatic temperature change, Delta T-ad, measures the temperature gradient that enables a magnetic refrigerant to transfer heat from reservoirs. The Delta T-ad of Mn5Ge3 was evaluated by directly recording the temperature of a Mn5Ge3 sample while subjecting it to an external field. The peak Delta T-ad of 0.89 +/- 0.006 at 0.8 T for Mn5Ge3 at its Curie temperature was consistent with the value previously obtained from specific heat capacity measurements. In addition, the peak values of Delta T-ad for Mn4.75Co0.25Ge3 and Mn4.75Fe0.25Ge3 were measured to be 0.77 +/- 0.009 and 0.93 +/- 0.011, respectively, at 0.8 T near their respective Curie temperatures. Delta T-ad measurements under cyclic application of a 0.8 T field showed that the alloys, whose magnetocaloric effect stems from the second-order magnetic phase transition, exhibited no hysteresis in Delta T-ad and maintained their peak Delta T-ad within 1.3% under cyclic field. The Delta T-ad of sandwiched Mn4.75Co0.25Ge3 and Mn4.75Fe0.25Ge3 plates was also measured to demonstrate that a combination of the alloys can be used to form a graded regenerator for the active magnetic regenerator cycle.