Magnetocaloric refrigerant with wide operating temperature range based on Mn5−xGe3(Co,Fe)x composite

The Curie temperature of Mn5Ge3 was raised or lowered by alloying the compound with Fe or Co; hence, the temperature at which maximum magnetocaloric effect manifested was easily manipulated by forming Mn5−xGe3(Co,Fe)x alloys to ultimately develop a composite magnetic refrigerant consisting of multiple Mn5Ge3 - based alloys. The composite refrigerant was designed to produce a table-like ΔSM-T curve and to maximize the RC value near room temperature. Linear combination of the ΔSM-T curves for the constituent materials showed that a composite composed of physical mixture of four different Mn5Ge3-based compounds: Mn5Ge3, Mn5.1Ge2.9, Mn4.75Co0.25Ge3 and Mn4.75Fe0.25Ge3, generated an optimal ΔSM-T curve with a table-like shape. The composite refrigerant with refrigeration capacity of 52 J kg−1, peak entropy change at 300 K, and operating temperature range of 45 K under ΔH = 10 kOe was suitable for room-temperature magnetic refrigeration. Moreover, by changing the relative fraction of each constituent material in the composite, it was shown that the operating temperature range could be fine-tuned as needed. The calculated ΔSM-T curve for the composite refrigerant by linear combination reasonably well matched the experimental ΔSM-T curve estimated from the M-H curves of the composite refrigerant, suggesting that the simple linear combination of the experimental ΔSM-T curves can be used to predict the performance of the composite magnetic refrigerants whose MCE was originated from the second order magnetic transition. In conclusion, being rare-earth free and lacking thermal or magnetic hysteresis, the Mn5Ge3 - based composite can be a competitive candidate magnetic refrigerant material operating at room temperature in terms of both economy and reliability compared to the giant MCE materials such as Gd - based intermetallic compounds or Heusler alloys.