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

Abstract

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 52Jkg−1, peak entropy change at 300K, and operating temperature range of 45K under ΔH=10kOe 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.