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

Abstract The Curie temperature of Mn 5 Ge 3 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 Mn 5 − x Ge 3 (Co,Fe) x alloys to ultimately develop a composite magnetic refrigerant consisting of multiple Mn 5 Ge 3 – based alloys. The composite refrigerant was designed to produce a table-like Δ S M – T curve and to maximize the RC value near room temperature. Linear combination of the Δ S M – T curves for the constituent materials showed that a composite composed of physical mixture of four different Mn 5 Ge 3 -based compounds: Mn 5 Ge 3 , Mn 5.1 Ge 2.9 , Mn 4.75 Co 0.25 Ge 3 and Mn 4.75 Fe 0.25 Ge 3 , generated an optimal Δ S M – 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 Δ H  = 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 Δ S M – T curve for the composite refrigerant by linear combination reasonably well matched the experimental Δ S M – T curve estimated from the M–H curves of the composite refrigerant, suggesting that the simple linear combination of the experimental Δ S M – 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 Mn 5 Ge 3 – 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.