Emergent evolution of first-order phase transitions from magneto-structural to magneto-elastic in MnCo_1−y Fe _y Ge_1−x Si _x alloys

Abstract The emergent evolution of first-order phase transitions from magneto-structural to magneto-elastic and magnetocaloric effect (MCE) have been investigated by X-ray diffraction, differential scanning calorimetry and magnetization measurements. Applying the isostructural alloying principle, the martensitic transition temperature ( T M ) increases effectively and the Curie temperatures of the two phases increase slightly by substituting the Si content ( x ). With an appropriate amount of Fe and Si content, an emergent first-order antiferromagnetic–ferromagnetic magnetoelastic transition with thermal hysteresis in the martensitic state occurs for MnCo 0.7 Fe 0.3 Ge 1– x Si x ( x = 0.15–0.40) alloys, which results from the decrease in the nearest-neighbor Mn–Mn distance. Moreover, the values of magnetic entropy change (Δ S M ), refrigeration capacity (RC) and temperature-averaged entropy change (TEC, 10 K) with Δ H = 50 kOe reach −12.2 J kg −1 K −1 , 112.8 J kg −1 and 11.4 J kg −1 K −1 for MnCo 0.7 Fe 0.3 Ge 0.8 Si 0.2 undergoing the ferromagnetic magneto-structural transition in the Curie temperature window. The results facilitate the magnetocaloric/magnetoelastic performance and tunability of multiple phase states in a wider temperature range.