Effect of co-doping on martensite transformation hysteresis of Ni-Mn-Sn ferromagnetic shape memory alloys

Ni-Mn-Sn ferromagnetic shape memory alloys, which exhibit a large magnetic entropy change ( ΔS ), are highly promising for solid-state magnetic refrigeration. However, their large thermal hysteresis ( ΔT _hys ) severely reduces the effective refrigeration capacity and thus hinders their solid-state refrigeration applications. Here, the effect of Co-doping on the reduced ΔT _hys is demonstrated in a Ni_41.0Mn_43.5Sn_10.5Co_5.0 (Co5.0) alloy. The significantly reduced ΔT _hys of 5.2 K can be attributed to the ideal geometrical compatibility between the martensite and austenite phases (| λ ₂–1| = 0.0008 ± 0.0002). In addition, the Co5.0 alloy exhibits a martensite transformation (MT) equivalent temperature ( T ₀ = ( M _s + A _f)/2 = 284.5 K) near room temperature. Under a magnetic field change of 5 T, the Δ S of 28.7 J kg⁻¹ K⁻¹, refrigeration capacity ( RC) of 325.9 J kg⁻¹ and relative cooling power ( RCP ) of 364.5 J kg⁻¹ are obtained in Co5.0 alloy. This work provides experimental guidance for developing low-hysteresis, near-room temperature high-performance magnetocaloric materials.