Tailoring Ni–Co–Mn–Sn Ribbons by Ge Doping for Enhanced Magnetocaloric Effect

Abstract Micro‐grained high surface‐to‐volume ratio thin ribbons of magnetic shape memory Ni 42 Co 8 Mn 39 Sn 11‐ x Ge x ( x = 1, 2, 3) alloys are prepared, and their martensitic transformation (MT) behavior, magnetic and magnetocaloric properties are investigated. X‐ray diffraction reveals that the incorporation of Ge consistently decreases the lattice parameters and the transformation volume change, thereby improving geometric compatibility between martensitic and austenitic crystal lattices. This improvement facilitated a reduction of the thermal hysteresis of MT to a minimum of ≈12.1 K at the Ge concentration of x = 2. Direct measurements of adiabatic temperature changes show that the x = 2 alloy (SnGe2 ribbon) exhibited the highest peak value (≈2 K) at a moderate magnetic field change of 1.96 T. In addition, SnGe2 ribbon demonstrates exceptional isothermal entropy changes of ΔS iso = 35.5 J kg −1 K −1 K at 7 T and 22.8 J kg −1 K −1 K at 2 T, which are competitive with those of bulk alloys and surpassing previously reported melt‐spun ribbons of the Heusler‐type magnetocaloric materials. The significance of intricate microstructure in boosting the magnetocaloric effect is emphasized. These results highlight the substantial potential of Ni–Co–Mn–Sn–Ge thin ribbons as highly effective, micro‐sized magnetocaloric materials for cutting‐edge solid‐state refrigeration systems.