Rational design of MnCoGe alloys for enhanced magnetocaloric performance and reduced thermal hysteresis

MnCoGe alloys are widely recognized as an important family of rare-earth-free magnetocaloric materials by engineering its magnetostructural coupling for giant entropy changes. However, its practicability for magnetic refrigeration is largely hindered by the large thermal hysteresis. In this work, we show that the co-doped MnCoGe compound, namely Mn_0.95Cu_0.03CoGe with 2 both mol% Mn vacancies and 3 mol% Cu-doping for Mn, displays a maximum entropy change of 29.0 J kg⁻¹K⁻¹ at 295 K under a magnetic field of 5 T, together with a relative cooling power as high as 314.5 J kg⁻¹ and a record low thermal hysteresis of 16 K. The co-doping strategy in MnCoGe finely tunes the structural transition temperature within the range of Curie temperature window, leading to a strong magnetostructural coupling and giant magnetocaloric effect. Meanwhile, Mn-deficiency and Cu-doping considerably reduce the energy difference between martensitic and austenitic MnCoGe, rendering a minimal thermal hysteresis. Our co-doped MnCoGe alloys are robust candidates for near-room-temperature magnetic refrigeration.