Manipulation of thermal hysteresis and magnetocaloric effect in the Ni-Co-Mn-In alloys through lattice contraction: Effect of Ge substitution for In

First-order magnetostructural transformation can be utilized to generate giant magnetocaloric effect for the magnetic refrigeration applications, but the intrinsic hysteresis always cripples the refrigeration efficiency. In this work, the strategy of lattice contraction was exploited to manipulate the thermal hysteresis and magnetocaloric response in the Ni-Co-Mn-In magnetocaloric alloys. Such strategy was effectuated by using Ge to replace In on account of the relatively smaller atomic radius of Ge, yielding a significant reduction in the thermal hysteresis. In a Ni ₄₆Co ₃Mn ₃₇In ₁₀Ge ₄ alloy with the combination of low thermal hysteresis of ∼4 K and large magnetization difference of 83.1 Am ²kg ⁻¹ associated with the magnetostructural transformation, giant effective refrigeration capacity RC_eff of 311 Jkg ⁻¹ and reversible entropy change Δ S_M up to 22.8 Jkg ⁻¹K ⁻¹ were demonstrated by varying the field of 5 T. Besides, a large reversible adiabatic temperature change Δ T_ad of –3.0 K was also obtained by using a low field change of 1.5 T. Based on the displacement gradient tensor determined by the orientation relationship governing the martensitic transformation, it was presented that Ge substation for In effectively decreased the lattice misfit, thus lowering the elastic energy accompanying the structural transformation and the related transformation hysteresis.