Kinetic origin of hysteresis and the strongly enhanced reversible barocaloric effect by regulating the atomic coordination environment

Abstract

Hysteresis is an inherent property of first-order transition materials that poses challenges for solid-state refrigeration applications. Extensive research has been conducted, but the intrinsic origins of hysteresis remain poorly understood. Here, we report a study of the kinetic origin of hysteresis and the enhanced barocaloric effect (BCE) in MnCoGe-based alloys with ~2% nonmagnetic In atoms. First-principles calculations demonstrate that substituting In atoms at Ge sites rather than Co sites results in a lower energy barrier, indicating a narrower hysteresis for the former. Combining neutron powder diffraction (NPD) with magnetic and calorimetric measurements completely verified the theoretical prediction. Electron local function (ELF) calculations further reveal the atomic coordination origin of regulated hysteresis due to weaker Co–Ge bonds when In atoms replace Ge, which is opposite to Co sites. Moreover, we experimentally investigate the BCE and find that although MnCo(Ge0.98In0.02) has a lower barocaloric entropy change ΔSP than does Mn(Co0.98In0.02)Ge, the reversible ΔSrev of the former is advantageous owing to a smaller hysteresis. The maximum ΔSrev of MnCo(Ge0.98In0.02) is 1.7 times greater than that of Mn(Co0.98In0.02)Ge. These results reveal the atomic-scale mechanism regulating hysteresis and provide insights into tailoring the functional properties of novel caloric refrigeration materials. First-principles calculations demonstrated that the substitution of In for Ge has a lower energy barrier for phase transition than the substitution of In for Co in MnCoGe alloys. ELF calculations further reveal the regulated hysteresis’s atomic coordination origin. This theoretical prediction is completely verified by combining neutron, magnetic and calorimetric measurements; consequently, a largely enhanced barocaloric effect has been achieved. Hysteresis is an inherent property of first-order transition materials that poses challenges for solid-state refrigeration applications. Here we report a study of the kinetic origin of hysteresis and enhanced barocaloric effect (BCE) in MnCoGe-based alloys with about 2% non-magnetic In atoms. First-principles calculations demonstrated that the substitution of In for Ge has a lower energy barrier of phase transition than the substitution of In for Co in MnCoGe alloys, indicating a narrower hysteresis for the former. Electron local function (ELF) calculations further reveal the atomic coordination origin of regulated hysteresis due to weaker Co-Ge bonds when In atoms replaced Ge, opposite to Co sites. Such theoretical prediction is completely verified by combining neutron with magnetic and calorimetric measurements, consequently strongly enhanced reversible BCE has been achieved. These results uncover the atomic-scale mechanism regulating hysteresis and provide insights for tailoring functional properties of novel caloric refrigeration materials.