Mn5−xGe3Nix refrigerant for active magnetic refrigeration

Abstract

Mn5−xNixGe3 (x = 0, 0.025, 0.075, 0.1, 0.15, 0.2, 0.25, and 0.4) alloys were synthesized to demonstrate that the magnetocaloric (MCE) properties [Curie temperature, magnetic entropy change (ΔSM), and adiabatic temperature change (ΔTad)] can be fine-tuned by changing the Ni fraction. An active magnetic regenerative (AMR) cycle testbed was built in-house to investigate the suitability of Mn5−xNixGe3 as a solid magnetic refrigerant operating at room temperature and as a composite refrigerant for an AMR cycle. The maximum temperature difference between the hot and cold ends, ΔTspan, measured from the AMR testbed was 7.5 K and 5.6 K for Gd and Mn5Ge3, respectively. The ΔTspan values were reasonable considering the inferior ΔSM and ΔTad for Mn5Ge3 compared to those of Gd. A two-layer composite refrigerant consisting of Mn5Ge3 and Mn4.975Ni0.025Ge3 produced ΔTspan of 6.3 K, which is 13% higher than that of the single Mn5Ge3 refrigerant, indicating the effectiveness of a multi-layer refrigerant selected to closely match the temperature gradient in an AMR cycle. This work highlights the importance of tailoring the MCE properties as required to build a composite refrigerant.