Microstructure, magnetism and critical behavior of hot pressed Ni-Mn-Ga/Al magnetocaloric composites with enhanced thermal conductivity and mechanical properties

Abstract

In the application of magnetic refrigeration technology, magnetocaloric materials are required to possess large magnetocaloric effect and broad working temperature range with good thermal conductivity and mechanical properties. To address this elusive combination of properties, we prepared Ni-Mn-Ga/Al magnetocaloric composites via hot pressing method. Phase composition and element distribution revealed the influence of sintering temperature on composites' microstructure. The magnetic properties and magnetocaloric effect of hot pressed Ni-Mn-Ga alloy and Ni-Mn-Ga/Al composites were studied, indicating their largely broadened working temperature range of 71 K and maximum magnetic entropy change of 2.2–3.0 J/(kg K). Based on thermomagnetic measurements, critical behavior was investigated via modified Arrott plots and Kouvel-Fisher method, and mean-field theory model could best explain the samples' critical behavior. The Ni-Mn-Ga/Al composite also possessed enhanced fracture stress of 306 MPa, much higher than that of bulk Ni-Mn-Ga alloy by arc melting. The good magnetocaloric response of the composites, which is comparable or even better than that of many other Ni-Mn-Ga particle and microwire counterparts, is accompanied by improved thermal conductivity and mechanical properties, extending the applicability of magnetocaloric materials with large specific surface area. The novel findings of this systematic study offer new insights into magnetocaloric composites and provide an approach to reach a significant balance when fulfilling multiple requirements of magnetic refrigeration technology. • Hot pressed Ni-Mn-Ga/Al was thoroughly studied in view of refrigeration application. • HP samples had good MCE comparable to their counterparts with reduced length scale. • MAP and KF method were used to compute critical exponents and study critical behavior. • Order of phase transition was ascertained by both Banerjee criterion and exponent n. • Thermal conductivity and mechanical properties were improved after making composites.