Large negative thermal expansion in high-strength MnNiFeSi/Cu composites with continuous Cu networks

MM'X intermetallics with magneto-structural transformations related to phase transformation have potential in refrigeration and negative thermal expansion applications. However, the application of these intermetallics is severely limited by poor mechanical properties. In this study, we designed and prepared a magnetocaloric composite material composed of Mn0.41Ni0.79Fe0.8Si particles embedded in a continuous Cu network. The intermetallic powder is chemically plated with copper and subsequently subjected to spark plasma sintering to achieve a dense microstructure. The prepared composite materials not only reach a compressive strength of 646 MPa and a negative thermal expansion coefficient of −103 ppm K−1 but also retain their inherent magnetocaloric effect. This study shows that the construction of a continuous copper network is a feasible microstructural method that can enhance mechanical integrity, thus improving its prospects in magnetic multifunctional applications.