Grain-orientation engineering enables dual-functionality in (Mn,Fe)2(P,Si)/epoxy composites: Colossal negative thermal expansion and anisotropic magnetocaloric effect

The (001)-oriented (Mn,Fe)2(P,Si)/epoxy composites were fabricated via magnetic field-assisted dynamic self-assembly. These textured composites demonstrate remarkable adaptability for diverse applications that require either substantial coefficients (alpha l) of negative thermal expansion (NTE) or broad NTE temperature windows (Delta TNTE). A two-dimensional NTE with a colossal alpha l of-144.37 x 10-6 K-1 is realized between 280 and 360 K in the composite displaying a first-order phase transition (FOPT). The Delta TNTE can be significantly extended to 190 K (120-310K) in the composite exhibiting a second-order phase transition (SOPT), while preserving a large alpha l of-23.89 x 10-6 K-1. Besides that, anisotropic MCE is observed in the textured composites. The FOPT composite exhibits a maximum entropy change of 7.18 Jkg-1 K-1 under a magnetic field of 1 T applied perpendicular to the texture direction, which is 34 % higher than the parallel field configuration. Consequently, our study demonstrates that grain-orientation engineering can be effectively employed to explore NTE and achieve anisotropic magnetocaloric properties.