Achieving Tunable High‐Performance Giant Magnetocaloric Effect in Hexagonal Mn‐Fe‐P‐Si Materials through Different <i>D</i>‐Block Doping

Abstract Compared with traditional techniques, solid‐state magnetocaloric phase transition materials (MPTMs), based on the giant magnetocaloric effect (GMCE), can achieve a higher energy conversion efficiency for caloric applications. As one of the most promising MPTMs, the hexagonal (Mn,Fe) 2 (P,Si)‐based compounds host some advantages, but the existing hysteresis and relatively unstable GMCE properties need to be properly tackled. In this study, it is found that substitutions with Ni, Pd, and Pt can maintain and even enhance the GMCE (≈8.7% maximum improvement of |Δ s m |). For a magnetic field change of Δ μ 0 H = 2 T, all samples obtain a |Δ s m | in the range of 20–25 J kg −1 K −1 with a low thermal hysteresis Δ T hys (≤5.6 K). The performance surpasses almost all other (Mn,Fe) 2 (P,Si)‐based materials with Δ T hys (&lt;10 K) reported until now. The occupancy of substitutional Ni/Pd/Pt atoms is determined by X‐ray diffraction, neutron diffraction, and density functional theory calculations. The difference in GMCE properties upon doping is understood from the competition between a weakening of the magnetic exchange interactions and the different degrees of orbital hybridization among 3 d ‐4 d ‐5 d elements. The studies elaborate on the responsible mechanism and provide a general strategy through d ‐block doping to further optimize the GMCE of this materials family.