Anisotropic magnetoelastic coupling and magnetocaloric effect in the Fe$_{5}$Si$_{3}$-type hexagonal single crystal

The structural, magnetic properties, and the magnetocaloric effect (MCE) of Fe$_{5}$Si$_{3}$ single crystal with trace of Mn and P doping (Fe$_{4.83}$Mn$_{0.16}$Si$_{2.91}$P$_{0.09})$ are investigated. A first-order magneto-elastic transition was found at the magnetic transition temperature $T_{C}$, with the magnetic easy axis lying in the ab plane. While the trace of Mn and P doping in the Fe$_{5}$Si$_{3}$ single crystal was found to increase both the maximum magnetic entropy change and relative cooling power from those in polycrystalline Fe$_{5}$Si$_{3}$ compound, indicating the intrinsic broaden entropy change in larger temperature span. The anisotropy in the MCE between H//ab and H//c is observed, which originates from the anisotropic spin-lattice coupling between the ab plane and the c axis. The density functional theory calculations were performed to gain microscopic insights into the experimental findings. Our results suggest hexagonal Fe$_{5}$Si$_{3}$ system may become a new candidate of giant MCE as La-Fe-Si and Fe-Mn-P-Si systems.