Magnetic topological Weyl fermions in half-metallic In$_2$CoSe$_4$

Magnetic Weyl semimetals (WSM) have recently attracted much attention due to their potential in realizing strong anomalous Hall effects. Yet, how to design such systems remains unclear. Based on first-principles calculations, we show here that the ferromagnetic half-metallic compound In$_2$CoSe$_4$ has several pairs of Weyl points and is hence a good candidate for magnetic WSM. These Weyl points would approach the Fermi level gradually as the Hubbard $U$ increases, and finally disappear after a critical value $U_c$. The range of the Hubbard $U$ that can realize the magnetic WSM state can be expanded by pressure, manifesting the practical utility of the present prediction. Moreover, by generating two surface terminations at Co or In atom after cleaving the compound at the Co-Se bonds, the nontrivial Fermi arcs connecting one pair of Weyl points with opposite chirality are discovered in surface states. Furthermore, it is possible to observe the nontrivial surface state experimentally, e.g., angle-resolved photoemission spectroscopy (ARPES) measurements. As such, the present findings imply strongly a new magnetic WSM which may host a large anomalous Hall conductivity.