  The pyrite compound CoS2 has been intensively studied in the past due to its
itinerant ferromagnetism and potential for half-metallicity, which make it a
promising material for spintronic applications. However, its electronic
structure remains only poorly understood. Here we use complementary bulk- and
surface-sensitive angle-resolved photoelectron spectroscopy and ab-initio
calculations to provide a complete picture of its band structure. We discover
Weyl-cones at the Fermi-level, which presents CoS2 in a new light as a rare
member of the recently discovered class of magnetic topological metals. We
directly observe the topological Fermi-arc surface states that link the
Weyl-nodes, which will influence the performance of CoS2 as a spin-injector by
modifying its spin-polarization at interfaces. Additionally, we are for the
first time able to directly observe a minority-spin bulk electron pocket in the
corner of the Brillouin zone, which proves that CoS2 cannot be a true
half-metal. Beyond settling the longstanding debate about half-metallicity in
CoS2, our results provide a prime example of how the topology of magnetic
materials can affect their use in spintronic applications.
