Double perovskite Ba$_2$CdReO$_6$: a ferromagnetic topological semi-half-metal with coexistence of Weyl and nodal-ring states

Magnetic topological quantum materials have attracted great attention due to their exotic topological quantum physics induced by the interplay among crystalology, magnetism, and topology, which are of profound importance to fundamental research and technology applications. However, limited materials are experimentally available, most of whom are realized by magnetic impurity doping or heterostructural constructions. In this work, based on the first-principles calculations, we predict that double perovskite Ba$_2$CdReO$_6$ is an intrinsic ferromagnetic topological semi-half-metal with a pair of Weyl points and fully spin-polarized nodal-ring states in the vicinity of the Fermi level. Its two-dimensional nearly flat drumhead surface states are completely spin-polarized, which would provide a wonderful platform to study the emerging intriguing properties, especially for the applications in spintronics, information technology, and topological superconductivity.