After the discovery of 2D Dirac semimetals, the search for the 3D Dirac semimetal with a simple electronic structure continues. In topological Dirac semimetals, the bulk conduction and valence bands touch only at discrete (Dirac) points and disperse linearly along all three momentum directions, forming bulk (3D) Dirac fermions—a natural 3D counterpart of graphene. In addition to these bulk Dirac cones, some Dirac semimetals also possess topological non-trivial surface states, similar to those found in topological insulators. This unique electronic structure of topological Dirac semimetals gives rise to many unusual properties, such as the giant diamagnetism, giant linear magnetoresistance, oscillating quantum spin Hall effect and ultrahigh carrier mobility. In addition, an external magnetic field or magnetic doping in these materials can implement the breaking of the time-reversal symmetry, resulting Weyl semimetal phase. Therefore, here we proposed to investigate how the topological state (Dirac or Weyl) of semimetals can be tuned via its magnetic state. The overall objective of the project is to understand the interplay between magnetism and topological state of Dirac semimetals. This involves the growth of high quality single-crystalline thin films of 3D Dirac semimetals and controlling their magnetic state via magnetic doping.