Challenges to magnetic doping of thin films of the Dirac semimetal Cd3As2

Magnetic doping of topological quantum materials provides an attractive route for studying the effects of time-reversal symmetry breaking. Thus motivated, we explore the introduction of the transition metal Mn into thin films of the Dirac semimetal ${\mathrm{Cd}}₃{\mathrm{As}}₂$ during growth by molecular beam epitaxy. Scanning transmission electron microscopy measurements show the formation of a Mn-rich phase at the top surface of Mn-doped ${\mathrm{Cd}}₃{\mathrm{As}}₂$ thin films grown using both uniform doping and delta doping. This suggests that Mn acts as a surfactant during epitaxial growth of ${\mathrm{Cd}}₃{\mathrm{As}}₂$, resulting in phase separation. Magnetometry measurements of such samples indicate a ferromagnetic phase with out-of-plane magnetic anisotropy. Electrical magneto-transport measurements of these films as a function of temperature, magnetic field, and chemical potential reveal a lower carrier density and higher electron mobility compared with pristine ${\mathrm{Cd}}₃{\mathrm{As}}₂$ films grown under similar conditions. This suggests that the surfactant effect might also serve to remove impurities from the bulk of the film. We observe robust quantum transport (Shubnikov-de Haas oscillations and an incipient integer quantum Hall effect) in very thin (7 nm) ${\mathrm{Cd}}₃{\mathrm{As}}₂$ films despite being in direct contact with a structurally disordered surface ferromagnetic overlayer.