Ferromagnetism in Layered Metallic Fe_1/4TaS_2 in the Presence of Conventional and Dirac Carriers

We present the microscopic origin of the ferromagnetism of Fe_0.25TaS_2 and its finite-temperature magnetic properties. The band structures of Fe_0.25TaS_2 are first obtained by the first-principles calculations and it is found that both conventional and Dirac carriers coexist in metallic Fe_0.25TaS_2. Accordingly, considering the spin-orbit coupling of Fe 3d ion, we derive an effective Ruderman–Kittle–Kasuya–Yosida-type Hamiltonian between Fe spins in the presence of both the conventional parabolic-dispersion and the Dirac linear-dispersion carriers, which contains a Heisenberg-like, an Ising-like and an XY-like term. In addition, we obtain the ferromagnetic Curie temperature T_\rm c by using the cluster self-consistent field method. Our results could address not only the high ferromagnetic Curie temperature but also the large magnetic anisotropy in Fe_xTaS_2.