  In this paper we present the microscopic origin of the ferromagnetism of
Fe0.25TaS2 and its finite-temperature magnetic properties. We first obtain the
band structures of Fe0.25TaS2 by the first-principles calculations and find
that both conventional and Dirac carriers coexist in metallic Fe0.25TaS2.
Accordingly, considering the spin-orbit coupling of Fe 3d ion, we derive an
effective RKKY-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 Tc 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
FexTaS2.
