  Based on classical density functional theory (DFT), we investigate the
demixing phase transition of a two-dimensional, binary Heisenberg fluid
mixture. The particles in the mixture are modeled as Gaussian soft spheres,
where one component is characterized by an additional classical spin-spin
interaction of Heisenberg type. Within the DFT we treat the particle
interactions using a mean-field approximation. For certain magnetic coupling
strengths we calculate phase diagrams in the density-concentration plane. For
sufficiently large coupling strengths and densities, we find a demixing phase
transition driven by the ferromagnetic interactions of the magnetic species. We
also provide a microscopic description (i.e., density profiles) of the
resulting non-magnetic/magnetic fluid-fluid interface. Finally, we investigate
the phase separation using dynamical density functional theory (DDFT),
considering both nucleation processes and spinodal demixing.
