Phase transitions and critical properties in systems of interacting multicomponent magnetic bosons

A d-dimensional model of multicomponent interacting bosons with spin S and a magnetic moment in the presence of a magnetic field H is studied by means of a large-n limit treatment and a renormalization group approach, in the spirit of critical phenomena theory. Magnetic phase transitions and a ferromagnetic state with a zero-field divergent susceptibility and an exotic criticality are shown to occur, as in the noninteracting model, strictly related to the onset of the Bose-Einstein condensation. The bosonic and magnetic properties of the system are explored by approaching a critical line which marks, for H ≠ 0, the occurrence of Bose-Einstein transitions together with magnetic ones whose order, greater than two, depends on the ratio d/θ, where 0 < θ ≤ 2 is connected to the range of interactions (in the n-vector classical counterpart).