Phase separation of ferromagnetic spin-1 Bose gases in non-zero magnetic field

Properties of ferromagnetic spin-1 Bose gases above and at the temperature of Bose-Einstein condensation are studied in the presence of a magnetic field. The equation of state is given in a mean-field approximation. It is found that there exists a critical magnetic field and below that two phases coexist with different particle densities. The stability of the system is also investigated with the help of the susceptibility matrix. The dynamics of the system is worked out in the Random Phase Approximation and the soft mode corresponding to the critical point is given.