It is shown that the ferromagnetic transition takes place always above
Bose-Einstein condensation in ferromagnetically coupled spinor Bose gases. We
describe the Bose ferromagnet within Ginzburg-Landau theory by a "two-fluid"
model below Bose-Einstein condensation. Both the Bose condensate and the normal
phase are spontaneously magnetized. As a main result we show that spin waves in
the two fluids are coupled together so as to produce only one mixed spin-wave
mode in the coexisting state. The long wavelength spectrum is quadratic in the
wave vector k, consistent with usual ferromagnetism theory, and the
spin-wave stiffness coefficient cs​ includes contributions from both the two
phases, implying the "two-fluid" feature of the system. cs​ can show a sharp
bend at the Bose-Einstein condensation temperature.Comment: 4 pages, 1 figur