A phenomenological model is proposed to describe the behavior of spinor
Bose-Einstein condensates. In the absence of hyperfine spin-spin interactions,
Bose-Einstein condensation leads to a spontaneous magnetization at the same
transition temperature. This is the so-called Bose-Einstein ferromagnetism.
Including the hyperfine spin interactions, the phase diagram of the spinor
condensate in an optical trap is studied and the Gross-Pitaevskii equation is
extended. The possibility of checking for the existence of the Bose-Einstein
ferromagnetism experimentally is also discussed.Comment: 4 pages, 1 figure, extended discussions, added reference
