title: Spontaneous demagnetization of a dipolar spinor Bose gas in an ultralow magnetic field.
abstract: We study the spinor properties of S = 3 (52)Cr condensates, in which dipole-dipole interactions allow changes in magnetization. We observe a demagnetization of the Bose-Einstein condensate (BEC) when the magnetic field is quenched below a critical value corresponding to a phase transition between a ferromagnetic and a nonpolarized ground state, which occurs when spin-dependent contact interactions overwhelm the linear Zeeman effect. The critical field is increased when the density is raised by loading the BEC in a deep 2D optical lattice. The magnetization dynamics is set by dipole-dipole interactions.
authors.affiliation: Laboratoire de Physique des Lasers, CNRS UMR 7538, Université Paris 13, 99 Avenue J-B Clément, 93430 Villetaneuse, France.
authors.forename: B
authors.initials: B
authors.lastname: Pasquiou
authors.forename: E
authors.initials: E
authors.lastname: Maréchal
authors.forename: G
authors.initials: G
authors.lastname: Bismut
authors.forename: P
authors.initials: P
authors.lastname: Pedri
authors.forename: L
authors.initials: L
authors.lastname: Vernac
authors.forename: O
authors.initials: O
authors.lastname: Gorceix
authors.forename: B
authors.initials: B
authors.lastname: Laburthe-Tolra