  Quantum degenerate Bose gases with an internal degree of freedom, known as
spinor condensates, are natural candidates to study the interplay between
magnetism and superfluidity. In the spinor condensates made of alkali atoms
studied so far, the spinor properties are set by contact interactions, while
magnetization is dynamically frozen, due to small magnetic dipole-dipole
interactions. Here, we study the spinor properties of S=3 $^{52}$Cr atoms, in
which relatively strong dipole-dipole interactions allow changes in
magnetization. We observe a phase transition between a ferromagnetic phase and
an unpolarized phase when the magnetic field is quenched to an extremely low
value, below which interactions overwhelm the linear Zeeman effect. The BEC
magnetization changes due to magnetic dipole-dipole interactions that set the
dynamics. Our work opens up the experimental study of quantum magnetism with
free magnetization using ultra-cold atoms.
