  We study the emergence of itinerant ferromagnetism in an ultra-cold atomic
gas with a variable mass ratio between the up and down spin species. Mass
imbalance breaks the SU(2) spin symmetry leading to a modified Stoner
criterion. We first elucidate the phase behavior in both the grand canonical
and canonical ensembles. Secondly, we apply the formalism to a harmonic trap to
demonstrate how a mass imbalance delivers unique experimental signatures of
ferromagnetism. These could help future experiments to better identify the
putative ferromagnetic state. Furthermore, we highlight how a mass imbalance
suppresses the three-body loss processes that handicap the formation of a
ferromagnetic state. Finally, we study the time dependent formation of the
ferromagnetic phase following a quench in the interaction strength.
