  We investigate an ultra-cold mixture of Bose gases interacting via
spin-changing collisions by studying the dynamics of spin fluctuations. The
experimental implementation employs $^{23}$Na and $^{7}$Li atoms, which are
prepared out of equilibrium across a wide range of initial conditions. We
identify three regimes in the dynamics of the system for different initial
states: a long-lived metastable regime, an instability range with strong growth
of fluctuations, and a fast relaxing regime approaching thermal equilibrium.
Theoretical modelling of the data allows us to reconstruct effective potentials
which characterize the different dynamical regimes of the system.
