  We experimentally investigate the dynamics of spin solitary waves (magnetic
solitons) in a harmonically trapped, binary superfluid mixture. We measure the
in-situ density of each pseudospin component and their relative local phase via
an interferometric technique we developed, and as such, fully characterise the
magnetic solitons while they undergo oscillatory motion in the trap. Magnetic
solitons exhibit non-dispersive, dissipationless long-time dynamics. By
imprinting multiple magnetic solitons in our ultracold gas sample, we engineer
binary collisions between solitons of either same or opposite magnetisation and
map out their trajectories.
