  We study quantum dynamical properties of a spin-1 atomic Bose-Einstein
condensate in a double-well potential. Adopting a mean field theory and single
spatial mode approximation, we characterize our model system as two coupled
spins. For certain initial states, we find full magnetization oscillations
between wells not accompanied by mass (or atom numbers) exchange. We identify
dynamic regimes of collective spin variables arising from nonlinear
self-interactions that are different from the usual Josephson oscillations. We
also discuss magnetization beats and incomplete oscillations of collective spin
variables other than the magnetization. Our study points to an alternative
approach to observe coherent tunnelling of a condensate through a (spatial)
potential barrier.
