  It remains a challenge to independently manipulate the magnetic dipolar and
the spin-exchange interactions, which are entangled in many spin systems,
particularly in spin-1 Bose-Einstein condensates. For this purpose, we put
forward a sequence of rf pulses and the periodic dynamical decoupling sequence
of optical Feshbach resonance pulses to control the dipolar and the
spin-exchange interactions, respectively. Our analytic results and the
numerical simulations demonstrate that either of the two interactions can be
suppressed to make the other dominate the spin dynamics; furthermore, both of
the interactions can be simultaneously suppressed to realize
spinor-condensate-based magnetometers with a higher sensitivity. This
manipulation method may find its wide applications in magnetic resonance and
spintronics.
