  We investigate controlled phase separation of a binary Bose-Einstein
condensate (BEC) in the proximity of mixed-spin-channel Feshbach resonance in
the |F = 1, mF = +1> and |F = 2,mF = -1> states of 87Rb at a magnetic field of
9.10 G. Phase separation occurs on the lower magnetic-field side of the
Feshbach resonance while the two components overlap on the higher
magnetic-field side. The Feshbach resonance curve of the scattering length is
obtained from the shape of the atomic cloud by comparison with the numerical
analysis of coupled Gross-Pitaevskii equations.
