  In the mixture of ultracold spin-1 atoms of two different species A and B
(e.g., $^{23}$Na (A) and $^{87}$Rb (B)), inter-species singlet-pairing process
${\rm A}_{+1}+{\rm B}_{-1}\rightleftharpoons {\rm A}_{-1}+{\rm B}_{+1}$, can be
induced by the spin-dependent inter-atomic interaction, where subscript $\pm 1$
denotes the magnetic quantum number. Nevertheless, one cannot isolate this
process from other spin-changing processes by tuning the bias real magnetic
field. As a result, so far the singlet-pairing process have not been clearly
observed in the experiments, and the measurement of the corresponding
interaction strength becomes difficult. In this work we propose to control the
singlet-pairing process via combining the real magnetic field and a
laser-induced species-dependent synthetic magnetic field. With our approach one
can significantly enhance this process and simultaneously supperess all other
spin-changing processes. We illustrate our approach for both a confined
two-atom system and a binary mixture of spinor Bose-Einstein condensates. Our
control scheme is helpful for the precise measurement of the weakly
singlet-pairing interaction strength and the entanglement generation of two
different atoms.
