  The majority of solar-type stars reside in multiple systems, especially
binaries. They form in dense cores of molecular clouds that are observed to be
significantly magnetized. Our previous study shows that magnetic braking can
tighten the binary separation during the protostellar mass accretion phase by
removing the angular momentum of the accreting material. Recent numerical
calculations of single star formation have shown that misalignment between the
magnetic field and rotation axis may weaken both magnetic braking and the
associated magnetically driven outflows. These two effects allow for disk
formation even in strongly magnetized cores. Here we investigate the effects of
magnetic field misalignment on the properties of protobinaries. Somewhat
surprisingly, the misaligned magnetic field is more efficient at tightening the
binary orbit compared to the aligned field. The main reason is that the
misalignment weakens the magnetically-driven outflow, which allows more
material to accrete onto the binary. Even though the specific angular momentum
of this inner material is higher than in the aligned case, it is insufficient
to compensate for the additional mass. A corollary of this result is that a
weaker field is required to achieve the same degree of inward migration when
the field is tilted relative to the rotation axis. Large field misalignment
also helps to produce rotationally-supported circumbinary disks even for
relatively strong magnetic fields, by weakening the magnetically-dominated
structure close to the binary. Our result may provide an explanation for the
circumbinary disks detected in recent SMA and ALMA observations.
