  We study the phenomenon of neutrino spin-flavor oscillations due to solar
magnetic fields. This allows us to examine how significantly the electron
neutrinos produced in the solar interior undergo a resonant spin-flavor
conversion. We construct analytical models for the solar magnetic field in all
the three regions of the Sun. Neutrino spin-flavor oscillations in these
magnetic fields are examined by studying the level crossing phenomenon and
comparing the two cases of zero and non-zero vacuum mixing respectively.
Results from the Borexino experiment are used to place an upper limit on the
magnetic field in the solar core. Related phenomena such as effects of matter
on neutrino spin transitions and differences between Dirac and Majorana
transitions in the solar magnetic fields are also discussed.
