  We report that thin films of a prototype topological insulator,
Bi$_{2}$Se$_{3}$, can be epitaxially grown onto the (0001) surface of
BaFe$_{12}$O$_{19}$(BaM), a magnetic insulator with high Curie temperature and
large perpendicular anisotropy. In the Bi$_2$Se$_3$ thin films grown on
non-magnetic substrates, classic weak antilocalization (WAL) is manifested as
cusp-shaped positive magnetoresistance (MR) in perpendicular magnetic fields
and parabola-shaped positive MR in parallel fields, whereas in
Bi$_{2}$Se$_{3}$/BaM heterostructures the low field MR is parabola-shaped,
which is positive in perpendicular fields and negative in parallel fields. The
magnetic field and temperature dependence of the MR is explained as a
consequence of the suppression of WAL due to strong magnetic interactions at
the Bi$_{2}$Se$_{3}$/BaM interface.
