  We present a quantitative comparison of the magnetization measured by
spin-polarized neutron reflectivity (SPNR) and DC magnetometry on a 1370 \AA\
-thick Nb superconducting film. As a function of magnetic field applied in the
film plane, SPNR exhibits reversible behavior whereas the DC magnetization
shows substantial hysteresis. The difference between these measurements is
attributed to a rotation of vortex magnetic field out of the film plane as the
applied field is reduced. Since SPNR measures only the magnetization parallel
to the film plane whereas DC magnetization is strongly influenced by the
perpendicular component of magnetization when there is a slight sample tilt,
combining the two techniques allows one to distinguish two components of
magnetization in a thin film.
