Orientation of vortices in a superconducting thin film: Quantitative comparison of spin-polarized neutron reflectivity and magnetization

We present a quantitative comparison of the magnetization measured by spin-polarized neutron reflectivity (SPNR) and dc magnetometry on a 1370 Å-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 the vortex magnetic field out of the film plane as the applied field is reduced. 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; thus combining the two techniques allows one to distinguish two components of magnetization in a thin film.