Evidence for two vortex specites in niobium films in parallel fields

摘要

Using torque magnetometry we have investigated the transverse magnetization in niobium thin films of thickness 120 nm and 12. #mu# m at different angles #theta# between applied field and main surface of the films. Torque measurements at angles 10 deg >= #theta# >= 2 deg in the 120 nm thick film reveal nearly temperature independent anomalies in the magnetization at matching fields which are compatilbe with the rearrangement of vortices in one or two inplane rows, while in the 1.2 #mu# m thick film these anomalies are not observed. At very small angles #theta# < 0.5 deg , the matching effects surprisingly vanish. At these small angles and for both films, the observed behavior can be understood assuming that vortices due to perpendicular field component experience a pinning barrier of geometrical origin for flux entry or exit. These results indicate the presence of two flux-line-lattices, parallel and perpendicular to the main surface of the film, in both Nb-films.