Crossing fields in thin films of isotropic superconductors

We study magnetic flux cutting effects by imaging the vortex dynamics in Nb films of different thickness in the crossing in-plane (H$_{\mathrm{\vert \vert }})$ and normal fields. For H$_{\mathrm{\vert \vert }}=$1 kOe the motion of the normal vortices in a 200 nm film is found to be anisotropic. At T\textgreater T$_{\mathrm{c}}$/2 we observe a delay in the vortex propagation across H$_{\mathrm{\vert \vert }}$. At T\textless T$_{\mathrm{c}}$/2, when thermomagnetic instabilities occur, the vortex dendrites tilt perpendicular to the in-plane field direction. In a 100 nm film, the normal flux dynamics is isotropic and independent of H$_{\mathrm{\vert \vert }}$. Our calculations of the thermodynamic potential for the in-plane vortices predict their existence at H$_{\mathrm{\vert \vert }}=$1 kOe only in the 200 nm film. In the 100 nm sample, H$_{\mathrm{\vert \vert \thinspace }}$monotonously changes through the film thickness. Therefore, the observed delay of the normal flux motion across H$_{\mathrm{\vert \vert }}$ in the thicker film is due to the vortex cutting-reconnection of the normal and in-plane vortices. The enhanced pinning potential for motion across H$_{\mathrm{\vert \vert }}$ explains also the tilt of the dendrite branches at T\textless T$_{\mathrm{c}}$/2.