Signatures of Surface Magnetic Disorder in Niobium Films

We present our studies on the evolution of the normal and superconducting properties with thickness of thin Nb films with a low level of non-magnetic disorder (k _F l ≈ 150 for the thickest film in the set). The analysis of the superconducting behavior points to the presence of magnetic moments, hidden in the native oxide on the surface of Nb films. Using the Abrikosov-Gorkov theory, we obtain the density of surface magnetic moments of 10 ¹³ cm ^-2 , which is in agreement with the previously reported data for Nb films.