Paramagnetic relaxation and wohlleben effect in field-cooled nb thin films

The “Wohlleben effect” (paramagnetic Meissner effect) is found in uniform applied magnetic fields only above a threshold value (Formula presented) for field-cooled Nb films of thickness less than 1000 Å. The initial diamagnetic magnetization observed upon field cooling to fixed temperatures just below (Formula presented) gives way to a logarithmic time relaxation toward paramagnetic values comparable to the critical state magnetization over a period of several hours (normalized rate (Formula presented) implying that the development of the paramagnetic state is moderated by fast flux creep processes. Small field gradients ≈10–20 mOe/cm are found to influence the occurrence of the effect for applied fields (Formula presented)