Upper critical magnetic field and vortex pinning in superconducting/spin glass multilayers

We present a study of the upper critical magnetic field, H-c2, and pinning force, F-p, in superconducting (Nb)/spin glass (CuMn) multilayers. Patterne d samples with different CuMn thicknesses and Mn concentrations were measur ed in both the perpendicular and the parallel magnetic field orientations. The behavior of the perpendicular upper critical field H-c2 perpendicular t o was in agreement with the anisotropic Ginzburg-Landau theory, while the p arallel upper critical field H-c2 parallel to temperature dependence for hi ghly anisotropic samples was nonlinear in the whole investigated temperatur e range. Grain boundary pinning mainly influences the perpendicular critica l current density values independently on the multilayer anisotropy, For pa rallel magnetic field orientation, instead, the intrinsic vortex pinning on CuMn layers was dominant. (C) 1999 Published by Elsevier Science B.V. All rights reserved.