Abstract
We investigated the upper critical magnetic field of a superconductor-ferromagnet (S/F) bilayer of Nb/ and a Nb film (as reference). We obtained the dependence of and (perpendicular and parallel to the film plane, respectively) on the temperature by measurements of the resistive transitions and the dependence on the inclination angle of the applied field to the film plane, by nonresonant microwave absorption. Over a wide range, and show the temperature dependence predicted by the Ginzburg-Landau theory. At low temperatures and close to the critical temperature, deviations are observed. While of the Nb film follows the Tinkham prediction for thin superconducting films, the Nb/-bilayer data exhibit deviations when approaches zero. We attribute this finding to the additional anisotropy induced by the quasi-one-dimensional Fulde-Ferrell-Larkin-Ovchinnikov (FFLO)-like state and propose a new vortex structure in S/F bilayers, adopting the segmentation approach from high-temperature superconductors.
- Received 16 September 2015
- Revised 31 March 2016
DOI:https://doi.org/10.1103/PhysRevB.93.184501
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