On the explanation of the paramagnetic Meissner effect in superconductor/ferromagnet heterostructures

¹ Wigner Research Centre for Physics, Hungarian Academy of Sciences - Budapest, Hungary
² Division of Molecular Physics, IFM, Linköping University - Linköping, Sweden
³ Max-Planck Institute for Solid State Research - Stuttgart, Germany
⁴ Max Planck Society Outstation at FRM-II - Garching, Germany
⁵ Skobeltsyn Institute of Nuclear Physics, Moscow State University - Moscow, Russia
⁶ Leibniz Institute for Solid State and Materials Research Dresden - Dresden, Germany
⁷ National Research University Higher School of Economics - Moscow, Russia
⁸ Ruhr-Universität Bochum - Bochum, Germany
⁹ Division of Physical Chemistry, Department of Chemistry, Lund University - Lund, Sweden
¹⁰ Helmholtz-Zentrum für Materialien und Energie - Berlin, Germany

Received: 26 July 2016
Accepted: 28 October 2016

Abstract

An increase of the magnetic moment in superconductor/ferromagnet (S/F) bilayers V(40 nm)/F (, Co(3 nm), Ni(3 nm)) was observed using SQUID magnetometry upon cooling below the superconducting transition temperature T_C in magnetic fields of 10 Oe to 50 Oe applied parallel to the sample surface. A similar increase, often called the paramagnetic Meissner effect (PME), was observed before in various superconductors and superconductor/ferromagnet systems. To explain the PME effect in the presented S/F bilayers a model based on a row of vortices located at the S/F interface is proposed. According to the model the magnetic moment induced below T_C consists of the paramagnetic contribution of the vortex cores and the diamagnetic contribution of the vortex-free region of the S layer. Since the thickness of the S layer is found to be 3–4 times less than the magnetic-field penetration depth, this latter diamagnetic contribution is negligible. The model correctly accounts for the sign, the approximate magnitude and the field dependence of the paramagnetic and the Meissner contributions of the induced magnetic moment upon passing the superconducting transition of a ferromagnet/superconductor bilayer.