Effect of Meissner screening and trapped magnetic flux on magnetization dynamics in thick Nb/Ni80Fe20/Nb trilayers

TL;DR

This study examines how Meissner screening and trapped magnetic flux affect magnetization dynamics in Nb/Ni80Fe20/Nb trilayers, revealing significant shifts and broadening in ferromagnetic resonance spectra below Nb's superconducting transition.

Contribution

It provides new insights into the impact of superconducting screening and flux trapping on ferromagnetic resonance in thick Nb-based heterostructures.

Findings

Zero-frequency line broadening of 5-6 mT observed below Tc

DC resonance field shift of 50 mT to low field

Increased incoherent precession near the Ni80Fe20/Nb interface

Abstract

We investigate the influence of Meissner screening and trapped magnetic flux on magnetization dynamics for a Ni80Fe20 film sandwiched between two thick Nb layers (100 nm) using broadband (5-20 GHz) ferromagnetic resonance (FMR) spectroscopy. Below the superconducting transition Tc of Nb, significant zero-frequency line broadening (5-6 mT) and DC resonance field shift (50 mT) to a low field are both observed if the Nb thickness is comparable to the London penetration depth of Nb films (>= 100 nm). We attribute the observed peculiar behaviors to the increased incoherent precession near the Ni80Fe20/Nb interface and the effectively focused magnetic flux in the middle Ni80Fe20 caused by strong Meissner screening and (defect-)trapped flux of the thick adjacent Nb layers. This explanation is supported by static magnetic properties of the samples and comparison with FMR data on thick Nb/Ni80Fe20 bilayers. Great care should therefore be taken in the analysis of FMR response in ferromagnetic Josephson structures with thick superconductors, a fundamental property for high-frequency device applications of spin-polarized supercurrents.