Magnetization dynamics in proximity-coupled superconductor/ferromagnet/superconductor multilayers

TL;DR

This study investigates magnetization dynamics in superconductor/ferromagnet/superconductor multilayers, revealing a significant, long-range shift in ferromagnetic resonance frequencies due to proximity effects, with potential applications in superconducting magnonics.

Contribution

It demonstrates a robust, long-range proximity-induced magnetic anisotropy in multilayers, leading to the highest reported anisotropy and resonance frequency in ferromagnetic films.

Findings

Resonance frequency shifts to higher values due to superconducting proximity.

Proximity-induced anisotropies grow with ferromagnetic layer thickness.

Achieved the highest anisotropy and resonance frequency in such structures.

Abstract

In this work, magnetization dynamics is studied in superconductor/ferromagnet/superconductor three-layered films in a wide frequency, field, and temperature ranges using the broad-band ferromagnetic resonance measurement technique. It is shown that in presence of both superconducting layers and of superconducting proximity at both superconductor/ferromagnet interfaces a massive shift of the ferromagnetic resonance to higher frequencies emerges. The phenomenon is robust and essentially long-range: it has been observed for a set of samples with the thickness of ferromagnetic layer in the range from tens up to hundreds of nanometers. The resonance frequency shift is characterized by proximity-induced magnetic anisotropies: by the positive in-plane uniaxial anisotropy and by the drop of magnetization. The shift and the corresponding uniaxial anisotropy grow with the thickness of the ferromagnetic layer. For instance, the anisotropy reaches 0.27~T in experiment for a sample with 350~nm thick ferromagnetic layer, and about 0.4~T in predictions, which makes it a ferromagnetic film structure with the highest anisotropy and the highest natural resonance frequency ever reported. Various scenarios for the superconductivity-induced magnetic anisotropy are discussed. As a result, the origin of the phenomenon remains unclear. Application of the proximity-induced anisotropies in superconducting magnonics is proposed as a way for manipulations with a spin-wave spectrum.