Interaction of Josephson and magnetic oscillations in Josephson tunnel junctions with a ferromagnetic layer

TL;DR

This paper investigates the coupled dynamics of superconducting phase difference and magnetization in Josephson junctions with ferromagnetic layers, revealing how magnetic interactions modify electrical characteristics and resonance behaviors.

Contribution

It derives equations for coupled Josephson and magnetic dynamics, analyzing their impact on current-voltage characteristics and microwave absorption in SFIFS junctions.

Findings

Modified Fiske steps due to magnetic effects

Appearance of new peaks in I-V curves related to magnetic resonance

Distinct power absorption features for magnetic and plasma resonances

Abstract

We study the dynamics of Josephson junctions with a thin ferromagnetic layer F [superconductor-ferromagnet-insulator-ferromagnet-superconductor (SFIFS) junctions]. In such junctions, the phase difference $\phi$ of the superconductors and magnetization $M$ in the F layer are two dynamic parameters coupled to each other. We derive equations describing the dynamics of these two parameters and formulate the conditions of validity. The coupled Josephson plasma waves and oscillations of the magnetization $M$ affect the form of the current-voltage ($I$-$V$) characteristics in the presence of a weak magnetic field (Fiske steps). We calculate the modified Fiske steps and show that the magnetic degree of freedom not only changes the form of the Fiske steps but also the overall view of the $I$-$V$ curve (new peaks related to the magnetic resonance appear). The $I$-$V$ characteristics are shown for different lengths of the junction including those which correspond to the current experimental situation. We also calculate the power $P$ absorbed in the system if a microwave radiation with an ac in-plane magnetic field is applied (magnetic resonance). The derived formula for the power $P$ essentially differs from the one which describes the power absorption in an isolated ferromagnetic film. In particular, this formula describes the peaks related to the excitation of standing plasma waves as well as the peak associated with the magnetic resonance.