Excitation of Spin Waves in Superconducting Ferromagnets

TL;DR

This paper provides a theoretical analysis of spin wave propagation in superconducting ferromagnets, identifying conditions for singularities in impedance and the existence of counter-propagating spin waves with potential negative group velocity.

Contribution

It introduces a theoretical framework for understanding spin wave behavior in superconducting ferromagnets, including impedance singularities and conditions for negative group velocity.

Findings

Identified frequencies with impedance and power absorption singularities.

Discovered a frequency interval with two propagating spin waves of the same polarization.

Found conditions under which one spin wave has negative group velocity.

Abstract

This Letter presents a theoretical analysis of propagation of spin waves in a superconducting ferromagnet. The surface impedance was calculated for the case when the magnetization is normal to the sample surface. We found the frequencies at which the impedance and the power absorption have singularities related to the spin wave propagation, and determined the form of these singularities. With a suitable choice of parameters, there is a frequency interval in which two propagating spin waves of the same circular polarization are generated, one of them having a negative group velocity.