Dynamically generated spin-interactions and nutational spin inertia in normal metal-ferromagnet heterostructures

TL;DR

This paper investigates how dynamical RKKY interactions induce anisotropic spin nutation in ferromagnet-normal metal heterostructures, leading to a tunable third ferromagnetic resonance that signals nutational spin dynamics.

Contribution

It introduces the concept of anisotropic spin nutation due to dynamical RKKY interactions and predicts a tunable third ferromagnetic resonance as a signature.

Findings

Spin nutation is anisotropic in ferromagnet heterostructures.

A third ferromagnetic resonance mode is predicted due to nutation.

Resonance frequency can be tuned with an external magnetic field.

Abstract

We consider the spin dynamics of a normal metal-ferromagnet heterostructure, with emphasis on spin-nutation terms arising from a dynamical Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction. We find that the spin-nutation term is anisotropic in spin space due to the broken time-reversal symmetry of the ferromagnet. This contrasts with what one obtains in the paramagnetic state, where the nutation term is isotropic in spin space. We compute the effects this has on the magnetization dynamics derived from a Landau-Lifshitz-Gilbert equation. In particular, due to broken time-reversal symmetry, we predict a third ferromagnetic resonance due to nutational spin dynamics. This resonance frequency is tunable by applying an external magnetic field. We propose this as a strong indicator for the existence of nutation in spin systems.