Phenomenological Model of Longitudinal Spin Fluctuations in Itinerant Antiferromagnets

TL;DR

This paper develops a phenomenological model for longitudinal spin fluctuations in isotropic itinerant antiferromagnets, highlighting the effects of spin anharmonicity and mode coupling on the fluctuation spectrum.

Contribution

It introduces a novel phenomenological approach accounting for spin anharmonicity and mode coupling in the spectrum of longitudinal spin fluctuations.

Findings

Spectrum includes quasielastic peaks or dips depending on temperature.

Spin fluctuation coupling causes resonances or antiresonances near magnon frequencies.

The model explains non-propagating longitudinal excitations in antiferromagnets.

Abstract

We present the phenomenological analysis of the spectrum of longitudinal spin fluctuations in isotropic itinerant electron antiferromagnets with account of spin anharmonicity giving rise to coupling of transverse and longitudinal normal modes. The spectrum consists of a quasielastic part forming a central peak or a dip, depending on temperature and the Landau relaxation rate. Effects of spin fluctuation coupling also give rise to an inelastic part of the spectrum which has a form of resonances or antiresonances near the magnon frequencies related to non-propagating longitudinal excitations.