Relevance of ferromagnetic correlations for the Electron Spin Resonance in Kondo lattice systems

TL;DR

This paper investigates how ferromagnetic correlations influence Electron Spin Resonance (ESR) signals in Kondo lattice systems, revealing that ESR presence correlates with ferromagnetic fluctuations rather than antiferromagnetic or quantum critical behavior.

Contribution

It demonstrates that ESR signals in Kondo lattices are linked to ferromagnetic fluctuations, providing new insights into spin dynamics and the conditions for ESR observability in these systems.

Findings

ESR observed in ferromagnetic CeRuPO and YbRh

ESR absent in antiferromagnetic CeOsPO and other compounds

ESR presence correlates with ferromagnetic fluctuations

Abstract

Electron Spin Resonance (ESR) measurements of the ferromagnetic Kondo lattice system CeRuPO show a well defined ESR signal which is related to the magnetic properties of the Ce3+ moment. In contrast, no ESR signal could be observed in the antiferromagnetic homologue CeOsPO. Additionally, we detect an ESR signal in a further ferromagnetic Yb compound, YbRh, while it was absent in a number of Ce or Yb intermetallic compounds with dominant antiferromagnetic exchange, independently of the presence of a strong Kondo interaction or the proximity to a (quantum) critical point. Thus, the observation of an ESR signal in a Kondo lattice is neither specific to Yb nor to the proximity of a quantum critical point, but seems to be connected to the presence of ferromagnetic fluctuations. These conclusions not only provide a basic concept to understand the ESR in Kondo lattice systems even well below the Kondo temperature as observed in the heavy fermion metal YbRh2Si2 but point out ESR as a prime method to investigate directly the spin dynamics of the Kondo ion.