Electron spin resonance of the Kondo ion in YbRh2Si2

By means of electron spin resonance (ESR) we investigated the dynamic magnetic properties of the heavy fermion metal YbRh2Si2. This is the first observation of Yb3+-ESR in YbRh2Si 2 being also the first ESR signal of a Kondo ion in a dense Kondo lattice system. Below T = 25 K strongly anisotropic ESR spectra observed in high-quality single crystals demonstrate the existence of local Yb3+ magnetic moments even below a characteristic spin fluctuation temperature derived from thermodynamic properties. © 2003 Elsevier B.V. All rights reserved