On the local and itinerant properties of the ESR in YbRh2Si2

Below the Kondo temperature the heavy Fermion compound YbRh2Si2 shows a well defined electron spin resonance (ESR) with local Yb3+ properties. We report a detailed analysis of the ESR intensity which gives information on the number of ESR active centers relative to the ESR of well localized Yb3+ in YPd3:Yb. The ESR lineshape is investigated regarding contributions from itinerant centers. From the ESR of monoisotopic 174YbRh2Si2 we could exclude unresolved hyperfine contributions to the lineshape.