Below the Kondo temperature the heavy Fermion compound YbRh$_{ 2}$Si$_{ 2}$ shows a well defined Electron Spin Resonance (ESR) with local Yb$^{ 3+}$ 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 Yb$^{ 3+}$ in YPd$_3$:Yb. The ESR lineshape is investigated regarding contributions from itinerant centers. From the ESR of monoisotopic $^{ 174}$YbRh$_{ 2}$Si$_{ 2}$ we could exclude unresolved hyperfine contributions to the lineshape.
Categories: cond-mat.str-el