Evolution of Eu2+ spin dynamics in Ba1-xEuxFe2As2

摘要: Single crystals of Ba${}_{1\ensuremath{-}x}$Eu${}_{x}$Fe${}_{2}$As${}_{2}$ were studied by magnetic susceptibility, heat capacity, resistivity, and electron spin resonance (ESR) measurements. Spin-density wave (at ${T}_{\text{SDW}}$) antiferromagnetic ${T}_{N}$) phase transitions mapped as a function $x$. For $x\ensuremath{\ge}0.2$, we found single Eu${}^{2+}$ ESR Dysonian line that presents an isotropic linear increase (Korringa) its linewidth ($\ensuremath{\Delta}H$) above ${T}_{\text{SDW}}$ which systematically decreases with decreasing In contrast, for critical concentration ${x}_{c}$ ($0.10l{x}_{c}l0.20$), $\ensuremath{\Delta}H$ increasing $T$, suggesting distinct relaxation process associate Kondo impurity regime. The Korringa rate suppression towards the Ba-rich compounds is claimed to be due reduction $q$-dependent exchange interaction between $f$ electrons conduction electrons, likely associated localization Fe $d$ electrons. This result may help understanding SDW (that can lead superconductivity) in this class materials.