Electron spin resonance of Eu2+ in the Eu doped clathrate Ba6Ge25

We report electron spin resonance (ESR) investigations of the clathrate compound Ba6-xEuxGe25 (x=0.03-0.4) which exhibits a temperature induced, two-step reconstructive structure transformation at temperatures between 185 K and 223 K. The linewidth of the Eu2+ ESR proves to be sensitive to the transformation. Another anomaly in the temperature dependence of the linewidth is found near T=60 K which points towards another possible structural transition. Both anomalies seen in the ESR linewidth are not sensitive to the Eu content in contrast to the strong Eu-concentration dependence of transport properties. © EDP Sciences, Società Italiana di Fisica, Springer-Verlag 2005.