Electron spin resonance of Eu<Superscript>2 +</Superscript> in the Eu doped clathrate Ba<Subscript>6</Subscript>Ge<Subscript>25</Subscript>

We report electron spin resonance (ESR) investigations of the clathrate compound Ba<Subscript>6-x</Subscript>Eu<Subscript>x</Subscript>Ge<Subscript>25</Sub script> (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 Eu<Superscript>2+</Superscript> 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. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005