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Percolation and Colossal Magnetoresistance in Eu-based Hexaborides

G. A. Wigger·C. Beeli·E. Felder·H. R. Ott·A. D. Bianchi·Z. Fisk
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Abstract

Upon substituting Ca for Eu in the local-moment ferromagnet EuB$_6$, the Curie temperature $T_C$ decreases substantially with increasing dilution of the magnetic sublattice and is completely suppressed for $x$ $\leq$ 0.3. The Ca substitution leads to significant changes of the electronic properties across the Eu$_x$Ca$_{1-x}$B$_6$ series. Electron microscopy data for $x$ $\approx$ 0.27 indicate a phase separation into Eu- and Ca-rich clusters of 5 to 10 nm diameter, leading to percolation-type phenomena in the electrical transport properties. The related critical concentration $x_p$ is approximately 0.3. For $x$ $\approx$ 0.27, we observe colossal negative magnetoresistance effects at low temperatures, similar in magnitude as those reported for manganese oxides.

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G. A. Wigger, C. Beeli, E. Felder, H. R. Ott, A. D. Bianchi, Z. Fisk. 2004-04-23. Percolation and Colossal Magnetoresistance in Eu-based Hexaborides. https://doi.org/10.1103/physrevlett.93.147203

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