paper

Percolation and Colossal Magnetoresistance in Eu-based Hexaborides

arXiv:cond-mat/0404570 · doi:10.1103/PhysRevLett.93.147203

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.

4 pages, 5 figures, submitted to PRL