μSR studies of the hexaboride system EuxCa1-xB6

We report the results of transverse field (TF) and zero-field (ZF) mu SR measurements on the hexaboride system EuxCa1-xB6. EuB6 is a semimetallic ferromagnet that magnetically orders via two transitions at T-m approximate to 15 K and T-c approximate to 12 K, with colossal magnetoresistance accompanying the higher temperature transition. New TF mu SR measurements on EuB6 allow us to follow the temperature evolution of the local magnetic field distribution through the two magnetic transitions. Substitution of Ca for Eu dilutes the magnetic sublattice, causing a substantial suppression of the transition temperature, with the transition completely removed when the doping level approaches the three-dimensional site percolation limit, x(p) = 0.31. ZF experiments on doped samples, 0.35 <= x <= 1, enable a sensitive local-probe exploration of the order and dynamics across the phase diagram. (c) 2005 Elsevier B.V. All rights reserved.