We report results of the first muon-spin rotation measurements performed on the low carrier density ferromagnet EuB6. The ferromagnetic state is reached via two magnetic transitions at Tm=15.5 K and T c=12.6 K. Two distinct components are resolved in the muon data, one oscillatory and one non-oscillatory, which arise from different types of magnetic environment, and we have followed the temperature dependence of these components in detail. These results provide evidence for magnetic phase separation and can be interpreted in terms of the gradual coalescing of magnetic polarons.

We report the results of transverse field (TF) and zero-field (ZF) μSR measurements on the hexaboride system EuxCa1-xB6. EuB6 is a semimetallic ferromagnet that magnetically orders via two transitions at Tm≈15K and Tc≈12K, with colossal magnetoresistance accompanying the higher temperature transition. New TF μSR 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, xp=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. © 2005 Elsevier B.V. All rights reserved.