muSR study of the percolation process in a new dilute magnetic semiconductor series

Doping electric charges into semiconductors drastically changes their electronic properties. Whether dopinga small number of magnetic spins
results in ferromagnetism in nonmagnetic semiconductors has been a vigorously debated topic for more than 30 years, largely due to the lack of evidence for an intrinsicferromagnetic transition in so-called dilute magnetic semiconductors. However, we have just discovered an intrinsic ferromagnetic transition with unambiguous evidence in the semiconductor (Sr1-xRx)SiO3 doped with rare-earth magnetic ions R, which entered the Sr site in the lattice. Surprisingly, partial ferromagnetic behavior can be induced at an ultralow doping concentration, with the transition temperature obeying an exponential function with the doping concentration. At doping higher than 0.1%, the transition temperature is almost independent of the doping concentration and shows evidence of percolation into a long-range orde. In the sample doped with 5%Dy, long-range ferromagnetic order, which was never witnessed in any previous dilute magnetic semiconductors, was clearly observed in muon spin spectroscopy. We have also obtained other evidence suggesting a magnetic polaron picture for the unexpected magnetism. It is of ultimate interest to reveal the percolation process in this unexpected dilute magnet. We thus propose to investigate the percolation process using the muon beam line at ARGUS.