Muon spin rotation/relaxation spectroscopy %(supported by magnetization measurements) has been employed to study electron localization around a donor center - the positive muon - in the 3d magnetic spinel semiconductor CdCr2Se4 at temperatures from 2 to 300 K in magnetic fields up to 7 T. A bound state of an electron around a positive muon - a magnetic polaron - is detected far above the ferromagnetic transition up to 300 K. Electron localization into a magnetic polaron occurs due to its strong exchange interaction with the magnetic 3d electrons of local Cr3+ ions, which confines its wave function within R\approx 0.3 nm, allowing significant overlap with both the nearest and next nearest shells of Cr ions.
@article{arxiv.1003.1851,
title = {Bound Magnetic Polarons in the 3d-electron Ferromagnetic Spinel Semiconductor CdCr$_2$Se$_4$},
author = {Vyacheslav G. Storchak and Jess H. Brewer and Peter L. Russo and Scott L. Stubbs and Oleg E. Parfenov and Roger L. Lichti and Tel'man G. Aminov},
journal= {arXiv preprint arXiv:1003.1851},
year = {2015}
}