Intrinsic paramagnetism and aggregation of manganese dopants in   SrTiO$_3$
  Using local-probe magnetic-characterization techniques of muon spin relaxation ($\mu$SR) and electron spin resonance (ESR) we have investigated the Mn-induced magnetism of the wide-bandgap perovskite SrTiO$_3$. Our results clearly demonstrate that this diluted magnetic oxide (DMO) remains paramagnetic down to low temperatures for both doping cases, i.e., when Mn substitutes for Sr or Ti. In addition, both experimental techniques have unveiled that the distribution of individual Mn$^{2+}$ and Mn$^{4+}$ ions is nonrandom, as these ions partially aggregate into nanosized clusters. 
Andrej Zorko, Matej Pregelj, Hubertus Luetkens, Anna-Karin Axelsson,   Matjaz Valant
cond-mat.str-el cond-mat.mtrl-sci