Dependence of magnetism on the doping level of Zn sub(1-x)Mn sub(x)Te nanoparticles synthesized by a hydrothermal method

Mn-doped ZnTe nanoparticles with various degrees of Mn-doping from 3 at.% to 18 at.% were synthesized by a hydrothermal method. A single-phase zinc-blende-structured sample was obtained only at the Mn-doping level of 3 at.%, while the impurity phase of MnO was present in the samples with higher degrees of Mn-doping. In all of the samples, the Mn valence states were lower than 2+. All samples exhibited both ferromagnetism and paramagnetism. The ferromagnetism is mainly attributable to the overlapping of the bound magnetic polarons and the paramagnetism is mainly caused by the isolated polarons and Mn ions. Samples that were doped with 3 at.% and 6 at.% Mn also exhibited superparamagnetism and antiferromagnetism. The superparamagnetism may have arisen from the presence of some tiny ferromagnetic nanoparticles. The antiferromagnetism is believed to have arisen mainly from the carrier-mediated interaction among Mn ions.