Magnetism in Mn-doped ZnO bulk samples prepared by solid state reaction

Contrasting magnetic properties were obtained from bulk Mn-doped ZnO synthesized under different processing conditions. While a ferrimagnetic phase transition was observable in a ${\mathrm{Zn}}_{\text{0.95}}{\mathrm{Mn}}_{\text{0.05}}\mathrm{O}$ sample processed at 1170 K, no such transition was found for a sample with the same composition processed at 1370 K. The detailed magnetic, structural, and spectroscopic studies of these two samples have revealed that the ferrimagnetic transition in the former sample is attributable to the secondary phase, $(\mathrm{Mn},\mathrm{Zn}){\mathrm{Mn}}_2{\mathrm{O}}_4,$ in the system. For the latter sample processed at higher temperature, no secondary phase was detected and the major feature of the system remained paramagnetic down to 4 K. The implication of the present results for Mn-doped ZnO thin films is discussed.