Effects of temperature on the ferromagnetism of Mn-doped ZnO nanoparticles and Mn-related Raman vibration

Mn-doped ZnO nanoparticles were synthesized by a rheological phase-reaction-precursor method and the thermal decomposition of the oxalate precursors was studied by thermogravimetry and differential thermal analysis in air. The Mn-doped ZnO obtained at lower temperature crystallizes in a wurtzite structure and a new phase appears at higher temperature. The lattice parameters of Zn1-xMnxO (0.09 <= x <= 0.1) increase gradually with increasing temperature up to 650 degrees C and then decrease. X-ray photoelectron spectroscopy indicates that there are different Mn valence bonds in Mn-doped ZnO nanoparticles. Furthermore, two additional Raman peaks were observed. One peak is considered to have an origin related to the incorporation of Mn ions into the Zn site of the ZnO lattice; the other may be attributed to the ZnMnO3 phase. Magnetization measurements under field cooling conditions reveal that the Zn1-xMnxO nanoparticles exhibit ferromagnetic behaviour, and the Curie temperatures of some samples are above room temperature. The difference of the ferromagnetic properties of the Mn-doped ZnO nanoparticles is primarily attributed to the Mn2+ content.