Mn-doped TiO2 nanoparticles were synthesized by sol-gel method. Incorporation of Mn shifts the diffraction peak of TiO2 to lower angle. The position and width of the Raman peak and photoluminescence intensity of the doped nanoparticles varies with oxygen vacancy and Mn doping level. The electron spin resonance spectra of the Mn-doped TiO2 had peaks at g = 1.99 and 4.39, characteristic of the Mn2+ state. Reduction in the emission intensity, on Mn doping, was owing to the increase of non-radiative oxygen vacancy centers. Mn-doped TiO2, with 2%Mn, exhibited ferromagnetic ordering at low applied field. The paramagnetic contribution increased as the Mn loading increased to 4 and 6%. Temperature-dependent magnetic measurements revealed a small kink in the ZFC curve at about 40K, characteristic of Mn3O4. The ferromagnetic ordering was possibly due to the interaction of the neighboring Mn2+ ions via oxygen vacancy (F+ center). Increases in Mn concentration increased the fraction of Mn3O4 phase and thereby increased the paramagnetic ordering.

Oxygen Vacancy and Dopant Concentration Dependent Magnetic Properties of Mn Doped TiO2 Nanoparticle. Choudhury, B., Choudhury, A.: Current Applied Physics, 2013, 13[6], 1025-31