DC magnetization investigations in Ti1-xMnxO2 nanocrystalline powder

In the present paper, DC magnetization investigation on the insulating nanocrystalline powder samples of Ti1-xMnxO2 (x = 0, 0.05, 0.10, and 0.15) prepared by simple chemical route is reported. Structural measurements revealed phase pure anatase structure of TiO2 when x <= 0.05 and a mixture of anatase and rutile TiO2 along with the signature of Mn3O4 phase for x > 0.05. Magnetic measurements exhibited the presence of ferromagnetic ordering at room temperature in samples having either small fraction of Mn or no Mn at all. This ferromagnetic signature is accompanied with paramagnetic contribution which is found to dominate with increase in Mn concentration. The Ti1-xMnxO2 sample having highest Mn concentration of x = 0.15 showed nearly paramagnetic behavior. However, at low temperatures, additional ferrimagnetic ordering arising due to Mn3O4 (T-C = 42K) is evidenced in the doped samples. Consistent with the XRD investigations, the isofield DC-magnetization measurements under field cooled and zero field cooled (FC-ZFC) histories corroborated the presence of Mn3O4 phase. Also, distinct thermomagnetic irreversibility has been observed above 42 K. These results are suggestive of presence of weak ferromagnetic ordering possibly due to defects related with oxygen vacancies. (C) 2011 Elsevier B.V. All rights reserved.