Evidence of defect-induced ferromagnetism and its switch action in pristine bulk TiO2

In this work, we demonstrate that room temperature ferromagnetism can be induced in pristine anatase TiO2 paramagnetic bulk powder through extended hydrogenation. Defect complexes, Ti3+-V-O (Ti3+ ions accompanied by oxygen vacancies) are clearly identified in hydrogenated TiO2 by combining x-ray diffraction and photoemission spectroscopy. The observed ferromagnetic ordering is reversible that can be switched between on and off by inducing or removing, respectively, these defect complex. We convincingly elucidate that the factors (i) Ti 3d-O 2p hybridization (iii) F+ centers (the electrons in singly occupied oxygen vacancies), and (iii) oxygen vacancy assisted fragmentation of grains, compositely contribute to the ferromagnetic ordering. (C) 2011 American Institute of Physics. [doi:10.1063/1.3562328]