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, $Ti3+–VO$ (⁠$Ti3+$ 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) $Ti3d–O2p$ 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.