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

Abstract

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) 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.

Defect-induced room temperature ferromagnetism in Fe and Na co-doped ZnO nanoparticles

“…A lot of further researches concerning their ferromagnetism mechanisms and the impact factors have been carried out, and various debates are never scarce. In recent research works, additional defects such as oxygen vacancies or H interstitials were proved to play an important role in establishing or enhancing the magnetic couplings both in oxides compound [13][14][15] and doping compounds [16][17][18]. Many types of oxide semiconductors such as HfO 2 , CeO 2 , CaO, etc.…”

Mechanism of multi-defect induced ferromagnetism in undoped rutile TiO2

“…[2][3][4][5][6][7]9 On the other hand, first-principles calculations indicate that local magnetic moments are due to cation vacancies in CaO, 10 HfO 2 , 11 ZnO, 12 SnO 2 , 13 and TiO 2 14 while V O cannot induce local moments. Both experimental evidences [2][3][4][5][6][7][8][9] and theoretical studies [10][11][12][13][14] revealed that the ferromagnetism is induced by intrinsic defects in undoped oxides. However, whether cation vacancy or anion vacancy defect contributes to the RT ferromagnetism is still controversial.…”

“…So far, "d 0 " ferromagnetism has been observed in undoped TiO 2 , [2][3][4][5][6] In 2 O 3 , 2,7 ZnO, 7,8 and SnO 2 7,9 films, nanoparticle and nanoribbons. Most experimental evidences indicate that the RT ferromagnetism in these undoped oxides is induced by V O .…”

“…Following that, RT ferromagnetism is reported in undoped TiO 2 films 3 and single crystals 4 in 2009, bulk powder in 2011 5 and nanoribbons in 2013 6 successively. In these experiments the similar evidences are observed, the local moments in undoped TiO 2 single crystal 4 and bulk powder 5 are attributed to Ti 3þ -V O defect complexes while the RT ferromagnetism in undoped TiO 2 films 3 and nanoribbons 6 are reported to be induced by V O . Meanwhile, Santara et al 6 noted that the precursor TiO 2 powder did not show any trace of ferromagnetism, despite the presence of a large concentration of V O .…”

Transforming from paramagnetism to room temperature ferromagnetism in CuO by ball milling

“…Recently, Singhal et al also reported the RTFM in pristine anatase TiO 2 paramagnetic bulk through extended hydrogenation. 25 The defect complexes of Ti 3+ -V O are clearly identified in hydrogenated TiO 2 and they elucidate that the factors of Ti 3d-O 2p hybridization, F + centers, and oxygen vacancy assisted fragmentation of grains, compositely contribute to the ferromagnetic ordering. The F-center exchange mechanism has been used to explain observed FM, which also may explain the observed FM in our case.…”