Room temperature ferromagnetism in D-D neutron irradiated rutile TiO 2 single crystals.

Room temperature ferromagnetism (RTFM) was observed in unirradiated rutile TiO 2 single crystals prepared by the floating zone method due to oxygen vacancy (V O ) defects. D-D neutrons mainly collide elastically with TiO 2 , producing V O , titanium vacancies (V Ti ) and other point defects; the density and kind of defect is related to the neutron irradiation fluence. D-D neutron irradiation is used to regulate the concentration and type of defect, avoiding impurity elements. As the irradiation fluence increases, the saturation magnetization (M s ) first increases, then decreases and then increases. To verify the origin of RTFM, the CASTEP module was used to calculate the magnetic and structural properties of point defects in TiO 2 . V O induces a 2.39 μ B magnetic moment, Ti 3+ and F + induce 1.28 μ B and 1.70 μ B magnetic moments, respectively, while V Ti induces a magnetic moment of ∼4 μ B . Combining experimental and theoretical results, increases in V O concentration lead to M s increases; more V O combine with electrons to form F + , inducing a smaller magnetic moment. V O and V Ti play a key role and M s changes accordingly with larger fluence. V O , F + and V Ti are the most likely origins of RTFM.