Room temperature ferromagnetism in D–D neutron irradiated rutile TiO2 single crystals

Abstract

Room temperature ferromagnetism (RTFM) was observed in unirradiated rutile TiO₂ single crystals prepared by the floating zone method due to oxygen vacancy (V_O) defects. D–D neutrons mainly collide elastically with TiO₂, 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 TiO₂. V_O induces a 2.39 μ_B magnetic moment, Ti³⁺ 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.