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. 2020 May 18;10(32):18687-18693.
doi: 10.1039/d0ra02220a. eCollection 2020 May 14.

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

Huan Liu  1 , Gongping Li  1 , Dejun E  1 , Nannan Xu  2 , Qiaolu Lin  1 , Xudong Gao  1 , Changlin Lan  1 , Jingsheng Chen  3 , Canglong Wang  2 , Xuwen Zhan  1 , Kai Zhang  4
Affiliations

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

Huan Liu et al. RSC Adv. .

Abstract

Room temperature ferromagnetism (RTFM) was observed in unirradiated rutile TiO2 single crystals prepared by the floating zone method due to oxygen vacancy (VO) defects. D-D neutrons mainly collide elastically with TiO2, producing VO, titanium vacancies (VTi) 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 (Ms) 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. VO 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 VTi induces a magnetic moment of ∼4 μ B. Combining experimental and theoretical results, increases in VO concentration lead to Ms increases; more VO combine with electrons to form F+, inducing a smaller magnetic moment. VO and VTi play a key role and Ms changes accordingly with larger fluence. VO, F+ and VTi are the most likely origins of RTFM.

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Conflict of interest statement

There are no conflicts to declare.

Figures

Fig. 1
Fig. 1. XRD patterns; (a) (002) peak and (b) drawing of partial enlargement of TiO2 before and after neutron irradiation.
Fig. 2
Fig. 2. Raman spectra of TiO2 before and after neutron irradiation.
Fig. 3
Fig. 3. M–H curves of TiO2 before and after neutron irradiation.
Fig. 4
Fig. 4. XPS spectra of (a) raw and (b) 2 × 109 n cm−2 TiO2 samples.
Fig. 5
Fig. 5. (a) Raw PL spectra of TiO2 before and after neutron irradiation and (b) normalized PL spectra for 2 × 109 n cm−2.
Fig. 6
Fig. 6. Spin-polarized total and partial DOS of (a) pure TiO2, (b) the TiO2 supercell with one VO, (c) the TiO2 supercell with F+, (d) the TiO2 supercell with VTi, (e) the TiO2 supercell with V−Ti, (f) the TiO2 supercell with Ti3+, (g) the TiO2 supercell with Oi, (h) the TiO2 supercell with Tii, (i) the TiO2 supercell with VO–Ti3+.
Fig. 7
Fig. 7. The PDOS of (a) Ti of VO, (b) Ti of F+, (c) O of VTi, (d) O of V−Ti.
Fig. 8
Fig. 8. ESR spectra of TiO2 before and after neutron irradiation.
Fig. 9
Fig. 9. UV-Vis spectra of TiO2 before and after neutron irradiation.
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