Study On Magnetic And Optical Properties Of D-D Neutron And ?-ray Irradiation Of TiO₂ And ZnO Single Crystals

Magnetic semiconductors have both of the characteristics of semiconductors and magnetic materials,which can integrate information processing and memory functions on a single component.However,the Curie temperature of magnetic semiconductors is generally much lower than room temperature,which greatly limits the development of magnetic semiconductor devices.TiO₂ and ZnO are the third-generation wide bandgap semiconductor material.They exhibits room temperature ferromagnetism both in the undoped and ions-doped samples,the current understanding of the origin of TiO₂-and ZnO-based room temperature ferromagnetism?RTFM?is still controversial.Therefore,the systematic study of room temperature ferromagnetism of TiO₂-and ZnO-based materials is of great significance for elucidating the magnetic source of dilute magnetic semiconductors and revealing the mechanism of room temperature ferromagnetism.In this paper,the effects of intrinsic defects on room temperature ferromagnetism and optical property of TiO₂and ZnO were studied.The main work and results were summarized as follows:Using D-D neutron irradiated rutile TiO₂,the neutron fluence were 0 ions/cm²,5×10⁹ions/cm²,1×10¹⁰ions/cm²,2.5×10¹⁰ions/cm²,5×10¹⁰ions/cm²,respectively.The changes of sample structural,magnetic and optical properties before and after irradiation were analyzed.Room temperature ferromagnetism?RTFM?was observed in unirradiated rutile TiO₂ single crystal prepared by floating zone method due to oxygen vacancy?V_O?defects.D-D neutron mainly collides elastically with TiO₂,producing V_O,titanium vacancy(V_Ti)and other point defects,the density and kind of defect associated with neutron irradiation fluence.D-D neutron irradiation is used to regulate the defect concentration and types avoiding impurity elements.As the increase of irradiation fluence,saturation magnetization?M_s?first increases,then decreases and then increases.To verify the origin of RTFM,CASTEP module was used to calculate the magnetic and structural properties of point defects in TiO₂.V_O induces 2.39?_B magnetic moment,Ti³⁺and F⁺has 1.28?_B,1.70?_B magnetic moment,while V_Tii introduces a magnetic moment of⁴?_B.Combined with experimental and theoretical results,the increase of V_O concentration leads to the increase of M_s,more V_O combined an electron to form F⁺induce a smaller magnetic moment,then V_O and V_Tii play a key role and M_s changes accordingly in larger fluence.V_O,F⁺and V_Tii are the most likely origin of RTFM.Using D-D neutron irradiated ZnO,the neutron fluence were 0 ions/cm²,5×10⁹ions/cm²,1×10¹⁰ions/cm²,2.5×10¹⁰ions/cm²,respectively.The changes of sample structural,magnetic and optical properties before and after irradiation were analyzed.RTFM was observed in unirradiated ZnO single crystal owing to zinc vacancy(V_Zn)defects.D-D neutron irradiation was used to regulate the defect concentration and types avoiding interference of impurity elements.D-D neutron mainly collides elastically with ZnO single crystals,producing V_Zn,V_O and other point defects,the density and kind of defect associated with neutron irradiation fluence.It can be found the saturation magnetization first increases and then decreases with the irradiation fluence increases,meaning there is an optimum value for V_Znn concentration.When the neutron fluence is greater than 5×10⁹n/cm²,more unstable V_Znn combined with V_O to form zinc-oxygen divacancy(V_ZnO),indicating neutron irradiation changes the defect types.V_ZnOnO induces a smaller magnetic moment,thus the Ms decreased.To further verify the origin of RTFM,the CASTEP module was employed to calculate the magnetic and structural properties of native vacancy defects in ZnO.V_Znn induces 2.12?_B magnetic moment,only V_ZnOnO formed by the nearest V_Znn and V_O has 2.09?_B magnetic moment,while 3V_O cluster introduces a magnetic moment of¹?_B.Combined experiment and CASTEP calculation results,V_Znn is the most likely origin of RTFM.Using?-ray irradiated rutile TiO₂,the irradiation dose was 0 Gy,2×10³Gy,2×10⁴ Gy,4×10⁴ Gy,and 8×10⁴ Gy,respectively.The changes of sample structural,magnetic and optical properties before and after irradiation were analyzed.Since the displacement threshold energy of Ti atom is much bigger than that of O atom,the defects produced by?-ray irradiation are mainly oxygen vacancies.Therefore,the effect of V_O on ferromagnetism at room temperature can be studied separately.The main defects in the samples after radiation irradiation were V_O and Ti³⁺.The samples before and after irradiation showed RTFM and reached the maximum value when the radiation dose was 4×10⁴ Gy.Since the Ti³⁺ion is paramagnetic,room temperature ferromagnetism in the sample is mainly caused by V_O.Combined with the results of D-D neutron irradiation TiO₂,the contribution of V_O to RTFM in TiO₂ has been cleared by?-ray irradiation,and the concentration of V_O has an optimal value.