Experimental Studies On Magnetism Of Nonmagnetic Element Doped SnO₂ And SnS₂

Recently,the discovery of room-temperature ferromagnetism in pure and nonmagnetic element doped semiconductor materials challenges the traditional understanding of ferromagnetism and sparks a heated dispute on the ferromagnetic origin.This so-called d⁰ ferromagnetism effectively rules out the probable impact induced by the ferromagnetic secondary phases.The study on d⁰ ferromagnetic materials is very significant both for the fundamental science and practical applications.In this thesis,the nonmagnetic element doped SnO₂ and SnS₂ have been synthesized by sol-gel method and hydrothermal method,respectively.The structural,optical and magnetic properties of the doped samples were investigated systematically.Following works are mainly carried out:Sn_1-xLi_xO₂ nanoparticles were prepared by sol-gel method.XRD,XPS and absorption spectra analyses indicate that most Li atoms are incorporated into SnO₂ lattice and substitute for Sn atoms?LiSn?at low doping concentration?? 6 at.%?.With further doping?10 at.%?,additional Li atoms may go into interstitial sites?Lii?.The magnetic measurement indicates that all the samples show room-temperature ferromagnetism.The saturation magnetization increases non-monotonously with Li doping and the largest saturation magnetization of 2.44×10-3 emu/g appears in 6 at.% Li-doped SnO₂ sample.The analyses from structural,optical and magnetic measurements indicate that the origin of the ferromagnetism in Sn_1-xLi_xO₂ nanoparticles is attributed to the holes in O 2p orbital induced by LiSn.On the other hand,Lii acting as electron donors may combine with the holes induced by Li Sn and decrease the ferromagnetism.Sn_1-xSr_xO₂ nanoparticles were prepared by sol-gel method.Due to the different valence states of Sr²⁺ and Sn⁴⁺,XRD and XPS measurements indicate that Sr-doping introduces some oxygen vacancies in the samples.PL spectra analysis further reveals that most oxygen vacancies are in their V_O⁺ state,and the V_O⁺ concentrations increase with Sr concentration.Sr-doping can enhance the ferromagnetism in SnO₂ nanoparticles,and the variations of saturation magnetization and V_O⁺ concentrations follow a similar trend with increasing Sr concentration.This result suggests that the ferromagnetism of Sn_1-xSr_xO₂ nanoparticles have some connections with V_O⁺ defects.Sn_1-xMg_xS₂ nanoflowers were synthesized by hydrothermal method.The SEM measurement reveals that the samples exhibit flowerlike structures and each flowerlike structure consists of dozens of nanosheets.XRD and absorption spectra measurements indicate that Mg atoms are incorporated into SnS₂ matrix on two sites,substitutional site?MgSn?and interstitial site?Mgi?.MgSn can enhance the ferromagnetism and the alignment of magnetic moments is established through a p-p coupling interaction between the Mg 2p state and S 3p state.However,the enhanced ferromagnetism is destroyed by Mgi at higher Mg concentration due to the holes compensation effect.