Investigation Of Ferromagnetism In Two-dimensional Transiton Metal Dichalcogenides

In recent years,with the fast development of spintronic devices and technologies,it is urgent to improve the density of data storage and lower the energy loss of the devices.Under the circumstance,the two-dimensional?2D?materials,which possess the smaller size and less energy loss compared with bulk materials,is becoming ideal candidates for future spintronic devices.Among them,the 2D transition metal dichalcogenides?TMDs?possessing excellent electronic and optical properties have attracted much attention of the researchers.However,most of them are intrinsic non-magnetic,which severely hindered their further applications in spintronics.Therefore,how to introduce room temperature ferromagnetism into 2D TMDs materials has become an issue of spintronics.Based on this,some works focusing on intrinsic ferromagnetism of TMDs have been reported recently,which endowed them the possibility of being used in spintronic devices.In this work,we introduced the ferromagnetism experimentally in typical 2D TMDs nanosheets?MoS₂ and MoSe₂?by defects-engineering,doping transition metal elements,and phase transferring.Besides,we found that the ferromagnetism could be adjusted by changing the parameters of experimental conditions such as nucleating temperature,ions irradiating doses,doping amount and phase ratios.The detailed works could be described as follows:1.The chemical vapor deposition?CVD?method was adopted to deposit MoSe₂nanosheets on SiO₂/Si and carbon clothes.By changing the nucleating temperature,the size and morphology of MoSe₂ could be adjusted.It is demonstrated that the robust ferromagnetism of MoSe₂ nanosheets?M_s=1.39 emu/g?is related to their surface defects and zig-zag edges,which was revealed both in the experiment and first-principle calculations.Through changing the nucleating temperature?from860?to 940??,the value of M_s ranged from 1.39 emu/g to the 0.015 emu/g.2.MoS₂ nanosheets were synthesized by hydrothermal method.Besides,some different types of transition metal elements,including magnetic elements?Fe,Co?and non-magnetic elements?Mn,Cr,Cu?,were doped in MoS₂.Each dopant was doped at different amounts.Through the magnetic measurements,it is demonstrated that when the doping amount is less than 10%,these dopants could introduce ferromagnetism in the MoS₂ nanosheets and obtained the maximum value of M_s?Fe:0.247 emu/g,Co:0.2 emu/g,Mn:0.015 emu/g,Cr:0.016 emu/g,Cu:0.023 emu/g?.What's more,with the doping amount increasing,the values of saturated magnetization?M_s?increased and then decreased in the experiment.3.Based on the solvothermal method,we synthesized MoX₂?X=S,Se?nanosheets and introduced 1T@2H structures in them.Besides,the ratios of 1T and2H structures could be controlled in the experiment.According to the previous first-principle calculation results and crystal-field theory,the Mo atoms of T phase could produce magnetic moments contributing ferromagnetism to the samples?maximum values of M_s:1.9 memu/g for MoS₂;8 memu/g for MoSe₂?.In addition,we synthesized the Re_xMo_1-xS₂ nanosheets,which also possess the 1T@2H structures.The magnetic measurement results indicated that the M_s of the samples varies with the ratios of 1T and 2H structures,which verifies that the ferromagnetism is closely correlated to the 2H and 1T phase structure matching,therefore,when the ratios of the two phases are compatible,the maximum value of M_s could be achieved?8 memu/g?.