Investigation On Structure And Room Temperature Magnetic Properties Of Mn Or Co Doped ZnO

Diluted magnetic semiconductors(DMSs)are novel materials by doping transition metal ions into semiconductor compounds.And,ZnO dilute magnetic semiconductor(DMS)is the most promising to be integrated into the traditional semiconductors.It can not only make the processing size of traditional microelectronic devices smaller,but also improve the transmission efficiency greatly.In recent years,the research of ZnO DMS has been a hot topic in this field gradually.However,ZnO DMS which only possessed the room temperature ferromagnetism can be used in practical application.Therefore,the sol-gel method to prepare Mn or Co doped ZnO DMS was chosen in this paper and optimized a part of processing parameters.Meanwhile,all the samples were analysed by XRD,SEM,EDAX,FTIR,UV-vis,XPS,VSM and PPMS detection techniques.The crystal structure and the room temperature magnetism origin of ZnO DMS were explored deeply.The results were obtained as following.(1)0%,3%,6%and 9%Mn doped ZnO samples were prepared by sol-gel method.The XRD results showed that the second phase impurity(Zn Mn O₃ compound)was formed as increasing of doping Mn content,but it was little effect on the room temperature magnetism properties of Mn doped ZnO system.At the same time,SEM,EDAX,FTIR and XPS showed that Mn ions were successfully doped into the crystal structure of ZnO and replaced the position of Zn ions in divalent state.In addition,VSM analysis results suggested that all of samples were composed by two magnetism that room temperature diamagnetism and paramagnetism.And,the room temperature magnetism properties of all samples were observed by the magnetism competition mechanism.Namely,the Mn doped ZnO samples exhibited diamagnetism mainly in the low external magnetic field,which provided by the dia-magnetic phase and the anti-ferromagnetism exchange interaction among Mn ions.However,in the larger external magnetic field,the magnetism properties of Mn doped ZnO samples displayed paramagnetism,which provided by the hybridization among Mn,Zn and O ions.(2)0%,1%,2%and 3%Mn doped ZnO samples were prepared by sol-gel method.XRD results showed that there was no second phase impurity in the crystal structure of all samples.SEM results showed the particle size of the samples decreased with increasing of doping Mn content.XPS results showed Mn ions were successfully doped into the crystal structure of ZnO and replaced the position of Zn ions in divalent state.In addition,VSM analysis results showed that all of samples were composed by room temperature ferromagnetism and diamagnetism.And,the room temperature magnetism properties exhibited were determined by the ratio of ferro-magnetic phase to diamagnetism.In other words,the room temperature ferromagnetism of 1%Mn doped ZnO sample was provided by the higher ferro-magnetic phase mainly.The room-temperature ferromagnetism of 2%,3%Mn doped ZnO samples were provided by the hybridization between Zn,Mn and O ions.Meanwhile,the hybridization between oxygen vacancies and magnetic ions provided the room temperature ferromagnetism.The room temperature diamagnetism of all doped samples was provided by the dia-magnetic phase.(3)0%,1%,3%and 5%Co doped ZnO samples were prepared by sol-gel method.XRD results showed that there was no any secondary phase impurity in the crystal structure of all samples.SEM results showed the particle size of the sample decreased with increasing of doping Co content.Based on the results of FTIR,UV-Vis and XPS tests,the position of Zn²⁺ions in ZnO hexagonal wurtzite were replaced by Co ions and the doped Co ions were dominantly in divalent state.PPMS results suggested that the doped ZnO samples possessed the room temperature dia-magnetic behavior.All of Co doped ZnO samples possessed the room temperature ferro-magnetic behavior,which provided by the hybridization among Mn,Zn and O ions.And,it was also provided by the d-d exchange among Co ions.(4)Compared room temperature magnetism properties of Mn or Co doped ZnO system,the magnetism moment direction of the magnetism cations was conducive to display the ferromagnetism order state when the doped content was less than 5%.Hence,all of doping samples exhibited room temperature ferromagnetism.At the same time,lower doping content can avoid the formation of the second phase impurity compounds effectively and reduce oxygen vacancy concentration.