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Microstructure And Magnetic Behavior Of Oxides Doping With Cobalt

Posted on:2013-12-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:H JiangFull Text:PDF
GTID:1221330392458325Subject:Materials Science and Engineering
Abstract/Summary:PDF Full Text Request
Magnetic semicondutors possess the properties of magnetic materials andsemiconductors, which become the important materials of potential new generation ofspintronic devices. Magnetic semiconductors are achieved by doping magnetic elementsinto semiconductors. The magnetic properties and exchange bias effect of transitionmetal doped oxide semiconductor inspired tremendous investigations. However, theexperimental and theoretical problems have not been fully understood and restrict itsdevelopment. In this dissertation, Co-doped SnO2and CuO nanorods are synthesized bychemical solution methods; CuO films are prepared by magnetron sputtering and strongmagnetic annealing. Through changing experimental conditions (dopants concentration,surfactants addition, annealing), we systematically investigate the morphology,structural defects, dopants distribution, microstructure and dopants local structure.Based on the above studies, the research discuss the correlations between microstructure,surface character and magnetic behavior. The ferromagnetic mechanism as well as theexchange bias mechanism are further explained.All the Co doped SnO2nanorods synthesized by solvethermal methods have singletetragonal rutile SnO2phase. The secondary phases was not found. The results confirmthe intrinsic nature of ferromagnetism. The introduction of surfactant suppresses theformation of Co clusters and promote the defects forming. The rolling process has beenproposed for the possible formation mechanism, and reasonabley explains the mediationeffect of surfactants on the structural defects. The room-temperature ferromagnetismtuned by and structural defects and surfaces. Different amounts of surfactant andannealing have been used in order to surface modificating the nanoparticls. Theexperimental results demonstrate surface defects is the key factor in mediatingferromagnetism. Aggregation and dispersion model is used to explain the effect ofsurface modification on ferromagnetism in details. Atmosphere annealing confims thecrucial roles of oxygen vacancies in tuning magnetic properties. Finally, we reasonableyexplained the origin of room-temperature ferromagnetism.Antiferromagnetic oxides were introduced in magnetic semiconductors. We havesynthesized Co doped CuO nanorods, and also found room-temperature ferromagnetism in trastion metal doped antiferromgnetic oxides. The results expand the extent ofmagnetic semiconductors. Based on the development of doped antiferromagntic oxides,we frabricated the CuO films by two stpes including sputtering and annealing,meanwhile the strong magnetic field is applied in the growth process of CuO films. Thestrong magnetic field promote the grain refinement and improve the crystallinity of thefilms, but not influence the state of oxidation. With the increase of field intensity, theferromagnetism dramatically declines and finally disappares. However, the effect ofexchange bias enhances continously. The above phenomenon is attributed to orientationeffect and the suppression of diffusion by strong magnetic field. This study opens a newway to tune the magnetic behavior in nanomaterials.
Keywords/Search Tags:magnetic oxide, microstructure, room-temperature ferromagnetism, exchange bias, strong magnetic field
PDF Full Text Request
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