金红石相TiO_2单晶缺陷类型和室温铁磁性起源的研究
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摘要
同时具有磁性和半导体性的稀磁半导体材料,由于其在自旋电子学器件中的潜在应用,所以引起了人们的极大关注。虽然通过掺杂已经在很多的氧化物中发现了室温铁磁性,但是对于室温铁磁性的起源仍存在较大的争议。通过调研发现,研究具有d0磁性的氧化物可以很好的解决室温铁磁性的起源问题。
本文主要以金红石Ti02单晶作为研究样品,通过高温高真空热处理和N离子掺杂的方法处理样品,然后利用X射线衍射谱(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、正电子湮没寿命谱(PALS).X射线近边吸收结构(XANES).慢正电子束流和超导量子干涉仪(SQUID)等测试手段,针对处理样品的缺陷类型和室温铁磁性的起源问题进行了表征,并对测试结果做了进一步分析和处理。
根据测试结果可知,高温高真空热处理的样品中主要的缺陷是O空位(V。)和Ti3+-Vo复合缺陷,且这两种缺陷都属于本征缺陷；热处理样品的室温铁磁性与O空位紧密相连,Ti3+离子中不成对电子的自旋磁矩是产生室温铁磁性的根本来源；另外,当金红石Ti02晶格中存在大量的过剩O离子时,它们又可以诱导Ti空位(VTi)的产生,Ti空位的出现可以导致样品饱和磁化强度的显著增大。N离子注入样品的缺陷类型主要包括O空位、Ti空位和VTi-No复合缺陷；辐照样品室温铁磁性的起源可以归功于Ti空位和N原子替代O原子(No),N原子替代0原子能够诱使铁磁性有序化的开始,而Ti空位的产生则能增强室温铁磁性的饱和磁化强度。
Dilute magnetic semiconductors (DMSs) have attracted much interest due to their favorable magnetic and semiconducting properties for application of spin-dependent electronic devices. Although many diluted magnetic oxides have been found room temperature ferromagnetism (RTFM) by doping, there is still great debate on the origin of room temperature ferromagnetism. By researching Literature, it is found that d0magnetic oxides can be very good to solve the origin of room temperature ferromagnetism.
This paper applies rutile TiO2single crystals as the research sample. The samples are dealing with heat treatment of high temperature and high vacuum and N ions doping. Then by using X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), positron annihilation lifetime spectroscopy (PALS), X-ray absorption near edge structure (XANES), slow positron beam and superconducting quantum interference device (SQUID), defect types and room temperature ferromagnetism were characterized. The test results were further analyzed and processed.
According to the test results, a lot of oxygen vacancies (Vo) and especially Ti3+-Vo defect complexes are formed in high vacuum annealing samples. And two kinds of defects are the intrinsic defects. It can be demonstrated that room temperature ferromagnetism of annealed samples in high vacuum is closely associated with oxygen vacancies. The unpaired3d electrons in Ti3+ions provide vast spin magnetic moments which are decisively related to the observed ferromagnetism. In addition, when there is excess oxygen ions in rutile TiO2lattice, they also can produce Ti vacancies (VTi) which increase magnetization obviously. Many oxygen vacancies, titanium vacancies and VTi-No complexes are generated due to N ion irradiation. The room temperature ferromagnetism is attributed to oxygen vacancies and substitution of0with N (No) defects in the rutile structure. The production of titanium vacancies can enhance the RTFM, and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.
本文主要以金红石Ti02单晶作为研究样品,通过高温高真空热处理和N离子掺杂的方法处理样品,然后利用X射线衍射谱(XRD)、扫描电子显微镜(SEM)、X射线光电子能谱(XPS)、正电子湮没寿命谱(PALS).X射线近边吸收结构(XANES).慢正电子束流和超导量子干涉仪(SQUID)等测试手段,针对处理样品的缺陷类型和室温铁磁性的起源问题进行了表征,并对测试结果做了进一步分析和处理。
根据测试结果可知,高温高真空热处理的样品中主要的缺陷是O空位(V。)和Ti3+-Vo复合缺陷,且这两种缺陷都属于本征缺陷；热处理样品的室温铁磁性与O空位紧密相连,Ti3+离子中不成对电子的自旋磁矩是产生室温铁磁性的根本来源；另外,当金红石Ti02晶格中存在大量的过剩O离子时,它们又可以诱导Ti空位(VTi)的产生,Ti空位的出现可以导致样品饱和磁化强度的显著增大。N离子注入样品的缺陷类型主要包括O空位、Ti空位和VTi-No复合缺陷；辐照样品室温铁磁性的起源可以归功于Ti空位和N原子替代O原子(No),N原子替代0原子能够诱使铁磁性有序化的开始,而Ti空位的产生则能增强室温铁磁性的饱和磁化强度。
Dilute magnetic semiconductors (DMSs) have attracted much interest due to their favorable magnetic and semiconducting properties for application of spin-dependent electronic devices. Although many diluted magnetic oxides have been found room temperature ferromagnetism (RTFM) by doping, there is still great debate on the origin of room temperature ferromagnetism. By researching Literature, it is found that d0magnetic oxides can be very good to solve the origin of room temperature ferromagnetism.
This paper applies rutile TiO2single crystals as the research sample. The samples are dealing with heat treatment of high temperature and high vacuum and N ions doping. Then by using X-ray diffraction (XRD), scanning electron microscope (SEM), X-ray photoelectron spectroscopy (XPS), positron annihilation lifetime spectroscopy (PALS), X-ray absorption near edge structure (XANES), slow positron beam and superconducting quantum interference device (SQUID), defect types and room temperature ferromagnetism were characterized. The test results were further analyzed and processed.
According to the test results, a lot of oxygen vacancies (Vo) and especially Ti3+-Vo defect complexes are formed in high vacuum annealing samples. And two kinds of defects are the intrinsic defects. It can be demonstrated that room temperature ferromagnetism of annealed samples in high vacuum is closely associated with oxygen vacancies. The unpaired3d electrons in Ti3+ions provide vast spin magnetic moments which are decisively related to the observed ferromagnetism. In addition, when there is excess oxygen ions in rutile TiO2lattice, they also can produce Ti vacancies (VTi) which increase magnetization obviously. Many oxygen vacancies, titanium vacancies and VTi-No complexes are generated due to N ion irradiation. The room temperature ferromagnetism is attributed to oxygen vacancies and substitution of0with N (No) defects in the rutile structure. The production of titanium vacancies can enhance the RTFM, and substitution of O with N is the onset of ferromagnetism by inducing relatively strong ferromagnetic ordering.
引文
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[2]王学忠,陈辰嘉,王荣明等Cd1-xMnxTe的巨大法拉第旋转与激子跃迁[J].半导体学报,1994,15(5)：333
[3]刘宣华,张连生.稀释磁性半导体[J].物理学进展,1994,14(1)：3
[4]Anderson P W.Magnetism ed G Rado and H Suhl[M].New York:Academic,1963
[5]White R. Quantum Theory of Magnetism[M].Berlin:Springer,1983
[6]Dietl T, Ohno H, Matsukura F, et al.Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors[J].Science,2000,287:1019
[7]Pearton S J, Heo W H, Will M, et al.Dilute magnetic semiconducting Semiconductor Science oxides[J]. and Technology,2004,19:R59
[8]Matsumoto Y, Murakami M, Shono T, et al.Room-Temperature Ferromagnetism in Transparent Transition Metal-Doped Titanium Dioxide[J].Science,2001,291:854
[9]Chambers S A, Heald S M, Droubay T.Local Co structure in epitaxial CoxTi1-xO2-x anatase[J].Physical Review B,2003,67:100401
[10]Grifin K A, Varela M, Pennycook S J, et al.Atomic-scale studies of cobalt distribution in Co-TiO2 anatase thin films:Processing, microstructure, and the origin of ferromagnetism[J]. Journal of Applied Physics,2006,99(8):08M114
[11]Bryan J D, Santangelo S A, Keveren S C, et al.Activation of High-Tc Ferromagnetism in Co2+:TiO2 and Cr3-:Ti02 Nanorods and Nanocrystals by Grain Boundary Defects[J].Journal of the American Chemical Society,2005,127(44):15568
[12]Manivannan A, Seehra M S, Majumder S B, et al.Magnetism of Co-doped titania thin films prepared by spray pyrolysis[J].Applied Physics Letters,2003,83(1):111
[13]Errico L A, Weissmann M, Renteria M.Ab initio study of ferromagnetism induced by magnetic impurities in rutile TiO2[J].Physica Status Solidi (b),2004, (10):2399
[14]Cruz M M, da Silva R C, Franco N, et al.Ferromagnetism induced in rutile single crystals by argon and nitrogen implantation[J].Journal of Physics:Condensed Matter,2009,21:206002
[15]Venketesan M, Fitzgerald C B, Coey J M D.Thin films:Unexpected magnetism in a dielectric oxide[J].Nature,2005,430:630
[16]Hong N H, Sakai J, Poirot N, et al.Room-temperature ferromagnetism observed in undoped semiconducting and insulating oxide thin films[J].Physical Review B,2006.73(13):132404
[17]Yoon S D, Chen Y, Yang A, et al.Oxygen-defect-induced magnetism to 880 K in semiconducting anatase TiO2-δ films[J].Journal of Physics:Condensed Matter,2006,18: L355
[18]Griffin R K, Varela M, Rashkeev S, et al.Defect-mediated ferromagnetism in insulating Co-doped anatase TiO2 thin films[J].Physical Review B,2008,78(1):014409
[19]Yan W S, Sun Z H, Pan Z Y, et al.Oxygen vacancy effect on room-temperature ferromagnetism of rutile Co:Ti02 thin films[J].Applied Physics Letters,2009,94(4):042508
[20]Dietl T, Ohno H, Matsukura F, et al.Zener Model Description of Ferromagnetism in Zinc-Blende Magnetic Semiconductors[J].Science,2000,287:1019
[21]Patel S K S, Gajbhiyea N S, Date S K.Ferromagnetism of Mn-doped TiO2 nanorods synthesized by hydrothermal method[J]. Journal of Alloys and Compounds,2011,509S:S427
[22]郁伟中.正电子物理及其应用[M].科学出版社,2003
[23]Tao S J.Methods of Data Reduction in Analyzing Positron Annihilation Lifetime Spectra[J]. IEEE.Trans.Nucl.sci.,1986,15(1)::175
[24]王淑英.多指数曲线拟合分解正电子湮灭寿命谱的方法[J].核技术,1982,5(6)：81
[25]腾敏康,夏元复.正电子湮没谱学及其应用[M].北京：原子能出版社,2000
[26]Triftshauser W. Positron Annihilation[J].Topics in Current Physics, Micropic Methods in Metals,1986,40:49
[27]Campbell J L.ANNIHILATION GAMMA-RAY LINESHAPE PARAMETERS[J].Applied Phyics,1977,13 (4):365
[28]Connors D C, Crisp V H C, West R N.The effects of vacancies on positron annihilation in cadmium[J]. Journal of Physics F:Metal Physics,1971,355
[29]Asoka-Kumar P, Alatalo M, Ghosh V J, et al.Increased Elemental Specificity of Positron Annihilation Spectra[J].PHYSICAL REVIEW LETTERS,1996,77 (10)
[30]Mills A P.POSITRONIUM FORMATION AT SURFACES[J].Phys.Rev.Lett.,1978,41:1828
[31]Mills A P.EFFICIENT GENERATION OF LOW-ENERGY POSITRONS[J].Appl.Phys. Lett.,1979,35:427
[32]Begemann M.Slow positron beam production by a 14 MeV C.W. electron accelerator[J]. Nucl.Instr.Meth.,1982,201:287
[33]Dietl T, Ohno H, Matsukura F, et al.Zener model description of ferromagnetism in zinc-blende magnetic semiconductors[J]. Science,2000,287 (5455):1019
[34]Pearton S J, Heo W H, Ivill M, et al.Dilute magnetic semiconducting oxides[J]. Semiconductor Science and Technology,2004,19:R59
[35]Li T J, LI G P, Gao X X, et al.Observation of Room Ferromagnetism in Cu-Implanted Crystal ZnO[J]. Chin. Phys. Lett.,2000,27:087501
[36]Ouyang Q Z, Ye Z Q, Lei M S, et al. First principles study on the structural,electronic and optical properties of diluted magnetic semiconductors Zn1-xCoxX (X=S, Se, Te) [J].Chin. Phys.B,2006,15:1585
[37]Zhao Y H, Cheng L Z, He K Y, et al.The effect of Nb addition on the thermal stability and magnetic properties of Fe-based amorphous alloys with a wide supercooled liquid region[J]. Chin. Phys. B,2002,11:77
[38]Matsumoto Y, Murakami M, Shono T, et al. Room-Temperature Ferromagnetism in Transparent Transition Metal-Doped Titanium Dioxide[J]. Science,2001,291:854
[39]Xu X G, Jiang Y, Yu G H, et al. Distribution and magnetization of Co near the rutile TiO2 (110) surface:A first-principles study[J].Phys. Lett. A,2008,372:2098
[40]Janisch R, Spaldin N A.Understanding ferromagnetism in Co-doped TiO2 anatase from first principles[J].Phys.Rev.B,2006,73:035201
[41]Mallia G, Harrison N M.Magnetic moment and coupling mechanism of iron-doped rutile TiO2 from first principles[J].Phys. Rev. B,2007,75:165201
[42]Du X S, Li Q X, SuHB, et al. Electronic and magnetic properties of V-doped anatase TiO2 from first principles[J].Phys. Rev. B,2006,74:233201
[43]Pammaraju C D, Sanvito S.Ferromagnetism Driven by Intrinsic Point Defects in HfO2[J]. Phys. Rev. Lett.,2005,94:217205
[44]Lu J B, Yang K S, Jin H, et al.First-principles study of the electronic and magnetic properties of oxygen-deficient rutile TiO2(110) surface[J]. J. Solid State Chem.,2011,184:1148
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