K掺杂SnO_2和V掺杂ZnO稀磁半导体粉末的结构和磁性研究
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摘要
稀磁半导体( DMSs )是指在非磁性半导体材料基体(通常是AB )中通过掺入少量磁性过渡族金属元素或稀土金属元素使其获得铁磁性能的一类新型功能材料。目前,在DMSs材料中发现了许多新的物理现象,如巨法拉第效应、巨塞曼分裂、反常霍尔效应、巨负磁阻效应、磁致绝缘体金属转变等。利用这些效应,可以制备出各种新型功能器件,为一些科技的发展提供条件。因此,这种新型材料的研究倍受人们的关注。
本文利用溶胶-凝胶法成功地制备出了一系列K-SnO_2和V-ZnO稀磁半导体纳米粉末。利用X射线衍射仪( XRD )、透射电镜( TEM )、X射线光电子能谱( XPS )及物理性能测试仪( PPMS-9 )中的样品振动磁强计( VSM )对样品的结构和磁性进行了表征。
在K-SnO_2体系中,所有样品均为二氧化锡金红石结构,颗粒大小约几个纳米;K元素以+1价存在;样品具有室温铁磁性,且饱和磁化强度随着掺杂浓度的增大而增强。将K掺杂浓度为4%的样品和纯SnO_2样品在氧气下退火后,掺杂K的样品仍然具有室温铁磁性,因此氧空位不是引起铁磁性的主要来源。当一个K元素取代一个Sn的位置时,由于K、Sn化合价的不同,将会产生3个阴离子空穴,阳离子可以通过这些空穴发生间接交换作用,从而导致铁磁性,具体磁学机理可以用RKKY模型来解释。
在V-ZnO体系中,V掺杂浓度低于5%时,样品具有氧化锌纤锌矿多晶结构,颗粒尺寸在二三十个纳米左右;V元素的化合价为+5价;样品呈现室温铁磁性,且样品的饱和磁化强度随着V掺杂浓度的增大而增强,掺杂浓度为3%的样品在不同温度( 500℃,600℃,700℃)的空气下退火1h后,饱和磁化强度随着退火温度的升高而增强。我们认为样品中的铁磁性来源主要是由氧空位和缺陷态密度引起的,具体磁学机理可以用束缚磁极化子模型来解释。
Diluted magnetic semiconductors ( DMSs ) is a new type of functional materials, which can be obtained by using a small amount of magnetic transition metal elements or rare earth elements to replace the cations in the non-magnetic semiconductor materials ( usually AB type ). Currently, people have discovered many new physical phenomena in the DMSs materials, such as giant Faraday effect, giant Zeeman splitting, anomalous Hall effect, giant negative magnetoresistance, magnetic mnsulator-metal transition and so on. Some new functional devices can be prepared when using these effects and will provide a new way to technology development. So now it is attracting people’s more and more attention.
In this thesis, a series of K-SnO_2 and V-ZnO diluted magnetic semiconductor nanoparticles had been synthesized by sol-gel method. Structural and magnetic measurements were carried out by X-ray diffraction( XRD ), Transmission electron microscopy( TEM ), X-ray photoelectron spectroscopy( XPS ), and Vibrating sample magnetometer( VSM ), respectively.
In the K-SnO_2 DMSs, We found that all nanopowders peaks can be identified with those of pure rutile SnO_2 nanopowders. The size of the nanoparticles is about a few nanometers. K ions have a valence of +1. Magnetization measurements revealed that the samples with K doping exhibited room temperature ferromagnetism, and the saturation magnetization was enhanced as the concentration of K-doped increased. Ferromagnetism still existed in Sn_(0.96)K_(0.04)O_2 when annealed in O_2 at 400℃for 1h, so we can conclude that oxygen vacancies are not the main origin of the ferromagnetism. When a K ion replaces a Sn ion, three anion holes will appear because of the difference between the valence of K ions and Sn ions. Exchange interactions will be occurred between cations and holes and finally lead to ferromagnetism. The specific mechanism of magnetic can be explained by RKKY model.
In the V-ZnO DMSs, we found that the samples peaks with the V ions concentration less than 5% can be identified with typical wurtzite structure of ZnO, and the size of the nanoparticles is about a few nanometers. V ions have a valence of +5. According to magnetic measurement, all the samples with V doping exhibited room temperature ferromagnetism, and the saturation magnetization of the sample was enhanced as the concentration of V-doped increased. When Zn_(0.97)V_(0.03)O was annealed at different temperatures (500℃, 600℃, 700℃) in the air for 1h, the saturation magnetization was also enhanced with the increasing temperatures. We can conclude that oxygen vacancies and the concentration of defects are the main origin of the ferromagnetic in V-ZnO DMSs, and the specific mechanism of magnetic can be explained by BMPs model.
本文利用溶胶-凝胶法成功地制备出了一系列K-SnO_2和V-ZnO稀磁半导体纳米粉末。利用X射线衍射仪( XRD )、透射电镜( TEM )、X射线光电子能谱( XPS )及物理性能测试仪( PPMS-9 )中的样品振动磁强计( VSM )对样品的结构和磁性进行了表征。
在K-SnO_2体系中,所有样品均为二氧化锡金红石结构,颗粒大小约几个纳米;K元素以+1价存在;样品具有室温铁磁性,且饱和磁化强度随着掺杂浓度的增大而增强。将K掺杂浓度为4%的样品和纯SnO_2样品在氧气下退火后,掺杂K的样品仍然具有室温铁磁性,因此氧空位不是引起铁磁性的主要来源。当一个K元素取代一个Sn的位置时,由于K、Sn化合价的不同,将会产生3个阴离子空穴,阳离子可以通过这些空穴发生间接交换作用,从而导致铁磁性,具体磁学机理可以用RKKY模型来解释。
在V-ZnO体系中,V掺杂浓度低于5%时,样品具有氧化锌纤锌矿多晶结构,颗粒尺寸在二三十个纳米左右;V元素的化合价为+5价;样品呈现室温铁磁性,且样品的饱和磁化强度随着V掺杂浓度的增大而增强,掺杂浓度为3%的样品在不同温度( 500℃,600℃,700℃)的空气下退火1h后,饱和磁化强度随着退火温度的升高而增强。我们认为样品中的铁磁性来源主要是由氧空位和缺陷态密度引起的,具体磁学机理可以用束缚磁极化子模型来解释。
Diluted magnetic semiconductors ( DMSs ) is a new type of functional materials, which can be obtained by using a small amount of magnetic transition metal elements or rare earth elements to replace the cations in the non-magnetic semiconductor materials ( usually AB type ). Currently, people have discovered many new physical phenomena in the DMSs materials, such as giant Faraday effect, giant Zeeman splitting, anomalous Hall effect, giant negative magnetoresistance, magnetic mnsulator-metal transition and so on. Some new functional devices can be prepared when using these effects and will provide a new way to technology development. So now it is attracting people’s more and more attention.
In this thesis, a series of K-SnO_2 and V-ZnO diluted magnetic semiconductor nanoparticles had been synthesized by sol-gel method. Structural and magnetic measurements were carried out by X-ray diffraction( XRD ), Transmission electron microscopy( TEM ), X-ray photoelectron spectroscopy( XPS ), and Vibrating sample magnetometer( VSM ), respectively.
In the K-SnO_2 DMSs, We found that all nanopowders peaks can be identified with those of pure rutile SnO_2 nanopowders. The size of the nanoparticles is about a few nanometers. K ions have a valence of +1. Magnetization measurements revealed that the samples with K doping exhibited room temperature ferromagnetism, and the saturation magnetization was enhanced as the concentration of K-doped increased. Ferromagnetism still existed in Sn_(0.96)K_(0.04)O_2 when annealed in O_2 at 400℃for 1h, so we can conclude that oxygen vacancies are not the main origin of the ferromagnetism. When a K ion replaces a Sn ion, three anion holes will appear because of the difference between the valence of K ions and Sn ions. Exchange interactions will be occurred between cations and holes and finally lead to ferromagnetism. The specific mechanism of magnetic can be explained by RKKY model.
In the V-ZnO DMSs, we found that the samples peaks with the V ions concentration less than 5% can be identified with typical wurtzite structure of ZnO, and the size of the nanoparticles is about a few nanometers. V ions have a valence of +5. According to magnetic measurement, all the samples with V doping exhibited room temperature ferromagnetism, and the saturation magnetization of the sample was enhanced as the concentration of V-doped increased. When Zn_(0.97)V_(0.03)O was annealed at different temperatures (500℃, 600℃, 700℃) in the air for 1h, the saturation magnetization was also enhanced with the increasing temperatures. We can conclude that oxygen vacancies and the concentration of defects are the main origin of the ferromagnetic in V-ZnO DMSs, and the specific mechanism of magnetic can be explained by BMPs model.
引文
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[2]闰发旺,梁春广,半导体情报,2001,38(6):2-7
[3] H. Ohno, Making nonmagnetic semiconductors ferromagnetic, Science, 1998, 281: 951-955
[4] Nagaev E L, Physics of Magnetic Semiconductors [M], MIR Moscow, 1983
[5] Craik D J, Magnetic Oxides[M]. wiley New York, 1975
[6] Ohno H, Making Nonmagnetic Semiconductors Ferromagnetic[J], Science, 1998, 281: 951
[7] H. Munekata, H. Ohno, S. von Molnar, Armin Segmüller, L. L. Chang, and L. Esaki, Diluted magnetic III-V semiconductors, Phys. Rev. Lett. 1989, 63: 1849-1852
[8] Munekata H, Ohno H, von Molnar S, et al, Diluted magnetic III-V semiconductors[J], Phys Rev Lett, 1989, 63(17): 1849-1852
[9] Ohno H, Shen A, Matsukura F, et al, (Ga,Mn)As: A new diluted magnetic semiconductor based on GaAs[J], Appl Phys Lett, 1996, 69(3): 363-365
[10] T. Dielt, H. Ohno, F. Matsukura, et al, Zener Model Description of ferromagnetism in Zinc-Blende magnetic semiconductors, Science, 2000, 287: 1019-1022
[11] D. Iusan, B. Sanyal, O. Eriksson, et al, Influence of defects on the magnetism of Mn-doped ZnO, J. Appl. Phys, 2007, 101: 09H101
[12] Zhi-Ren Wei, Zhi-Qiang Li, Guo-Yi Dong, Origin of high-temperature ferromagnetism in Zn_(0.98)Fe_(0.02)O alloys prepared by hydrothermal method, J. Magn. Magn. Mater, 2008, 320: 916-918
[13] Michael Snure, Dhananjay Kumar, Ashutosh Tiwari, Ferromagnetism in Ni-doped ZnO films: Extrinsic or intrinsic? Appl Phys Lett, 2009, 94: 012510
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