【作者】 尤逢永；

【导师】 毕红；

【作者基本信息】 安徽大学 ， 无机化学， 2006， 硕士

【摘要】 近年来，因在稀释磁性半导体中表现出独特的磁有序现象而备受人们关注。主要是一方面因为它对所表现出的独特磁性的理解涉及到很多的基础性物理问题，另一方面这些独特的磁性蕴涵巨大的潜在应用前景。本文采用化学共沉淀法制备过渡金属Co²⁺离子掺杂的ZnO和ZnS基稀磁半导体（DMS）粉末。在合成的基础上，结合样品的结构分析和磁性行为，对样品磁性的起因进行了初步的探讨。具体内容如下： 概述了稀磁半导体的研究进展，重点介绍了ZnO基和ZnS基稀磁半导体的晶体结构、磁有关的效应以及稀磁半导体中磁性起因。迄今，文献上很多的研究集中在过渡磁性金属掺杂的稀磁半导体薄膜材料方面，对其粉末研究涉及很少。本文以探索一种重复性好的合成高居里温度的稀磁半导体粉体方法作为主要研究内容。 首先对获得具有室温铁磁性的Co掺杂ZnO的粉末样品的合成进行了探索。研究结果表明，溶液的陈化时间和共沉淀时的pH值是关键的控制因素，并以此提出了反应的机理。本文发现Zn_1-xCo_xO系列样品，在掺杂浓度较低时，室温下具有铁磁性，而掺杂浓度较高时，样品却表现出顺磁性。 本文在Co掺杂ZnO研究的基础上，进而对Co掺杂ZnS的粉末样品的合成进行了探讨，并对制备的样品进行了结构分析和磁性测试的实验研究。结果表明，Zn_1-xCo_xS样品也只有在低掺杂浓度情况下才能实现室温铁磁性。相对于Zn_1-xCo_xO粉末样品，在相同掺杂浓度和相同温度的情况下，Zn_1-xCo_xS的饱和磁化强度要大。 借助XRD分析研究了所制备的Co掺杂ZnO和Co掺杂ZnS两类样品的晶体结构。结果表明，合成出的Co掺杂ZnO具有纤锌矿型的晶体结构；Co掺杂ZnS样品具有闪锌矿和纤锌矿按1：1比例复合的混晶结构；在低掺杂浓度范围内，Co离子掺杂并没有引起ZnO和ZnS基体晶体结构的改变，且在仪器灵敏度范围内没有检测到第二相的存在。因此，我们认为观察到的铁磁性是稀磁半导体材料本征性质的体现，而不是源于第二相的出现或引入而引起的。 对稀磁半导体中的磁性起因有各种各样的解释，目前尚未达成共识。本文采用DMS中磁性离子间的近程超交换作用来解释所合成样品的磁行为，认为如果从稀磁半导体Zn_1-xCo_xO和Zn_1-xCo_xS的磁性起因来分析，增加巡游d电子的数量有利于铁磁耦合，因此需要很高的电子掺杂浓度，但是这种铁磁耦合是一种近程相互作用，必须在相邻Co²⁺离子的间距很短时才能起作用，因此需要增加Co²⁺离子的掺杂量使Co²⁺-Co²⁺之间的距离减小，但在一个合成过程中同时满足上述两个要求是很困难的，因此，铁磁样品的重复率普遍较低可能是由于以上两个条件相互竞争的结果。 迄今为止，文献上报道的研究内容相对集中在过渡磁性金属掺杂的稀磁半导体薄膜材料方面，得到的薄膜样品不仅居里温度低，而且呈现铁磁性的重复率不高。与之相比，我们摸索出加入络合剂的化学共沉淀法制备稀磁半导体粉末材料，并用此方法成功地获得具有室温铁磁性的Zn_1-xCo_xO和Zn_1-xCo_xS稀磁半导体粉末，采用该方法合成的样品不仅呈现铁磁样品的重复率比其它文献报道的要高得多，而且Zn_1-xCo_xS的居里温度远远高于文献报道的1.5～4.2K。更多还原

【Abstract】 Diluted magnetic semiconductors （DMSs）, which integrate the magnetism and semiconducting properties, are very significant from the view of both basic research and practical application. So far, research on diluted magnetic semiconductors is one of the hot topics in the world. In this thesis, transition metallic ions (Co²⁺) were introduced into ZnO and ZnS lattices by chemical co-precipitation method, the magnetic behaviors of Zn_1-xCo_xO （x = 0.01, 0.05, 0.12, 0.15, 0.42） and Zn_1-xCo_xS （x = 0.013, 0.021, 0.065, 0.068） samples and their ferromagnetism origins were also studied. The main content of the thesis is as follows:The research background and application perspectives of DMSs are introduced in Chapter 1. Some of basic properties of DMSs such as lattice structure, magnetic effect, origin of ferromagnetism are also reviewed. To our knowledge, few reports deal with magnetic properties of Co-doped DMS powder samples. Therefore, our study focus on the synthesis and magnetism of the Co-doped ZnO and Co-doped ZnS power samples.The synthesis process of the Zn_1-xCo_xO samples had been studied firstly. It shows that the aging time of the solution and pH value of the coprecipitation are two key factors to synthesize Zn_1-xCo_xO samples. Then a possible mechanism of the reaction is proposed based on coordination chemistry. The results indicate that ferromagnetic behavior at room temperature of Zn_1-xCo_xO samples only presents in low doping content samples, and unexpectedly, those doped samples in high doping content only show paramagnetism at room temperature.The similar phenomenon has been observed in the synthesized Zn_1-xCo_xS samples — only the samples in low doping content show ferromagnetic behavior at room temperature. Moreover, the magnetization of Zn_1-xCo_xS sample is much larger than that of Zn_1-xCo_xO samples with the same doping content.The XRD results indicate that all Zn_1-xCo_xO samples own Wurtzite crystalline structure in low doping content, and all Zn_1-xCo_xS samples are mixture of cubic and hexagonal crystalline. Moreover, those samples with low doping content showferromagnetic behavior at room temperature and no secondary magnetic phase has been found in our measurements. It is suggested that the ferromagnetism of the samples is the intrinsic property of the Co-doped DMSs but not comes from the secondary phase. However, since there are a lot of reports on synthesis and magnetic properties of Co-doped diluted magnetic semiconductors, these results are very different and even more some of them are contradictory, there exist various arguments on origin of the ferromagnetism of Co-doped DMSs. In our paper, a possible origin of the magnetization behaviors of the Zn_1-xCo_xO and Zn_1-xCo_xS samples has been proposed based on super-exchange coupling mechanism between neighboring magnetic metal ions. It can give a reasonable explanation for all of our experimental results.Up to date, most of the reported DMSs films show not only very low Curie temperatures but also much poor reproducibility. On the contrary, our Zn_1-xCo_xO and Zn_1-xCo_xS samples synthesized by the chemical coprecipitation method present room-temperature ferromagnetism as well as good reproducibility, which means their potential wider applications in the future.更多还原