Synthesis, Structure and Magnetic Properties of III-V Ferromagnetic Semiconductors

技术上的。智力优势：铁磁性III-V半导体的发展为展示磁性、磁光和半导体特性的新型多功能材料提供了可能性。这些材料提供了操纵自旋和电荷的潜力。然而，由于其较低的转变(居里)温度，它们的利用受到了阻碍。最近有报道表明，铁磁性半导体的居里温度超过300K。等电点表明，金属有机气相外延(MOVPE)制备的InMnAs合金的居里温度为330K。他最近的研究表明，居里温度的提高是由原子团簇引起的。问题是，稳定高温铁磁相的详细机制和磁性物种的性质是什么。在提出的方案中，将研究In基III-V铁磁半导体薄膜，包括InMnAs，InMnSb，InMnP及其固溶体。特别令人感兴趣的是过渡金属原子团簇在稳定这些半导体的高温铁磁性方面起到了什么作用，以及短程有序的性质是什么。还将考察自由载流子浓度对铁磁相稳定性的影响。根据最近的理论预测，是否可以在居里温度超过400K的情况下用MOVPE合成其他In基III-V化合物。本项目将采用金属有机气相外延技术制备外延合金薄膜。将制备不同带隙的半导体合金，以确定能带混合、杂质电离能和载流子局域化程度在稳定铁磁性中的作用。将使用的实验表征技术包括高分辨率电子显微镜、随温度和磁场变化的磁化强度测量、霍尔效应和磁阻。磁光克尔效应(MOKE)及其对红外-可见光区的光谱依赖性将被用来确定合金中交换作用的性质和大小。将使用扩展X射线精细结构分析(EXAFS)和具有原子尺度分辨率的局部电极原子探针来确定团簇的大小和分布。先进光子源的X射线吸收光谱和X射线磁性圆二色谱(XMCD)将用于确定组成合金的元素的磁性。阿贡的X射线光电子显微镜(PEEM)将与温度相关的磁力显微镜结合使用，以确定磁畴结构和稳定性。非技术性。更广泛的影响：该项目将涉及对研究生和本科生进行铁磁半导体合成和性能测量方面的培训。学生们还将参与阿贡的同步加速器研究。这些材料对新型自旋装置具有潜在的技术重要性，如自旋阀、磁性随机存取存储器和量子计算装置。

Technical. Intellectual merit: The development of ferromagnetic III-V semiconductors has provided the potential for a new class of multifunctional materials that exhibit magnetic, magneto-optical and semiconducting properties. These materials offer the potential for manipulating both spin and charge. Their utilization, however, has been impeded due to their low transition (Curie) temperatures. Recently there have been reports of ferromagnetic semiconductors with Curie temperatures in excess of 300 K. The PI has shown that InMnAs alloys prepared by metalorganic vapor phase epitaxy (MOVPE) exhibit a Curie temperature of 330 K. His recent research indicates that atomic clusters are responsible for the enhanced Curie temperature. The question arises as to the detailed mechanism for stabilizing the high temperature ferromagnetic phase and what is the nature of the magnetic species. In the proposed program In based III-V ferromagnetic semiconductor thin films will be studied including InMnAs, InMnSb, InMnP and their solid solutions. Of specific interest is what role do transition metal atomic clusters play in stabilizing high temperature ferromagnetism in these semiconductors and what is the nature of the short range order. The role of free carrier concentration on the ferromagnetic phase stability will also be examined. It is planned to determine whether or not other In based III-V compounds can be synthesized by MOVPE with Curie temperature in excess of 400 K as predicted by recent theory. In this project, epitaxial thin alloy films will be synthesized by metalorganic vapor phase epitaxy. Semiconductor alloys with different band gaps will be prepared to determine the role that band mixing, impurity ionization energy and degree of carrier localization play in stabilizing ferromagnetism. Experimental characterization techniques to be used include high resolution transmission electron microscopy, temperature and field dependent magnetization measurements, Hall effect and magnetoresistance. The magneto-optical Kerr effect (MOKE) and its spectral dependence over infra-red to visible region will be used to determine the nature and magnitude of the exchange interaction in the alloys. Extended x-ray fine structure analysis (EXAFS) and a local electrode atom probe with atomic scale resolution will be used to determine cluster size and distribution. X-ray absorption spectroscopy and x-ray magnetic circular dichroism (XMCD) at the Advanced Photon Source will be used to determine the magnetic properties of the elements comprising the alloys. X-ray photo-electron electron microscopy (PEEM) at Argonne will be used in conjunction with temperature dependent magnetic force microscopy to determine magnetic domain structure and stability. Non-Technical. Broader impact: The project will involve the training of graduate and undergraduate students in the synthesis and property measurements on ferromagnetic semiconductors. Students will also be involved in synchrotron studies at Argonne. These materials have potential technological importance for new types of spin devices such as spin valves, magnetic random access memories and quantum computation devices.