Disorder Effects on Magnetism in Dilute Magnetic Semiconductors

稀磁半导体中磁性的无序效应

• 批准号: 1305666
• 负责人: Bruce Wessels
• 金额: $ 27.29万
• 依托单位: Northwestern University
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2013
• 资助国家: 美国
• 起止时间: 2013-09-01 至 2015-08-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=1305666&HistoricalAwards=false
• 关键词: Disorder; Effects; Magnetism; Dilute; Magnetic

Technical Description: Group III-V compound dilute magnetic semiconductors (DMS) offer the potential for manipulating both spin and charge and a class of materials that exhibit magnetic, magneto-optical and semiconducting properties. Their utilization, however, has been impeded due to their low magnetic transition (Curie) temperatures. It was demonstrated that InMnSb alloys prepared by metalorganic vapor phase epitaxy exhibit a Curie temperature in excess of 400 K. Mn dopant atoms were imaged using cross-sectional scanning tunneling microscopy (STM). No clustering of Mn was noted but positional disorder was observed. The inhomogeneous distribution of magnetic ions on the atomic scale is proposed to play a dominant role in the magnetic behavior.The objective of this research project centers on determining the magnetic phase diagram of DMS in the dilute concentration limit. The alloy system of interest is the narrow-gap DMS InMnSb. The applicability of a theoretical model for describing the magnetic properties of disordered DMS is investigated. The major questions to be answered are (a) why these alloys have high Curie temperatures and (b) what the role of disorder of Mn dopants is on the transition temperature. In the project, epitaxial thin alloy films are deposited by metalorganic vapor phase epitaxy. Alloys with Mn concentrations of less than 1% and carrier concentrations of lower than 10^19 cm-3 are synthesized. The role of disorder in stabilizing the ferromagnetic phase is investigated. It is proposed that the ferromagnetic phase is stabilized at carrier concentrations 2 x 10^17 cm-3, which is above the metal-insulator transition carrier concentration. Experimental characterization techniques used include: transmission electron microscopy, temperature dependent magnetization measurements, Hall effect, resistivity and magnetoresistance measurements. Low-temperature cross-sectional STM and spin-tunneling STM at the Technical University at Eindhoven are used to determine the nature of Mn substitution in InSb and its magnetic properties at the atomic level.Non-technical Description: As to broader impact, alloy films prepared by metalorganic vapor phase epitaxy are provided to colleagues at universities in the US and abroad and Argonne National Laboratories for characterizing their structural, magneto-optical and magnetic properties. An extended collaboration is established between Northwestern University and Technical University of Eindhoven on the imaging of single dopant atom in dilute magnetic semiconductors. The project involves the training of post-doctoral, graduate and undergraduate students in the synthesis and property measurements of ferromagnetic semiconductors. Graduate students are involved in STEM outreach through the HANDS program at the Haven School in Evanston, Illinois. The magnetic semiconductor materials have potential technological importance for spintronic devices such as spin valves, bipolar magnetic junction transistors, spin diode logic circuits and quantum computation devices.

技术描述：III-V 族化合物稀磁半导体 (DMS) 提供了操纵自旋和电荷的潜力，以及一类表现出磁性、磁光和半导体特性的材料。然而，由于磁转变（居里）温度较低，它们的利用受到了阻碍。结果表明，通过金属有机气相外延制备的 InMnSb 合金的居里温度超过 400 K。使用截面扫描隧道显微镜 (STM) 对 Mn 掺杂原子进行成像。没有注意到Mn的聚集，但观察到位置无序。磁性离子在原子尺度上的不均匀分布被认为在磁性行为中起主导作用。本研究项目的目标是确定 DMS 在稀浓度极限下的磁性相图。感兴趣的合金系统是窄带隙 DMS InMnSb。研究了描述无序 DMS 磁特性的理论模型的适用性。要回答的主要问题是（a）为什么这些合金具有高居里温度以及（b）Mn掺杂剂的无序性对转变温度的作用是什么。在该项目中，通过金属有机气相外延沉积外延合金薄膜。合成了Mn浓度低于1%、载流子浓度低于10^19 cm-3的合金。研究了无序在稳定铁磁相中的作用。建议铁磁相在载流子浓度 2 x 10^17 cm-3 处稳定，该浓度高于金属-绝缘体过渡载流子浓度。使用的实验表征技术包括：透射电子显微镜、温度相关磁化测量、霍尔效应、电阻率和磁阻测量。埃因霍温技术大学的低温截面STM和自旋隧道STM用于在原子水平上确定InSb中Mn取代的性质及其磁性能。非技术描述：就更广泛的影响而言，金属有机气相外延制备的合金薄膜提供给美国和国外的大学和阿贡国家实验室的同事，用于表征其结构， 磁光和磁特性。西北大学和埃因霍温技术大学就稀磁半导体中单掺杂原子的成像建立了广泛的合作。该项目涉及对博士后、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。研究生通过伊利诺伊州埃文斯顿避风港学校的 HANDS 项目参与 STEM 推广活动。磁性半导体材料对于自旋电子器件（例如自旋阀、双极磁性结晶体管、自旋二极管逻辑电路和量子计算器件）具有潜在的技术重要性。