Selective Doping of Antiferromagnetic Semiconductors

反铁磁半导体的选择性掺杂

• 批准号: 0706359
• 负责人: Lian Li
• 金额: --
• 依托单位: University of Wisconsin-Milwaukee
• 依托单位国家: 美国
• 项目类别: Continuing Grant
• 财政年份: 2007
• 资助国家: 美国
• 起止时间: 2007-07-01 至 2011-06-30
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=0706359&HistoricalAwards=false
• 关键词: Selective; Doping; Antiferromagnetic; Semiconductors

Technical: This project aims for synthesis of a room temperature magnetic semiconductor, exploring a new strategy by starting with an antiferromagnetic semiconductor, and preferentially substituting nonmagnetic donors into one sublattice. Current approaches to synthesize these materials focus on doping semiconductors with a transition metal (TM) such as Mn. The magnetic ion is responsible both for providing a localized magnetic moment and a hole (e.g. in GaMnAs). The exchange interaction amongst the localized d electrons of Mn, mediated by the holes, leads to ferromagnetic ordering. In this approach only one type of doping can be obtained, e.g., p-type for Mn doped III-V's, and the concentration required to achieve Curie temperatures above 300K is higher than the solubility of Mn. In this project the approach is to emulate ferromagnetic semiconductors by selective doping of an antiferromagnetic (AFM) semiconductor with nonmagnetic dopants--to preferentially incorporate a nonmagnetic dopant, i.e., Cu, into one of the magnetic sublattices of the AFM semiconductor, resulting in local reduction of the magnetic moment, and in an overall net ferrimagnetic moment. The total magnetization of such doped AFM material is controlled by the number of dopants, and the choice of dopants, so both spin-polarized electrons and holes can be introduced. This approach may evade the problem of solubility limit and permit the independent control of different carrier types in magnetic semiconductors. The scope of earlier research is expanded in this project to investigate the properties of a new class of material: TMGeV2, by varying the group V element (As, P, and Sb) and TM (Cr, Fe, Co, and Ni), through DFT calculations, initially. Guided by the theoretical predictions, experimental efforts will focus on compounds that, when doped, yield ferrimagnetic semiconductors with transition temperature in excess of 300 K and have independently controllable spin-polarized electrons and holes. Epitaxial thin alloy films will be grown by MBE. Their structures will be characterized using high resolution transmission electron microscopy and related diffraction techniques. Magnetic properties will be investigated by temperature and field dependent magnetization measurements, Hall effect and magnetoresistance. Electronic and magnetic properties will be determined by x-ray absorption spectroscopy (XAS) and x-ray magnetic circular dichroism (XMCD) at the Advanced Photon Source, Argonne National Laboratory (ANL). Magnetic domain structures and their evolution will be obtained by scanning electron microscopy with polarization analysis (SEMPA) at the Center for Nanoscale Materials Research, Oak Ridge National Laboratory (ORNL). Non-technical: The project addresses basic research issues in a topical area of electronic/photonic materials science with high technological relevance. It is considered a high risk/high potential pay-off project. If successful, magnetic semiconductors with transition temperature in excess of 300 K and independently controllable carriers will be realized. The project involves training of graduate and undergraduate students in the synthesis and characterization of magnetic semiconductors using facilities at the PI's labs, as well as at ANL and ORNL. The interdisciplinary nature of the research and the combined theoretical/experimental approach provide additional opportunities for graduate and undergraduate students to broaden their educational experience. An RET program will be continued with local high schools to expose high school students to spintronics, and to inspire their interests in science in general.

技术：该项目旨在合成室温磁性半导体，探索一种新策略，从反铁磁半导体开始，优先将非磁性施主替换到一个亚晶格中。目前合成这些材料的方法主要集中在用过渡金属（TM）（例如锰）掺杂半导体。磁性离子负责提供局部磁矩和空穴（例如在 GaMnAs 中）。由空穴介导的 Mn 局域 d 电子之间的交换相互作用导致铁磁有序化。在这种方法中，只能获得一种类型的掺杂，例如 Mn 掺杂的 III-V 族的 p 型，并且实现高于 300K 的居里温度所需的浓度高于 Mn 的溶解度。在该项目中，该方法是通过用非磁性掺杂剂选择性掺杂反铁磁 (AFM) 半导体来模拟铁磁半导体，即优先将非磁性掺杂剂（即 Cu）合并到 AFM 半导体的磁性亚晶格之一中，从而产生局部磁矩和总体净亚铁磁矩的减少。这种掺杂AFM材料的总磁化强度由掺杂剂的数量和掺杂剂的选择控制，因此可以引入自旋极化电子和空穴。这种方法可以避免溶解度极限的问题，并允许独立控制磁性半导体中不同的载流子类型。该项目扩大了早期研究的范围，通过改变 V 族元素（As、P 和 Sb）和 TM（Cr、Fe、Co 和 Ni）来研究新型材料 TMGeV2 的特性，最初通过 DFT 计算。在理论预测的指导下，实验工作将集中于掺杂后可产生转变温度超过 300 K 且具有独立可控自旋极化电子和空穴的亚铁磁半导体的化合物。外延合金薄膜将通过MBE 生长。它们的结构将使用高分辨率透射电子显微镜和相关衍射技术进行表征。将通过温度和磁场相关的磁化测量、霍尔效应和磁阻来研究磁性。电子和磁性特性将通过阿贡国家实验室 (ANL) 先进光子源的 X 射线吸收光谱 (XAS) 和 X 射线磁圆二色性 (XMCD) 来测定。磁畴结构及其演变将通过橡树岭国家实验室（ORNL）纳米材料研究中心的偏振分析扫描电子显微镜（SEMPA）获得。非技术性：该项目解决具有高度技术相关性的电子/光子材料科学主题领域的基础研究问题。它被认为是一个高风险/高潜在回报的项目。如果成功，将实现转变温度超过 300 K 且载流子独立可控的磁性半导体。该项目涉及使用 PI 实验室以及 ANL 和 ORNL 实验室的设施对研究生和本科生进行磁性半导体合成和表征方面的培训。该研究的跨学科性质和理论/实验相结合的方法为研究生和本科生提供了额外的机会来扩大他们的教育经验。当地高中将继续开展 RET 项目，让高中生接触自旋电子学，并激发他们对科学的兴趣。