Half-Metallic Semiconducting Magnets with Gapless Dispersion and Antiferromagnetism

开发新的电子器件，结合电子的磁特性是在设备工程和纳米技术的前沿。基于自旋的电子学或"自旋电子学"目前对用于信息技术的电子设备具有巨大影响。1988年在一种新的合成材料中有了一个关键的发现，在这种材料中，一个小磁场可以产生电阻的大变化，这种效应称为巨磁阻。这种微小的混合结构允许更小的磁性数据存储设备（硬盘驱动器）。1995年，另一种磁致电阻器件被发现，这也是一种合成的混合结构，但这种器件依赖于量子力学隧穿。这种奇特的隧穿可以想象成一个粒子与墙相撞，然后突然出现在另一边。这种基于自旋的现象目前用于安装在所有计算机中的存储器设备中，并且也被纳入磁性随机存取存储器（MRAM）中。 目前，该领域的一个突出问题是构建能够产生具有预定南北磁取向的载流电子的新器件。该研究奖的重点是开发合成多层半导体结构，通过施加简单的输入电压来控制电子的磁取向。推进这些基于自旋的器件的科学和工程有望推进未来的应用，这些应用是低功耗，高速度，高密度，并最终具有成本效益的信息处理。预计所提出的方法将为具有以前从未考虑过的有用特性的新材料和设备打开大门。这项研究的广泛影响是通过教育和培训年轻人在电子，磁性和光学纳米结构领域，这是至关重要的开发未来的应用在信息技术。理论能带结构计算表明，这些反Heusler材料的费米能级在电子自旋的一个方向上位于带隙中，而在电子自旋的另一个方向上，价带边和导带边在费米能级处相遇。这些自旋无隙半导体（SGS）用于器件的最大优点之一依赖于其中简单的栅极电压可以调谐自旋性质的性质。此外，这些反赫斯勒材料包括自旋极化但非自旋的半金属反铁磁体（HMAF）。SGS和HMAF材料的新功能将利用几个新的和有价值的性能，即使在室温下。这些宝贵资产包括：半金属高自旋极化（~100%）;自旋极化空穴以及自旋极化电子的产生;电压可调自旋极化;以及没有边缘磁场的自旋极化HMAF。到目前为止，已经预测了几十种逆赫斯勒材料具有SGS特性。这些包括磁性Mn2CoAl和反铁磁性Mn3Al。 到目前为止，只有少数材料被合成：如块状Mn2CoAl和Fe2CoSi;以及合成和研究薄膜的第一个主要步骤（GaAs上的外延Mn2CoAl）。研究的重点是合成薄膜器件，将这些X2YZ四亚晶格材料使用MBE和溅射。多层器件将与电压门制造，以改变相对于自旋极化的导带和价带的费米能。隧道结将被制作用于研究自旋自由度。合作者包括来自几所大学和国家同步加速器和中子实验室的研究人员。该补助金由电气，通信和网络系统（ECCS）部门的电子，光子学和磁器件（EPMD）计划以及材料研究（DMR）部门的电子和光子材料（EMPs）计划共同资助。

Developing new electronic devices that incorporate the electron's magnetic properties is at the forefront of device engineering and nanotechnology. Spin-based electronics or "spintronics" is currently having a great impact on electronic devices for information technology. A key discovery was made in 1988 in a new synthetic material, where a small magnetic field could produce a large change in resistance, an effect called Giant Magnetoresistance. This tiny hybrid structure allowed for much smaller magnetic data storage devices (hard disk drives). In 1995 another magnetoresistive device was discovered, that was again a synthetic hybrid structure, but this device relied on quantum mechanical tunneling. Such exotic tunneling can be imagined as a particle colliding with a wall and suddenly reappearing on the other side. This spin-based phenomenon is currently used in memory devices installed in all computers and is also being incorporated in magnetic random access memories (MRAM). One of the outstanding issues today in this field is to build new devices that can produce current-carrying electrons that have a predetermined North-South magnetic orientation. This research award is focused on developing synthetic multilayer semiconductor structures for controlling the electron's magnetic orientation by applying a simple input voltage. Furthering the science and engineering of these spin-based devices is expected to advance future applications that are low-power, high-speed, high-density, and eventually cost effective for information processing. The proposed approach is expected to open doors to new materials and devices having useful properties never before contemplated. Broad impact of this research is assured by educating and training young people in the areas of electronic, magnetic and optical nanostructures that are crucial for developing future applications in information technology.A novel class of materials has recently been predicted that merge the properties of half-metallic magnets and semiconductors. Theoretical band structure calculations show that these inverse Heusler materials have a Fermi energy lying in a gap for one direction of electron spin, but for the other direction of electron spin the valence and conduction band edges meet at the Fermi energy. One of the great advantages of these spin gapless semiconductors (SGS) for devices relies on the property where a simple gate voltage can tune the spin properties. Furthermore, these inverse Heusler materials encompass half-metallic antiferromagnets (HMAF) that are spin-polarized but nonmagnetic. New functionalities of SGS and HMAF materials would take advantage of several novel and valuable properties, even at room temperature. These valuable assets include: half-metallic high spin polarization (~100 %); generation of spin-polarized holes as well as spin-polarized electrons; voltage-tunable spin polarization; and spin-polarized HMAF without fringing magnetic fields. Thus far, several dozen inverse Heusler materials have been predicted to have SGS properties. These include magnetic Mn2CoAl and antiferromagnetic Mn3Al. Up to now, only a few materials have been synthesized: such as bulk Mn2CoAl and Fe2CoSi; and the first major step to synthesize and investigate thin films (epitaxial Mn2CoAl on GaAs). The research focuses on the synthesis of thin film devices incorporating these X2YZ four-sublattice materials using MBE and sputtering. Multilayer devices will be fabricated with voltage gates in order to vary the Fermi energy with respect to the spin-polarized conduction and valence bands. Tunnel junctions will be fabricated for investigating the spin degrees of freedom. Collaborators include researchers from several universities, and national synchrotron and neutron laboratories. This grant is funded jointly by the Electronics, Photonics, and Magnetic Devices (EPMD) Program in the Division of Electrical, Communications and Cyber Systems (ECCS) and by the Electronic and Photonic Materials (EPM) Program in the Division of Materials Research (DMR).