Half-Metallic Semiconducting Magnets with Gapless Dispersion and Antiferromagnetism

开发结合了电子的磁性的新型电子设备是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”目前正在对信息技术的电子设备产生重大影响。1988年，在一种新的合成材料中取得了一项关键发现，在这种材料中，一个小磁场可以产生巨大的电阻变化，这种效应被称为巨磁电阻。这种微小的混合结构允许使用小得多的磁性数据存储设备(硬盘驱动器)。1995年，又发现了另一种磁阻器件，也是一种合成的混合结构，但这种器件依赖于量子力学隧道效应。这种奇异的隧道效应可以想象为一个粒子与墙相撞，然后突然在另一边重新出现。这种基于自旋的现象目前被用于安装在所有计算机中的存储设备中，并且也被并入磁随机存取存储器(MRAM)中。当今该领域的突出问题之一是建立能够产生具有预定南北磁取向的载流电子的新设备。该研究奖致力于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。这些基于自旋的设备的科学和工程的进一步发展有望推动未来的应用，这些应用是低功率、高速、高密度的，并最终在信息处理方面具有成本效益。拟议的方法有望为新材料和设备打开大门，这些材料和设备具有前所未有的有用特性。这项研究的广泛影响是通过在电子、磁性和光学纳米结构领域对年轻人进行教育和培训来确保的，这些领域对发展未来的信息技术应用至关重要。最近预测了一种新的材料类别，它融合了半金属磁体和半导体的特性。理论能带结构计算表明，这些逆Heusler材料在电子自旋的一个方向上有一个费米能隙，而在另一个电子自旋方向上，价带边和导带边在费米能区相交。这些用于器件的自旋无隙半导体(SGS)的一大优势依赖于简单的栅极电压就可以调节自旋特性的特性。此外，这些逆Heusler材料包括半金属反铁磁体(HMAF)，它是自旋极化的，但不是磁性的。SGS和HMAF材料的新功能将利用一些新的和有价值的特性，即使在室温下也是如此。这些有价值的资产包括：半金属高自旋极化(~100%)；产生自旋极化的空穴和自旋极化的电子；电压可调的自旋极化；以及没有边缘磁场的自旋极化的HMAF。到目前为止，已有数十种反向Heusler材料被预测具有SGS性质。其中包括磁性Mn2CoAl和反铁磁性Mn3Al。到目前为止，只合成了几种材料：如块体Mn2CoAl和Fe2CoSi，以及制备和研究薄膜的第一个主要步骤(在GaAs上外延Mn2CoAl)。本论文主要研究了利用分子束外延和溅射技术合成含这些X2YZ四亚晶格材料的薄膜器件。多层器件将用电压栅来改变费米能量相对于自旋极化的导带和价带。将制作隧道结来研究自旋自由度。合作者包括来自几所大学以及国家同步加速器和中子实验室的研究人员。这笔赠款由电气、通信和网络系统司(ECCS)的电子、光子学和磁性设备(EPMD)计划以及材料研究部(DMR)的电子和光子材料(EPM)计划联合资助。

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).