Spin physics in Two-Dimensional Layered Ferromagnets

在过去的几十年里，目前可用的电子设备的发展在很大程度上依赖于晶体管的缩小，从而使小型，功能强大的计算机成为我们现代信息社会的基础。摩尔定律有效地描述了每单位面积晶体管数量（和计算能力）的增长，从那以后一直持续着，但这一趋势的终结--晶体管像原子一样小，不能再缩小的时刻--将很快到来。最新智能手机中晶体管的特征长度为7 nm，其中我们只能容纳约14个硅晶体晶格。电子设备使用电子的电荷来操纵它们进行数据处理。这个基本概念需要重新审视现在和全新的计算概念，必须追求和审查，以维持计算效率的进一步增长。自旋电子学的概念创造了一种基于“自旋”的电子技术，有可能取代基于电荷的半导体技术，科学家们已经开始研究新电子学的自旋自由度。自旋电子技术发展的核心是对纳米磁性材料的新发现和理解。磁性材料可以通过其偶极子的方向（从南极指向北极的箭头）存储数字信息。硬盘驱动器有大量的微小磁铁（准确地说是磁畴），它们作为数据存储器，以可靠和廉价的方式保护我们的数字信息。通过对磁特性（所谓的各向异性）和记录介质的反转切换以及开发薄膜多层的可控性的巨大努力，已经实现了磁体中的数据存储的可靠性。自旋电子学进一步构建了更多功能和主动存储器设备，其中通过翻转磁偶极子执行本地数据处理。以非常低的功耗反转偶极子是开发商业上可行的自旋电子器件的关键。要做到这一点，不断努力发现新的磁性材料，并了解其材料特性，是一个有效和有效的方法。在这个项目中，我们将研究一类新的磁性材料，货车德瓦尔斯二维层状铁磁体。它们是石墨烯的磁性版本，石墨烯是单层石墨。铅笔是由石墨制成的，我们可以用铅笔在纸上写字的原因是因为我们在写字时打破了石墨烯片之间的键合，并且在纸上留下了一片破碎的石墨（石墨烯片）。英国科学家发现，当我们小心地打破石墨片时，可以制造单层石墨烯。最重要的是，石墨烯显示出显着的电子特性，而这些特性并不以石墨的形式出现。石墨烯发现后，许多货车范德华材料在单层极限下得到了积极的研究，形成了2D材料的活跃研究领域。2017年，两个独立的研究小组在两种不同的材料中发现了石墨烯的磁性版本，这引起了人们的极大兴趣，但迄今为止对这些材料知之甚少。在这个项目中，我们将研究磁性2D层状材料的基本特性，以回答一些重要的问题，例如“它们与普通的3D磁体不同吗？”如果是这样，它们对我们的自旋电子技术有多大用处？".我们有具体的工作计划来尽可能多地回答这些问题，并探索新型纳米材料的新发现。解决这些问题使我们能够推进目前对2D铁磁性和其中自旋输运的理解，可能导致高效自旋电子存储器的创建。

For the last several decades, the development of currently available electronic devices has relied heavily on the downsizing of the transistor, allowing the technology for the small, powerful computers that are the basis of our modern information society. Moore's Law, effectively describing the growth of the number of transistors per unit area (and computing power), has continued ever since, but the end of that trend - the moment when transistors are as small as atoms, and cannot be shrunk any further - will approaching very rapidly. The characteristic feature length of transistors in latest smart phones is 7 nm, within which we can only fit about 14 lattices of silicon crystals. Electronic devices uses the charge of electrons to manipulate them for data-processing. This fundamental concept needs to be revisited now and radically new computing concepts have to be pursued and examined to sustain the further growth of computation efficiency. The concept of spintronics that creates a "spin"-based electronic technology holds potential to replace the charge-based technology of semiconductors and scientists have begun to examine the spin degree of freedom for new electronics. At the heart of the development of spintronic technologies are new discoveries and understanding of magnetic materials at the nanoscale. Magnetic materials can store digital information by the direction of their dipoles (arrows pointing from South to North poles). Hard disk drives have a vast number of tiny magnets (magnetic domains to be precise) which act as data storages to secure our digital information reliably and cheaply. The reliability of data storage in magnets has been achieved by enormous efforts of understanding magnetic properties (so-called anisotropies) and reversal switching of the recording media as well as developing the controllability of thin-film multi-layers. Spintronics has taken it further to build more functional and active memory devices where local data-processing by flipping magnetic dipoles is performed. Reversing the dipole at a very low power consumption is a key to develop commercially-viable spintronic devices. To do so, continued efforts of discovering new magnetic materials, together with an understanding of their materials properties, is a valid and effective approach. In this project, we will study a new class of magnetic materials, the van der Waals 2D layered ferromagnets. They are a magnetic version of graphene, and graphene is a single layer of graphite. A pencil is made out of graphite and the reason that we can write words on a paper with a pencil is because we break a bonding between sheets of graphene while writing and a broken piece of graphite (sheets of graphene) is left over on the paper. Scientists in the UK discovered that it is possible to make a single layer of graphene when we carefully break graphite sheets. And most importantly, graphene shows remarkable electronic properties which do not show up in the form of graphite. After the discovery of graphene, many van der Waals materials have been actively studied at the monolayer limit, forming the active research field of 2D materials. In 2017, the discovery of a magnetic version of graphene was made in two different materials and by two independent research groups, which attract a great deal of interest but yet not much is so far known about these materials. We will on this project study fundamental properties of magnetic 2D layered materials to answer important questions such as "are they different from normal 3D magnets?", "If so, how useful are they for our spintronic technologies?". We have specific workplans to answer these questions as much as possible and also to explore new discoveries with the novel class of nano-materials. Answering these questions allows us to advance the current understanding of ferromagnetism at 2D and spin transport therein, potentially leading to the creation of highly efficient spintronic memories.