Two-Dimensional Magnetic Materials for the Next Generation of Functional Device Platforms (2DMagnete)

磁性可能是已知的最古老的完全起源于量子力学的物理现象。从William Gilbert在他1600年的专著《de Magnete》中进行的早期研究，到目前使用自旋电子学概念的磁铁硬盘驱动器技术，在真正的二维(2D)磁铁的磁性极限上，仍有几个悬而未决的问题。这是70多年前路易斯·内尔、列夫·兰道或拉尔斯·昂萨格等该领域的先驱们指出的一个内在问题，但至今仍没有合理的解决方案。如今，随着不同的计算模拟技术和实验方法的出现，我们有机会在真正的现场基础上解决这个具有基本和技术影响的前沿问题。2017年在单层半导体晶体(例如CrI3)中发现2D磁性和观察与层相关的磁相(例如反铁磁或铁磁)方面的突破开辟了基础科学和器件技术的新范式。这些化合物具有巨大的磁电子学潜力，以及将逻辑和存储器结合在一起进行高性能计算。一个改变游戏规则的想法是，将集成的2D磁体开发到选定的矩阵中，作为具有定制功能的智能混合动力车。这种轻质材料将在电磁干扰屏蔽(例如减少电磁污染)、低能量数据存储(例如更好的硬盘驱动器)和超低功率开关(例如更智能的健康监测传感器)方面具有变革性的应用。它们的原子稀薄特性还将使人们能够通过非磁性手段，如通过电场或机械应变来前所未有地操纵磁性。这些磁体的范德华(VDW)特性使异质结和器件的任意设计成为可能，没有晶格匹配的限制，无论是在不同的磁体之间，还是在磁体和其他2D材料之间。根据诺贝尔奖获得者安德烈·K·盖姆的说法，“可能的VDW结构的选择只受我们的想象力的限制。”因此，2D磁体的发现与界面工程能力相结合，以前所未有的控制和新的功能，在磁性的基础上开辟了新的天地。在这个项目中，我们将：(1)提出有重点的理论发展，以阐明本征VDW材料的磁性对器件平台的突破性进展。这是由一个终极问题引发的：“原子层材料的磁性极限是多少，以及如何操纵它？”人们寻找已久但最近才发现的真正的2D磁性材料，可能会在信息数据的获取、理解和存储方式上带来一场革命。它们是如何工作的完全是未知的。我们的目标是展示这种现象是如何发生的，以及如何控制它。这样做将弥合一种全新的磁性材料在有限温度下跨越不同长度尺度的差距。这将导致对低维磁体及其与光学和电子学以廉价和可行的方式在超紧凑型自旋电子学中集成的理解方面的科学突破。(2)要做到这一点，我们需要采取三个步骤：i)开发并将高通量技术应用于量子力学模拟，以预测在与技术相关的温度下能够真正成为2D磁体的最佳材料；ii)对我们的模型进行基准测试，以跨不同维度-原子(几个？？S)、介观(几纳米)和宏观(数百微米)-来弥合2D磁现象的修改；以及，最后，iii)研究磁性与外部驱动力(电/磁、应变、界面)之间的相互作用，以使用多尺度方法获得磁控制。在技术上，我们的建议将为2D磁体的材料设计铺平道路，并远远超出目前可能在磁性设备上进行数据存储的应用。

Magnetism is perhaps the oldest known physical phenomenon of entirely quantum mechanical origin. From the early studies performed by William Gilbert in his 1600 monograph De Magnete, through to current magnet hard-drive technology using spintronics concepts, several open questions still remain on the limit of magnetism at truly two-dimensional (2D) magnets. This is an intrinsic problem pointed out more than 70 years ago by pioneers in the field such as Louis Néel, Lev Landau or Lars Onsager but still without a plausible solution. Nowadays with the advent of different computational simulation techniques, and experimental approaches, we have the opportunity to tackle this cutting-edge problem with fundamental and technological implications in a real live-basis. The 2017 breakthroughs in discovery of 2D magnetism in monolayer semiconductor crystals (e.g. CrI3) and observation of layer-dependent magnetic phases (e.g. antiferromagnetic or ferromagnetic) open up new paradigms in fundamental science and device technologies. These compounds have enormous potential for magneto-electronics, as well as combining logic and memory for high-performance computing. One game-changing idea is to develop integrated 2D-magnets into selected matrices as smart hybrids with tailored functionalities. Such lightweight materials will have transformative applications in electromagnetic interference shielding (e.g. reduce electromagnetic pollution), low-energy data storage (e.g. better hard-drives), and ultralow-power switching (e.g. smarter health monitoring sensors). Their atomically thin nature will also enable unprecedented manipulation of magnetic properties by non-magnetic means, such as via electric fields or mechanical strain. The van der Waals (vdW) nature of these magnets enables arbitrary design of heterojunctions and devices, without lattice-matching constraints, formed either between different magnets or between magnets and other 2D materials. According to Nobel laureate Andre K. Geim, "the choice of possible vdW structures is limited only by our imagination". Thus, the discovery of 2D magnets combined with interfacial engineering capabilities breaks new ground in the fundamentals of magnetism, with unprecedented control and new functionality. In this project we will: (1) propose focused theory developments to elucidate the magnetic properties of intrinsic vdW materials to groundbreaking advances in device platforms. This is triggered by the ultimate question: "What is the limit of magnetism in an atomic layer material and how to manipulate it?" Long-searched but only recently discovered, truly 2D magnetic materials could enable a revolution on how information data is accessed, understood and stored. How they work is completely unknown. We aim to show how this phenomenon occurs and how to control it. Doing so would bridge the gap across different length scales at finite temperature of a radical new class of magnetic materials. This will lead to a scientific breakthrough in the understanding of low-dimensional magnets and their integration with optics and electronics in a cheap and feasible way in ultra-compact spintronics. (2) To do this we have three steps to take: i) to develop and apply high-throughput techniques to quantum mechanical simulations to predict the best materials that can be truly 2D magnets at temperatures of technological relevance; ii) to benchmark our modelling across different dimensionalities - atomistic (few Å's), mesoscopic (several nm's) and macroscopic (hundreds of micrometer's) - to bridge the modifications of the magnetic phenomena at 2D; and, finally, iii) to investigate the interplay between magnetic properties with external driving forces (electric/magnetic, strain, interfaces) to obtain magnetic control using multiscale methods. Technologically, our proposal would pave the way to materials design of 2D-magnets and goes well beyond the currently possible applications of data storage on magnetic device.