2D materials based ultra-thin memory storage: efficient energy conversion and novel device platforms

自从分离出石墨烯以来，二维(2D)材料的家族一直在快速增长，因此可以在这种低维空间中探索的一系列性质也在快速增长。在这些性质中，磁性已经消失了很多年，但最近的一项科学突破在2017年推出了第一个2D原子薄磁性晶体。这些原子薄的磁体在自旋电子学领域有潜在的应用。特别是，过渡金属硫代磷酸盐，如MnPX3(其中X=硫族)是反铁磁自旋电子学有趣的候选者。基于这些原因，本项目的目的是研究二维反铁磁体(如MnPS3)的自旋动力学。我们打算通过蒙特卡罗方法和Landau-Lifshitz-Gilbert(LLG)动力学来理解2D晶体的磁性，并揭示不同微扰对它们的影响。这意味着对低维系统的自旋动力学的描述，包括i)不同温度和材料厚度下的磁畴；ii)这类材料中也考虑不同磁相的磁区壁运动；iii)不同几何和结构的退磁场；以及iv)激光脉冲和脉冲磁场诱导的超快自旋动力学。特别是，像MnPS3这样的材料中的自旋特征本质上与晶体结构耦合，导致不同的基态、结构和自旋组态。这种独特的行为可以在各种技术应用中得到利用，从抗辐射、非易失性和有效的磁开关，到超快写入方案和新颖的信息标准。然而，在单层AFM磁体的极限下，不同的电子量(磁矩、交换、各向异性)之间的相互作用对这些独特的特征并不是很好的理解。该项目打算通过多尺度方法来应对这一挑战。将进行原子从头计算，以了解材料的原子和电子结构的细节，以及获得它们的本征磁性。然后，将在微米尺度上进行磁性和自旋动力学的模拟。基于LLG方程，我们将考虑Landau-Lifshitz-Gilbert(LLG)动力学，该方程考虑了每个原子所经历的有效磁场，从而确定了固体中磁化的运动。通过朗之万数学处理，可以考虑热效应对磁性的影响。这是一种成熟的方法来模拟不同维度、系统和组成的自旋动力学。我们希望这些微磁模拟将扩大我们对这些磁性材料的理解，甚至达到单分子层的极限，探索它们在存储记忆方面的潜在应用。这些见解将代表着向超薄反铁磁自旋电子学迈出的一步。作为这个项目的一部分，我们将与约克大学的吸血鬼开发者合作。来自这些新方法的任何开发都将被合并到官方版本的吸血鬼中，从而使其他用户可以使用它们。

The family of two-dimensional (2D) materials has been growing fast since the isolation of Graphene, and so has the range of properties that can be explored in this low-dimensionality. Among such properties, magnetism was missing for a number of years, but a recent scientific breakthrough has introduced the first 2D, atomically thin, magnetic crystals in 2017. These atomically thin magnets find potential applications in the field of spintronics. In particular, transition metal thiophosphates such as MnPX3 (where X=chalcogen) are interesting candidates for antiferromagnetic spintronics. For these reasons, the aim of this project is to study the spin dynamics in 2D antiferromagnets such as MnPS3. We intend to understand the magnetic properties of 2D crystals and unveil the effect of different perturbations on them through Monte Carlo methods and Landau-Lifshitz-Gilbert (LLG) dynamics. This implies a description of the spin dynamics of systems with low dimensionality, including i) magnetic domains at different temperatures and material thicknesses; ii) domain wall motion in such materials, also considering different magnetic phases; iii) demagnetizing fields at different geometries and structure; and finally, iv) ultrafast spin dynamics induced by laser pulses and pulsed magnetic fields. In particular, the spin features in materials such as MnPS3 are intrinsically coupled to the crystal structure, resulting in different ground states, structures and spin configurations. This distinctive behaviour can be exploited in a variety of technological applications ranging from radiation-hardness, non-volatility, and efficient magnetic switching, up to ultra-fast writing schemes and novel information standards. Nevertheless, the interplay between different electronic quantities (magnetic moment, exchange, anisotropy) responsible for these unique features is not well understood at the limit of a single layer AFM magnet. This project intends to tackle this challenge through a multi-scale approach. Atomistic ab-initio calculations will be carried out to understand details of the atomic and electronic structure of the materials, as well as obtaining their intrinsic magnetic properties. Then, simulations of magnetic properties and spin dynamics will be performed at the micro-meter scale. Landau-Lifshitz-Gilbert (LLG) dynamics will be considered, based on the LLG equations, which determine the motion of the magnetisation in a solid considering the effective magnetic field as experienced by each atom. Thermal effects on the magnetic properties can be included through a Langevin mathematical treatment. This is a well-established approach to simulate spin dynamics at different dimensionality, systems and compositions. We expect that these micromagnetic simulations will broaden our understanding of these magnetic materials down to the monolayer limit, exploring their potential applications for memory storage purposes. Such insights will represent a step forward towards ultrathin antiferromagnetic spintronics. As part of this project, we will collaborate with the developers of VAMPIRE at the University of York. Any developments derived from these new approaches will be incorporated in the official version of VAMPIRE, thus making them available to other users.