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

自石墨烯分离以来，二维（2D）材料家族一直在快速增长，因此在这种低维空间中可以探索的特性范围也在迅速扩大。在这些特性中，磁性已经缺失了很多年，但最近的一项科学突破在2017年推出了第一批原子薄的二维磁性晶体。这些原子级薄的磁铁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=chalcogen）是反铁磁自旋电子学的有趣候选者。基于这些原因，本项目的目的是研究二维反铁磁体（如MnPS3）中的自旋动力学。我们打算通过蒙特卡罗方法和Landau-Lifshitz-Gilbert （LLG）动力学来了解二维晶体的磁性，揭示不同扰动对它们的影响。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)同样考虑不同磁相的材料的畴壁运动；Iii)不同几何形状和结构的退磁场；最后，激光脉冲和脉冲磁场诱导的超快自旋动力学。特别是，MnPS3等材料的自旋特性与晶体结构本质耦合，导致不同的基态、结构和自旋构型。这种独特的行为可以在各种技术应用中得到利用，从辐射硬度、非挥发性和高效磁开关，到超快速写入方案和新的信息标准。然而，在单层AFM磁体的极限下，导致这些独特特征的不同电子量（磁矩、交换、各向异性）之间的相互作用还没有得到很好的理解。本项目旨在通过多尺度方法解决这一挑战。原子性的从头计算将用于了解材料的原子和电子结构的细节，以及获得它们的固有磁性。然后，将在微米尺度上进行磁性和自旋动力学的模拟。Landau-Lifshitz-Gilbert （LLG）动力学将在LLG方程的基础上考虑，考虑到每个原子所经历的有效磁场，LLG方程决定了磁化在固体中的运动。热效应对磁性能的影响可以通过朗之万数学处理来考虑。这是一种行之有效的方法来模拟自旋动力学在不同的维度，系统和组成。我们期望这些微磁模拟将扩大我们对这些磁性材料的理解，直到单层极限，探索它们在记忆存储目的方面的潜在应用。这些见解将代表着向超薄反铁磁自旋电子学迈进了一步。作为这个项目的一部分，我们将与约克大学的VAMPIRE开发人员合作。从这些新方法中获得的任何发展都将被纳入VAMPIRE的正式版本，从而使其可供其他用户使用。

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.