Spin excitations in ultrathin metallic films

该项目包括两个分项目。(a)具有自发Skyrmion晶格的SiO2薄膜中的自旋激发：在SiO2衬底上生长的SiO2薄膜的界面处，平移对称性被破坏。在存在大的自旋-轨道耦合的情况下，平移对称性的缺失导致非零反对称交换相互作用，称为Dzyaloshinskiii-Moriya（DM）相互作用。这种反对称交换相互作用可以稳定具有旋转结构的手征自旋织构，称为skyrmion。Skyrmions由于其有趣的物理性质以及在自旋电子学中的潜在应用，在过去的几年里引起了人们的广泛关注。Skyrmion的一个有希望的应用是在所谓的Skyrmion赛道存储器中，其想法是使用Skyrmion作为位。详细的skyrmion动力学知识是非常可取的进一步发展这样的存储器设备。磁性固体中的自旋动力学通常用基本集体磁激发（磁振子）来描述。在另一方面，为了理解skyrmion的动力学，磁振子-skyrmion相互作用的实验研究是特别重要的。这个项目的想法是激发在Ir（111）上生长的铁磁薄膜中形成的纳米skyrmionic晶格中的磁振子，并研究系统的动力学。(b)原子尺度磁振子晶体的设计：在新兴的磁振子领域，中心思想是使用基本集体磁激发（磁振子）来编码或传输信息。实现这一想法的第一步是设计一种介质，在这种介质上可以激发不同的磁振子模式。磁振子覆盖的能量（频率）范围相当广，从几十千兆赫到几百太赫兹。磁振子的群速度取决于它们的能量（能量越高，磁振子越快）。为了在磁振子学中使用超快（太赫兹）磁振子，第一步是设计一个模板，在该模板上可以激发和操纵不同的磁振子模式。因此，需要一种新的太赫兹磁振子材料设计方法。我们的想法是提出一种基于多层薄膜的原子尺度太赫兹磁振子晶体的设计方法。该项目的中心点是设计磁性多层膜，由铁磁金属的交替原子层组成，其中可以有效地激发不同的磁振子模式。在下一步中，我们的目标是提供一种通过改变材料组合和原子层数目来调谐磁振子带结构的方法。研究结果将对设计用于太赫兹磁振子、太赫兹电磁传感器和太赫兹微波滤波器的材料产生影响。

The project consists of two subprojects. (a) Spin excitations in ultrathin films with a spontaneous skyrmion lattice: At the interface of an ultrathin film grown on a nonmagnetic substrate the translational symmetry is broken. The absence of the translational symmetry in the presence of a large spin-orbit coupling leads to a non-zero antisymmetric exchange interaction, known as Dzyaloshinskii-Moriya (DM) interaction. This antisymmetric exchange interaction can stabilize a chiral spin texture with whirling structures, known as skyrmion. Skyrmions have attracted lots of attentions during the last few years because of their interesting physics and also their potential applications in spintronics. One of the promising applications of skyrmions is in the so called skyrmion racetrack memory where the idea is to use a skyrmion as a bit. A detailed knowledge on skyrmion dynamics is highly desirable for further development of such memory devices. The dynamics of spin in a magnetic solid is usually described in terms of elementary collective magnetic excitations (magnons). In other to understand the dynamics of skyrmions the experimental investigations on magnon-skyrmion interaction are of particular fundamental interest. The idea of this project is to excite magnons in a nano-skyrmionic lattice formed in an ultrathin Fe film grown on Ir(111) and investigate the dynamics of the system. (b) Design of atomic scale magnonic crystals: In the emerging field of magnonics, the central idea is to use the elementary collective magnetic excitations (magnons) for encoding or transmitting information. The first steptowards realization of this idea is to design a medium on which different magnon modes can be excited. The medium should also provide a way of tuning the magnon band structure as it is desired.Magnons cover a rather wide range of energy (frequency) spectrum, starting from a few tenth of gigahertz up to hundreds of terahertz. The magnons group velocity depends on their energy (the higher the energy, the faster the magnons). For using ultrafast (terahertz) magnons in magnonics the first step is to design a template on which different magnon modes can be excited and manipulated. Therefore a new approach of materials design for terahertz magnonics is highly demanded. Our idea is to suggest a way of designing atomic scale magnonic crystals for terahertz magnonics based on multilayer thin films. The central point of this project would be to design magnetic multilayers, composed of alternating atomic layers of ferromagnetic metals, in which different magnon modes can be efficiently excited. In the next step we aim to provide a way of tuning the magnon band structure via changing the materials combination and the number of atomic layers. The results shall have an impact on the design of materials useful for terahertz magnonics, terahertz electromagnetic sensors and terahertz microwave filters.