Non-Local Chiral Interactions In Corrugated Magnetic Nanoshells

有一个方面是大多数具有根本吸引力和技术相关的新型磁性材料的共同之处，即它们的非共线磁性织构，如自旋螺旋线、手性磁场壁或Skyrmions。这些织构通常是依靠Dzyaloshinskii-Moriya相互作用(DMI)实现的，这种相互作用存在于某些偏心磁性晶体中。最近，曲率效应作为一种新的手段，通过依赖于外在参数，如薄膜的几何形状，来设计手性磁性。虽然这是一个非常新的研究领域，但目前，从新的基础物理和应用装置的思想来看，曲面的拓扑已经得到了广泛的探索。目前对磁场的理解仅限于超薄磁性薄膜的情况，其中曲率产生了两种截然不同的效应，这两种效应源于出现的手征和各向异性相互作用。在这个极限下，所有曲率诱导的手征效应都必须是局域的。即使在薄膜厚度的主近似中的非局部静磁效应也被归结为能量泛函中的局部各向异性项。在这里，我们的目的是通过建立一个微磁框架来解释薄膜厚度的下一个数量级，从而扩展对弯曲几何中磁性的基本理解。我们的理论预测表明，在厚度的第二阶，非局域静磁效应导致了非局域手征效应的出现。这些非局域手性相互作用与由界面诱导或整体DMI引起的局域效应的标准情况有很大的不同。这些非局域手征效应既没有从理论上研究，也没有从实验上研究。该项目的主要目标是与理论(基辅大学Sheka教授小组)和实验(基尔大学McCord教授小组，以及Makarov博士、Helmholtz-Zentum Dresden-Rossendorf博士小组)一起努力调查这一新的效应。理论上，我们将探索由于表面和体积静磁电荷之间的耦合(对于平板薄膜，这种耦合必然是不存在的)手性相互作用源的预测存在。在实验上，我们将通过研究波纹铁磁壳中磁区的静力学和迁移率来验证这些理论预测。这将通过在具有可调几何特征(波纹相对于其周期的幅度)的曲率模板上沉积我们的面外磁化薄膜来制备。关键的挑战是找到新效应的指纹，例如通过监测即使在剩磁时磁畴壁相对于条纹轴线的倾斜，并找到一种方法来量化这种效应的强度。这个项目将加深我们对凝聚态中曲率效应的理解，有助于将新的理论概念转化为实际的实验观测。

There is one aspect, which is in common to the majority of fundamentally appealing and technologically relevant novel magnetic materials, namely their non-collinear magnetic textures like spin spirals, chiral domain walls or skyrmions. These textures are typically achieved relying on the Dzyaloshinskii-Moriya interaction (DMI), which is present in certain acentric magnetic crystals. Recently, curvature effects emerged as a novel mean to design chiral magnetic properties by relying on extrinsic parameters, e.g. geometry of thin films. Although this research field is very new, at present, the topology of curved surfaces is broadly explored with respect to new fundamental physics as well as applied device ideas. The present understanding of the field is limited to the case of ultrathin magnetic films, where curvature brings about two distinct effects stemming from emergent chiral and anisotropy interactions. In this limit, all curvature-induced chiral effects are necessarily local. Even non-local magnetostatic effects in the main approximation on the film thickness are reduced to local anisotropy terms in the energy functional.Here, we aim to extend the fundamental understanding of magnetism in curved geometries by developing a micromagentic framework accounting for the next orders in the film thickness. Our theoretical predictions show that in the second order on thickness, non-local magnetostatics results in the emergence of the non-local chiral effects. These non-local chiral interactions are very different compared to the standard case of local effects stemming from interface-induced or bulk DMI. These non-local chiral effects are studied neither theoretically nor experimentally. The key objective of this project is to join the efforts of theoretical (group of Prof. Sheka, University of Kyiv) and experimental (groups of Prof. McCord, University of Kiel, and Dr. Makarov, Helmholtz-Zentrum Dresden-Rossendorf) teams on the investigation of this novel effect. Theoretically, we will explore the predicted existence of novel source for chiral interactions due to the coupling between surface and volume magnetostatic charges (this coupling is necessarily absent in the case of flat films). Experimentally, we will target validation of these theoretical predictions by studying the statics and mobility of magnetic domains in corrugated ferromagnetic shells. Those will be fabricated by deposition of our-of-plane magnetized thin films on curvature templates with tunable geometric characteristics (amplitude of corrugation with respect to its period). The key challenge is to find a fingerprint of the novel effect, e.g. by monitoring the tilt of magnetic domain wall with respect to the stripe axis even at remanence, and find a method, which will allow quantification of strength of this effect.This project will deepen our understanding on the curvature effects in condensed matter help to turn the novel theoretical concepts into real experimental observables.