Theory of chiral modulations in confining structures: epitaxial films of cubic helimagnets

最近合成的具有非中心对称B20结构（MnSi， FeGe等）的立方helimages外延薄膜代表了一类新的纳米磁系统，表现出许多在体helimages中未知的物理现象。特别是，立方螺旋成像的纳米层可以观察到20多年前理论上预测的特定粒子样结构（skyrmions），以及通过量子化步骤的场诱导螺旋体展开。我们最近的研究表明，在立方helimages纳米层中，内在手性、结构约束和表面/界面诱导的相互作用之间的相互作用导致了特定的限制性手性调制的形成，这与通常在体helimages中观察到的完全不同。该项目的目的是对受限的手性调制给出一个全面的理论描述，从而建立立方螺旋形纳米层中产生的特定效应与其结构特性之间的物理关系。在标准的helimagitics微磁理论中，我们将在广泛的热力学参数范围内推导出立方helimagies薄层中螺旋调制和skyrmionic调制的严格解。我们的理论发现将用于构建具有不同类型诱导磁各向异性的立方螺旋形纳米层的磁相图。这些结果将应用于最近在MnSi和FeGe外延膜上的实验的详细分析，并阐明在这些系统中观察到的复杂磁化过程。它们也应该为新兴的受限手性调制纳米物理学提供理论基础，并为未来的研究提供实用建议。

Recently synthesized epitaxial thin films of cubic helimagnets with non-centrosymmetric B20 structure (MnSi, FeGe, and others) represent a novel class of nanomagnetic systems exhibiting many physical phenomena unknown in bulk helimagnets. In particular, nanolayers of cubic helimagnets enable the observation of specific particle-like structures (skyrmions) predicted theoretically more than twenty years ago and the field-induced unwinding of helicoids via quantized steps. Our recent studies show that in nanolayers of cubic helimagnets the interplay between intrinsic chirality, structural confinement, and surface/interface induced interactions leads to the formation of specific confined chiral modulations which fundamentally differ from those commonly observed in bulk helimagnets. The aim of the project is to give a comprehensive theoretical description of confined chiral modulations and, thus, to establish physical relations between specific effects arising in cubic helimagnet nanolayers and peculiarities of their structures. Within the standard micromagnetic theory of helimagnetism rigorous solutions for helical and skyrmionic modulations in thin layers of cubic helimagnets will be derived in broad ranges of the thermodynamic parameters. Our theoretical findings will be used to construct magnetic phase diagrams for nanolayers of cubic helimagnets with different types of induced magnetic anisotropy. These results will be applied for detailed analyses of recent experiments in epitaxial films of MnSi and FeGe and to elucidate complex magnetization processes observed in these systems. They also should provide the theoretical basis for the emerging nanophysics of confined chiral modulations and supply practical recommendations for future investigations.