磁斯格明子晶格相组织和相变行为的热力学和动力学研究

Magnetic skyrmions are topologically non-trivial, quasi-particle spin textures. Due to their nanometric sizes, unique emergent electrical and magnetic properties, skyrmions are widely considered as one of the most promising information carriers in the next generation magnetic storage technique which should have high-speed, high-density, low-energy-cost and non-volatile features. While the single-particle properties of skyrmions have been fully investigated, the understandings on their collective behaviors are still lacking. In single crystal skyrmion-hosting materials, skyrmions form two-dimensional hexagonal lattices. Although the transitions between a skyrmion lattice and some meta-stable states or other magnetically ordered states with trivial topology have been studied, the equilibrium phase behaviors and phase transitions of skyrmion lattices have rarely been reported until now. This project intends to investigate the phase behaviors and phase transitions of skyrmion lattices via the combination of in-house measurements, small angle neutron scattering and in situ Lorentz transmission electron microscopy. Specifically, this project intends to manipulate the phase bahaviors of skyrmion lattices, and further to induce phase transitions in these lattices, via the tuning of temperature, magnetic field, electric currents and electric fields. Special focuses will be given on the investigations of the macroscopic properties, microscopic mechanism, the critical behaviors and the belonging universality class of those phase transitions, and the dynamics of topological defects during those phase transition. This project will deepen and extend our understandings on the thermodynamic and dynamic properties of skyrmion lattices.

磁斯格明子是拓扑非平凡的自旋涡旋准粒子激发，因具有纳米量级的尺寸，奇异的电学磁学性质，被广泛认为是实现下一代高速、高密度、低能耗及非易失性磁存储技术的关键信息单元之一。尽管对斯格明子的单体行为已有充分认识，但对其集体行为的研究尚在起步阶段。例如在单晶体系中，斯格明子会形成二维六角晶格，目前的研究仅报道了该晶格与亚稳态或与其他磁有序相之间的转变，对该晶格本身的平衡态相和相变行为研究还非常罕见。本项目拟通过结合宏观物性测量、小角中子散射和实空间实时原位洛伦兹透射电镜成像等实验手段，研究斯格明子晶格的相组织和相变行为。具体而言，将通过改变温度、磁场、电流、电场等手段，调制斯格明子晶格的相组织，并进一步诱导其产生相变，着重讨论这些相变的宏观性质、微观机制、临界行为的普适类以及相变过程中拓扑缺陷的动力学等。本项目将有助于加深拓宽对斯格明子晶格热力学和动力学的理解。

磁斯格明子是拓扑非平凡的自旋涡旋准粒子激发，因具有纳米量级的尺寸，奇异的电学磁学性质，被广泛认为是实现下一代高速、高密度、低能耗及非易失性磁存储技术的关键信息单元之一。尽管对斯格明子的单体行为已有充分认识，但对其集体行为的研究尚在起步阶段。例如在单晶体系中，斯格明子会形成二维六角晶格，此前的研究仅报道了该晶格与亚稳态或与其他磁有序相之间的转变，对该晶格本身的平衡态相和相变行为研究还非常罕见。本项目主要通过实空间实时原位洛伦兹透射电镜成像方法，并结合宏观物性测量、小角中子散射等实验手段，实现了二维斯格明子晶格的可控熔化相变，发现了新的斯格明子凝聚相，并对该相变进行了详细的定量表征，给出了相变的微观机制：即研究了各个凝聚相中粒子的排布形式，得到了系统的空间和时间关联函数、关联长度、粒子间相互作用等在各个凝聚相中随外场的演化，以及相变过程中拓扑缺陷的热力学和动力学行为。还实现了电场对斯格明子相的局域相调控。本项目的成果将有助于加深拓宽对斯格明子晶格热力学和动力学的理解，也将为其在自旋电子学方面的应用提供基础。

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