自旋冰异质结的新物理效应及其磁电耦合机制研究

Spin frustration is common in systems with multifold degrees of freedom, e.g. the mutual competition and modulation between spin, lattice, charge, and orbital arouse much exotic physical properties. The type-II multiferroics as novel class of strongly correlated electron systems have been receiving special attentions due to the underlying physics associated with multiferroic order coupling and inter-manipulations. This proposal focuses on the epitaxial spin ice thin film, and is intended to address several major issues of the new physical effect and magnetoelectric coupling mechanism emerged from the low dimensional spin ice, including: (1) Revealing the intrinsic influence of strain, microstructure/magnetic structure of the interface, and magnetic field on the magnetic entropy, spin relaxation, and magnetic monopole excitation. (2) Exploring ferroelectricity and magnetoelectric coupling modulation of spin ice heterostructures under different strains. (3) The multi-order coupling in multiferroics will be extended to other exotic pyrochlore artificial heterostructures. Eventually, novel type-II new multiferroic material and heterostructures in addition to high-performance multiferroic compounds will be synthesized.

自旋失措普遍存在于多种自由度相互竞争的体系，如自旋、晶格、电荷、轨道的相互竞争和调控，诱发很多奇异的丰富物理特性。第II类磁致多铁性因其蕴含丰富的铁性序耦合与调控而成为凝聚态物理关注的研究热点之一。本项目以自旋冰外延薄膜为研究对象，着重揭示和阐明自旋冰在低维下出现的新物理效应及其磁电耦合物理机制，包括：(1) 实现对自旋冰外延薄膜的人工调控，揭示应力、界面微/磁结构、磁场对磁熵、自旋弛豫和磁单极子激发的本征联系；(2) 探索不同应变条件下自旋冰异质结的铁电性和磁电耦合调控；(3) 将自旋序与铁电序耦合延伸到其他具有新奇物理特性的烧绿石多铁人工异质结结构中，在此基础上，发展适应实际应用需求的多铁性新材料和人工异质结。

本项目基本目标是以第II类多铁性体及其异质结为对象，阐明自旋序与铁电序耦合的新物理效应及其机制。虽然具体研究材料体系有差异，但物理目标保持不变。研究工作可简单概括为三句话：(1) 合成四个多铁性新体系。(2) 揭示多铁性材料YMnO3中拓扑畴结构演化机制。(3) 系统总结铁基非常规多铁性体的物理、材料和发展潜力。. 项目执行三年来，在达成项目核心目标方面取得阶段性成果。项目资助下共发表论文7篇，包括PRB (3)、NJP (1)、APL (1)、JAP (1)。同时在J. Phys. D: Appl. Phys.上发表关于铁基多铁性物理与材料的综述论文，正好与本项目主体目标相对应。本项目资助下共培养2名博士生。