Mechanisms for multiferroicity in rare-earth orthoferrites: Role of the Dzyaloshinskii-Moriya interaction

该项目的目的是确定多铁性材料中磁性和铁电有序参数之间耦合的微观机制，其中铁电性是由磁性有序（ii型多铁性）引起的。将特别注意阐明反对称Dzyaloshinskii-Moriya （DM）相互作用的作用，该相互作用被认为是负责多铁性的主要组成部分之一。澄清磁性和铁电序参数之间耦合的起源将允许创建具有所需性能的新功能材料。我们计划研究稀土正铁氧体RFeO3 （R = Ho, Dy, Lu， Tb和Tm）的晶体和磁性结构以及磁相互作用。计划将各种中子散射技术应用于RFeO3族成员的晶体和磁性研究。利用偏振中子衍射，包括独特的球形中子偏振技术和经典的翻转比方法，研究其复杂磁结构的特殊性及其在温度、磁场和电场等外部条件下的演变。磁动力学的研究将通过非弹性中子散射进行，这允许获得磁交换相互作用参数。对RFeO3晶体结构的详细研究，即寻找弱铁磁相中的结构畸变，以证明预期的对称性降低，将通过非极化中子和x射线衍射技术以及膨胀测量来完成。所提出的实验研究结果将与这些材料的铁电相进行分析。在此基础上，建立了影响正铁氧体多铁性的磁电相互作用模型，并建立了该模型的通用性。

The aim of this project is to determine the microscopic mechanisms responsible for the coupling between the magnetic and ferroelectric order parameters in multiferroic materials, where ferroelectricity is induced by magnetic ordering (type-II multiferroics). Particular attention will be paid to the elucidation of the role of the antisymmetric Dzyaloshinskii-Moriya (DM) interaction which is considered to be one of the main components responsible for the multiferroicity. Clarification of the origin of the coupling between the magnetic and ferroelectric order parameters would allow to create new functional materials with desired properties.We plan to study the crystal and magnetic structures and magnetic interactions in rare-earth orthoferrites RFeO3 (R = Ho, Dy, Lu, Tb and Tm). Various neutron scattering techniques are planned to be applied for the investigation of crystal and magnetic properties of the RFeO3 family members. The peculiarities of their complex magnetic structures and their evolution under external conditions, such as temperature, magnetic and electric fields will be studied by polarized neutron diffraction, including both the unique spherical neutron polarimetry technique as well as the classical flipping-ratio method. Investigations of the magnetic dynamics will be performed by means of inelastic neutron scattering, which allows to obtain the magnetic exchange interaction parameters. Detailed studies of RFeO3 crystal structures, namely the search for structural distortions in a weak ferromagnetic phase to demonstrate the expected symmetry lowering will be done by both unpolarized neutron and X-ray diffraction techniques as well as dilatometry measurements. Results of the proposed experimental studies will be analyzed in relation to the ferroelectric phases of these materials. Based on the obtained results, the model of magnetoelectric interactions responsible for the multiferroic properties in orthoferrites will be developed and its level of universality will be established.