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

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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.