第6回物理工学科教室談話会[Prof. Dmytro Inosov・10/7(月)15:00～16:30]
講 師：Prof. Dmytro Inosov
所 属：Technische Universität Dresden（ドレスデン工科大学）
題 目：Specifics of spin excitations in centrosymmetric helimagnets
日 時：2024 年 10 月 7 日(月)15:00～16:30
Date and Time: October 7, 2024 (Monday) 15:00-16:30
場 所：工 6 号館 1 階大会議室
Place: Large Conference room, 1st floor, Engineering Bldg. 6
Abstract:
Noncollinear long-range ordered magnetic structures that break chiral symmetry can arise either as a result of Dzyaloshinskii-Moriya interactions in lattices with broken inversion symmetry or as a result of bond frustration in structurally centrosymmetric crystals. While in the former case the spin chirality is uniquely chosen by the lattice symmetry, in the latter case the chiral symmetry is broken spontaneously, so that both right- and left-handed magnetic domains can coexist. Using inelastic neutron scattering, we have studied spin waves in a number of centrosymmetric helimagnets with different magnetic ground states. The cubic spinel ZnCr2Se4 is described by frustrated interactions and represents a perfect model system for studying the Heisenberg model on the perfect pyrochlore lattice. Here, an emergent energy scale of the pseudo-Goldstone magnon gap leads to highly nontrivial thermodynamic and thermal transport properties and to the appearance of a field-induced spiral spin liquid state. The iron perovskite compounds SrFeO3 and Sr3Fe2O7, on the other hand, avoid the simple spin-spiral state and form multiple-q orders of various types, whose spin-wave spectrum is still a challenge for theoretical calculations. At elevated temperatures, all the mentioned compounds exhibit an intense quasielastic spin-fluctuation spectrum in neutron spectroscopy, which coexists with the sharp collective spin-wave excitations and could be a universal feature of the centrosymmetric helimagnets in general. It is possible that its origin is connected with the dynamics of domain walls that separate helimagnetic domains of opposite chirality.
紹介教員：：求幸年教授（物理工学専攻）、中島多朗准教授（物性研究所）