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Nakajima Group

Associate Professor NAKAJIMA, Taro
Research Associate SAITO, Hiraku

Research Subjects

  • Neutron scattering studies on topological magnetic orders and their dynamics
  • Magnetic structure analysis by means of polarized neutron scattering
  • Control of magnetic and dielectric properties in multiferroics by means of anisotropic stress
  • Time-resolved neutron scattering studies on nonequilibrium and transient phenomena

Magnetism in solids has been extensively studied in the field of condensed matter physics. A well-known example is ferromagnetism, which means that magnetic moments in a solid are spontaneously aligned to be parallel to each other owing to exchange interactions. Besides the ferromagnetism, there are various types of orders of magnetic moments, such as collinear antiferromagnetic and helical magnetic orders. Among them, non-collinear or non-coplanar magnetic orders have recently attracted increasing attention because they can lead to time-space symmetry breaking which may dramatically alter electronic properties of the systems. We study emergent phenomena induced by the non-collinear/non-coplanar spin orders by means of neutron and X-ray scattering techniques. One example is spin-driven ferroelectricity, where a spiral magnetic order breaks spatial inversion symmetry of the system and leads to spontaneous electric polarization. Another example is a vortex-like spin texture called magnetic skyrmiom, which often appears in a long-wavelength helimagnet. By the virtue of the topologically-nontrivial spin texture, the magnetic skyrmion induces an effective magnetic field acting only on conduction electrons. We are also exploring new methodologies in neutron and X-ray scatterings, such as time-resolved neutron scattering, to investigate the unconventional magnetic orders in detail.

(a) A schematic of magnetic skyrmion lattice. (b) The equilibrium and metastable state diagram of MnSi. The metastable skyrmion lattice state is realized by a rapid temperature sweep in a magnetic field of 0.2 T.
The results of time-resolved neutron scattering measurement on MnSi in a magnetic field; the hexagonal diffraction patterns correspond to a triangular lattice of metastable skyrmions.

Publications and Research Highlights