Naoya Kanazawa

We have observed an unconventional, likely topological, Hall effect over a wide temperature region in the magnetization process of a chiral-lattice helimagnet MnGe. The magnitude of the topological Hall resistivity is nearly temperature-independent below 70 K, which reflects the real-space fictitious magnetic field proportional to a geometric quantity (scalar spin chirality) of the underlying spin texture. From the neutron diffraction study, it is anticipated that a relatively short-period (3-6

We have investigated the magnetic structure in a polycrystalline sample of the $B20$-type MnGe by means of small-angle neutron scattering. On the projected diffraction plane normal to the incoming neutron beam, a Debye-ring-like pattern appears due to the random orientation of the spin helix $q$ vectors ($\ensuremath{\parallel}\ensuremath{\langle}100\ensuremath{\rangle}$). When an external magnetic field is applied normal to the incoming neutron beam, an intense peak with wave vector ($q$) perpe

Second-order continuous phase transitions are characterized by symmetry breaking with order parameters. Topological orders of electrons, characterized by the topological index defined in momentum space, provide a distinct perspective for phase transitions, which are categorized as quantum phase transitions not being accompanied by symmetry breaking. However, there are still limited observations of counterparts in real space. Here we show a real-space topological phase transition in a chiral magn

We investigate the skyrmion formation process in nanostructured FeGe Hall-bar devices by measurements of the topological Hall effect, which extracts the winding number of a spin texture as an emergent magnetic field. Stepwise profiles of the topological Hall resistivity are observed in the course of varying the applied magnetic field, which arise from instantaneous changes in the magnetic nanostructure such as the creation, annihilation, and jittering motion of skyrmions. The discrete changes in

In the three-dimensional (3D) Heisenberg model, topological point defects known as spin hedgehogs behave as emergent magnetic monopoles, i.e., quantized sources and sinks of gauge fields that couple strongly to conduction electrons, and cause unconventional transport responses such as the gigantic Hall effect. We observe a dramatic change in the Hall effect upon the transformation of a spin hedgehog crystal in a chiral magnet MnGe through combined measurements of magnetotransport and small-angle

We report the engineering of spin-hedgehog crystals in thin films of the chiral magnet MnGe by tailoring the magnetic anisotropy. As evidenced by neutron scattering on films with different thicknesses and by varying a magnetic field, we can realize continuously deformable spin-hedgehog crystals, each of which is described as a superposition state of a different set of three spin spirals (a triple-$\mathbit{q}$ state). The directions of the three propagation vectors $\mathbit{q}$ vary systematica

Spiral spin orders often produce various fascinating phenomena via interaction with electronic structures. Examples include, but are not limited to, multiferroicity and skyrmion formation. Among them, a deformed spiral spin structure, which can be viewed as a periodic sequence of 2$\ensuremath{\pi}$ spin-rotation kinks, can exhibit the functionality of information transmission owing to its phase coherence. This is the chiral magnetic soliton lattice (CSL). Here, the authors have succeeded in bui

FeSi is a nonmagnetic narrow-gap insulator, exhibiting peculiar charge and spin dynamics beyond a simple band structure picture. Those unusual features have been attracting renewed attention from topological aspects. Although the surface conduction was demonstrated according to size-dependent resistivity in bulk crystals, its topological characteristics and consequent electromagnetic responses remain elusive. Here, we demonstrate an inherent surface ferromagnetic-metal state of FeSi thin films a