R. Takagi 교수

Magnetic skyrmions are topologically stable swirling spin textures with particle-like character, and have been intensively studied as a candidate of high-density information bit. While magnetic skyrmions were originally discovered in noncentrosymmetric systems with Dzyaloshinskii-Moriya interaction, recently a nanometric skyrmion lattice has also been reported for centrosymmetric rare-earth compounds, such as Gd₂PdSi₃ and GdRu₂Si₂. For the latter syste

Propagation character of spin wave was investigated for chiral magnets FeGe and Co-Zn-Mn alloys, which can host magnetic skyrmions near room temperature. On the basis of the frequency shift between counterpropagating spin waves, the magnitude and sign of Dzyaloshinskii-Moriya (DM) interaction were directly evaluated. The obtained magnetic parameters quantitatively account for the size and helicity of skyrmions as well as their materials variation, proving that the DM interaction plays a decisive

Magnetic skyrmion is a topologically protected particle-like object in magnetic materials, appearing as a nanometric swirling spin texture. The size and shape of skyrmion particles can be flexibly controlled by external stimuli, which suggests unique features of their crystallization and lattice transformation process. Here, we investigated the detailed mechanism of structural transition of skyrmion lattice (SkL) in a prototype chiral cubic magnet Cu₂OSeO₃, by combining res

The real-space spin texture and the relevant magnetic parameters were investigated for an easy-axis noncentrosymmetric ferromagnet Cr_{11}Ge_{19} with Nowotny chimney ladder structure. Using Lorentz transmission electron microscopy, we report the formation of bi-Skyrmions, i.e., pairs of spin vortices with opposite magnetic helicities. The quantitative evaluation of the magnetocrystalline anisotropy and Dzyaloshinskii-Moriya interaction (DMI) proves that the magnetic dipolar interaction plays a

Magnetic skyrmions have attracted attention as particlelike swirling spin textures with nontrivial topology, and their self-assembled periodic order i.e., the skyrmion crystal (SkX) is anticipated to host unique magnonic properties. In this paper, we investigate magnetic resonance in the quenched SkX state, which is obtained by the rapid cooling of the high-temperature equilibrium SkX phase in the chiral magnetic insulator ${\mathrm{Cu}}_{2}\mathrm{O}\mathrm{Se}{\mathrm{O}}_{3}$. At low temperat

We report the experimental observation of longitudinal spin Seebeck effect in a multiferroic helimagnet Ba0.5Sr1.5Zn2Fe12O22. Temperature gradient applied normal to Ba0.5Sr1.5Zn2Fe12O22/Pt interface generates inverse spin Hall voltage of spin current origin in Pt, whose magnitude was found to be proportional to bulk magnetization of Ba0.5Sr1.5Zn2Fe12O22 even through the successive magnetic transitions among various helimagnetic and ferrimagnetic phases. This finding demonstrates that the helimag

The molecular conductors $[{M(\text{tmdt})}_{2}]$ ($M=\text{Ni}$, Pt) consisting of single molecular species are investigated with $^{13}\mathrm{C}$ NMR and $^{1}\mathrm{H}$ NMR. The temperature dependences of the $^{13}\mathrm{C}$ NMR shift and relaxation rate provide microscopic evidence for the metallic nature with appreciable electron correlations. Both compounds exhibit an anomalous frequency-dependent enhancement in the $^{1}\mathrm{H}$ nuclear spin-lattice relaxation rate in a wide temper

Internal cation mobilities of Li+ and K+ in the system were determined experimentally using the counter current electromigration method over the temperature range 700–778 K, with initial equivalent fractions of of 0.356, 0.416, and 0.451. The relative difference in internal cation mobilities of Li+ and K+ was found to reach as much as 7% in this range.

The magnetic state of the single-component molecular compound [Cu(tmdt)${}_{2}$], where tmdt indicates tetramethylene tetrathiafulvalene dithiolate, is investigated by means of ${}^{1}$H NMR. An abrupt spectral broadening below 13 K and a sharp peak in the nuclear spin-lattice relaxation rate ${T}_{1}^{\ensuremath{-}1}$ at 13 K are observed as clear manifestations of a second-order antiferromagnetic transition, which is consistent with the previously reported magnetic susceptibility and electron

$^{13}\mathrm{C}$ nuclear magnetic resonance measurements were performed for a single-component molecular material Zn(tmdt)${}_{2}$, in which tmdt's form an arrangement similar to the so-called $\ensuremath{\kappa}$-type molecular packing in quasi-two-dimensional Mott insulators and superconductors. A detailed analysis of the powder spectra uncovered local spin susceptibility in the tmdt $\ensuremath{\pi}$ orbitals. The obtained shift and relaxation rate revealed singlet-triplet excitations of t

We investigated a system based solely on a single molecular species, $\text{Cu}({\mathrm{tmdt})}_{2}$, accommodating $d$ and $\ensuremath{\pi}$ orbitals within the molecule. $^{13}\mathrm{C}$ nuclear magnetic resonance measurements captured singlet-triplet excitations of $\ensuremath{\pi}$ spins indicating the existence of a $\ensuremath{\pi}$-electron-based spin-gapped Mott insulating subsystem, which has been hidden by the large magnetic susceptibility exhibited by the $d$ spins forming antife

A family of compounds built by a single molecular species, $M$(${\mathrm{tmdt})}_{2}$, with a metal ion, $M$, and organic ligands, tmdt, affords diverse electronic phases due to $M$-dependent interplays between $d$ electrons in $M$, and $\ensuremath{\pi}$ electrons in tmdt. We investigated the spin state in $\mathrm{Pd}{(\mathrm{tmdt})}_{2}$, a $\ensuremath{\pi}$-electron system without a $d$-electron contribution, through $^{1}\mathrm{H}$ nuclear magnetic resonance (NMR) and muon-spin resonance

The authors examine the spin and charge states in a multiorbital system through orbital selective NMR spectroscopy combined with fine-structure-resolvable synchrotron X-ray diffractometry. The results show an intramolecular electron redistribution leading to interorbital self-doping