arXiv subjects

Mitsuru Tsukagoshi

Publications and source records attributed to Mitsuru Tsukagoshi.

8 recordsLinked to original sources

arXiv2026

Conical Magnetic Structure and Atomic Displacements in Chiral Helimagnet Yb(Ni,Cu)$_3$Al$_9$ in Magnetic Fields along the Helical $c$ Axis

We investigated the conical magnetic state of a uniaxial chiral helimagnet Yb(Ni$_{1-x}$Cu$_x$)$_3$Al$_9$ induced in magnetic fields applied along the $c$ axis, which coincides with the helical axis at zero field. Using resonant X-ray diffraction, we clearly observed the disappearance of magnetic satellite peaks, corresponding to the transition from the conical to the field-induced ferromagnetic state. The critical fields were determined to be 4 T for $x=0$ and 7 T for $x= 0.05$, which were hardly discernible in the magnetization curves. We also found that atomic displacements with the same propagation vector emerge simultaneously with the onset of the conical order. The transition temperature $T_{\text{N}}$ and the critical fields for $H \parallel c$ ($H_{\text{c}}^{z}$) and $H\perp c$ ($H_{\text{c}}^{x}$) are discussed on the basis of a mean-field calculation for a simple $q=1$ model of the magnetic structure. We propose that $T_{\text{N}}$ and $H_{\text{c}}^{z}$ primarily reflect the dominant intralayer exchange interactions within the honeycomb Yb-layer, whereas $H_{\text{c}}^{x}$ is governed by the much weaker interlayer coupling.

cond-mat.str-el↗

arXiv2023

Discovery of antiferromagnetic chiral helical ordered state in trigonal GdNi$_3$Ga$_9$

We have performed magnetic susceptibility, magnetization, and specific heat measurements on a chiral magnet GdNi$_3$Ga$_9$, belonging to the trigonal space group $R32$ (\#155). A magnetic phase transition takes place at $T_{\rm N}$ = 19.5 K. By applying a magnetic field along the $a$ axis at 2 K, the magnetization curve exhibits two jumps at $\sim$ 3 kOe and = 45 kOe. To determine the magnetic structure, we performed a resonant X-ray diffraction experiment by utilizing a circularly polarized beam. It is shown that a long-period antiferromagnetic (AFM) helical order is realized at zero field. The Gd spins in the honeycomb layer are coupled in an antiferromagnetic manner in the $c$ plane and rotate with a propagation vector $q$ = (0, 0, 1.485). The period of the helix is 66.7 unit cells ($\sim 180$~nm). In magnetic fields above 3~kOe applied perpendicular to the helical $c$ axis, the AFM helical order changes to an AFM order with $q$ = (0, 0, 1.5).

cond-mat.str-el↗

arXiv2023

Distorted triangular skyrmion lattice in a noncentrosymmetric tetragonal magnet

Magnetic skyrmions are particle-like spin-swirling objects ubiquitously realized in magnets. They are topologically stable chiral kinks composed of multiple modulation waves of spiral spin structures, where the helicity of each spiral is usually selected by antisymmetric exchange interactions in noncentrosymmetric crystals. We report an experimental observation of a distorted triangular lattice of skyrmions in the polar tetragonal magnet EuNiGe$_3$, reflecting a strong coupling with the lattice. Moreover, through resonant x-ray diffraction, we find that the magnetic helicity of the original spiral at zero field is reversed when the skyrmion lattice is formed in a magnetic field. This means that the energy gain provided by the skyrmion lattice formation is larger than the antisymmetric exchange interaction. Our findings will lead us to a further understanding of emergent magnetic states.

cond-mat.str-el↗

arXiv2023

Helicity Selection of the Cycloidal Order in Noncentrosymmetric EuIrGe$_3$

The magnetic helicities of the cycloidal ordering in EuIrGe$_3$, with a noncentrosymmetric tetragonal structure, have been studied by circularly polarized resonant X-ray diffraction. It is shown that the helicity of each cycloidal domain is uniquely determined and satisfies the symmetry relations of the $C_{4v}$ point group of the crystal structure. The result shows that the cycloidal helicity is determined by the Dzyaloshinskii-Moriya type antisymmetric exchange interaction. The domain selection and the phase transition by the external magnetic field along [100] and [110] have also been studied. It is shown that the cycloidal plane prefers to be perpendicular to the field and the transverse conical state is realized.

cond-mat.str-el↗

arXiv2023

Crystal field excitation in the chiral helimagnet YbNi$_3$Al$_9$

Crystal field level scheme of a uniaxial chiral helimagnet YbNi$_3$Al$_9$, exhibiting a chiral magnetic soliton lattice state by Cu substitution for Ni, has been determined by inelastic neutron scattering. The ground and the first excited doublets are separated by 44 K and are simply expressed as $α|\pm 7/2\rangle + β|\mp 5/2\rangle$ with $α$ and $β$ nearly equal to $\pm 1/\sqrt{2}$. The easy axis of the crystal field anisotropy is the $c$ axis when the excited levels are populated at high temperatures and high magnetic fields. On the other hand, the magnetism at low temperatures and low magnetic fields, where only the ground doublet is populated, is described by an easy plane anisotropy which may be treated as an $S=1/2$ system with an anisotropic $g$-factor, $g_{xy}=3.02$ and $g_z=1.14$. An orbital dependent exchange interaction is also discussed to explain the temperature dependence of the magnetic susceptibility based on this level scheme.

cond-mat.str-el↗

arXiv2022

Cycloidal Magnetic Ordering in Noncentrosymmetric EuIrGe$_3$

Successive magnetic phase transitions at $T_{\text{N}}$=12.2 K, $T_{\text{N}}^{\;\prime}$=7.0 K, and $T_{\text{N}}^{\;*}$=5.0 K in EuIrGe$_3$, an intermetallic compound with a body centered tetragonal lattice belonging to a polar space group $I4mm$, has been investigated by neutron diffraction and resonant X-ray diffraction. It is shown that EuIrGe$_3$ exhibits an incommensurate longitudinal sinusoidal order with $q\sim (0, 0, 0.792)$ and $m_{q} \parallel c\text{-axis}$ in the high temperature phase ($T_{\text{N}}^{\;\prime}< T < T_{\text{N}}$), which changes to a cycloidal order with $q=(δ', 0, 0.8)$ ($δ'\sim 0.017$) and $m_{q} \parallel ac\text{-plane}$ in the intermediate phase ($T_{\text{N}}^{\;*} < T < T_{\text{N}}^{\;\prime}$). In the low temperature phase ($T < T_{\text{N}}^{\;*}$), the cycloidal plane rotates by $45^{\circ}$ to have $q=(δ, δ, 0.8)$ ($δ\sim 0.012$). It is also pointed out that the X-ray scattering amplitude from odd-parity magnetic quadrupole due to the polar environment interfere with that from normal even-parity magnetic dipole in the magnetic ordered phase.

cond-mat.str-el↗

arXiv2022

Structural Transition in the Hidden Ordered Phase of CeCoSi

We have performed X-ray diffraction experiments on a single crystalline CeCoSi to investigate the unresolved ordered phase below $T_0 \sim 12$ K. We have discovered that a triclinic lattice distortion takes place below $T_0$, which is further modified in the subsequent antiferromagnetic ordered phase. The structural domains can be selected by applying a magnetic field, indicating that some electronic ordering exists behind and affects the magnetic anisotropy in the hidden ordered phase below $T_0$. The transition at $T_0$, although the order parameter is still unknown, is associated with the maximum in the $c$-axis lattice parameter. In magnetic fields along $[1, 0, 0]$, the structural transition temperature, named as $T_{\text{s1}}$, deviates from $T_0$ and decreases with increasing the field, whereas $T_0$ increases. This shows that the hidden ordered phase without triclinic distortion exists between $T_{\text{s1}}$ and $T_0$. The results for $H \parallel [1, 1, 0]$ are also reported.

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arXiv2022

Competition between helimagnetic and ferroquadrupolar orderings in a monoaxial chiral magnet DyNi$_3$Ga$_{9}$ studied by resonant x-ray diffraction

Successive phase transitions in a rare-earth monoaxial chiral magnet DyNi$_3$Ga$_{9}$ have been investigated by resonant x-ray diffraction. Magnetic dipole and electric quadrupole degrees of freedom arising from the large angular moment of $J=15/2$, in combination with the symmetric and antisymmetric exchange interactions and the crystal field anisotropy, give rise to competing ordered phases. We show that the antiferromagnetically coupled Dy moments in the $ab$-plane form an incommensurate helimagnetic order with $q\sim(0, 0, 0.43)$ just below $T_{\text{N}}=10$ K, which further exhibits successive first-order transitions to the commensurate helimagnetic order with $q=(0,0,0.5)$ at $T_{\text{N}}^{\;\prime}=9.0$ K, and to the canted antiferromagnetic order with $q=(0,0,0)$ at $T_{\text{N}}^{\;\prime\prime}=8.5$ K, both with large coexistence regions. The relation of the magnetic helicity and the crystal chirality in DyNi$_3$Ga$_{9}$ is also uniquely determined. Splitting of the $(6,0,0)$ Bragg peak is observed below $T_{\text{N}}^{\;\prime\prime}$, reflecting the lattice distortion due to the ferroquadrupole order. In the canted antiferromagnetic phase, a spin-flop transition takes place at 5 K when the temperature is swept in a weak magnetic field. We discuss these transitions from the viewpoint of competing energies described above.

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