arXiv subjects

Takuro Kawasaki

Publications and source records attributed to Takuro Kawasaki.

4 recordsLinked to original sources

arXiv2026

Polarized neutron diffraction with ex-situ $^3$He neutron spin filter and two-dimensional detector for noncollinear incommensurate magnetic order

Polarized neutron scattering has been widely used for studying magnetic orders in condensed matter. A typical setup for this technique is a triple-axis spectrometer with a ferromagnetic single-crystal monochromator and analyzer, which is suited for point-by-point measurements within the horizontal scattering plane. However, this setup cannot fully meet the demands of recent studies on complex magnetic orders with emergent cross-correlated phenomena. For instance, multiferroics, magnetic skyrmions, and other topologically nontrivial magnetic orders tend to have incommensurate magnetic modulation vectors running along various directions in reciprocal space, which cannot be captured by measurements restricted to the horizontal scattering plane. To overcome these limitations, we have developed an experimental setup combining a $^3$He neutron spin filter ($^3$He-NSF) and a two-dimensional (2D) detector, which enables us to analyze the polarization of neutrons scattered away from the horizontal plane. We also establish a data reduction procedure to convert the 2D intensity maps into three-dimensional intensity distributions in reciprocal space, correcting for the effect of imperfect $^3$He polarization. This method is applied to single-crystal diffraction measurements on the multiferroic material Mn$_3$WO$_6$, which exhibits complex incommensurate magnetic orders. We have successfully observed polarization-dependent intensities of out-of-plane incommensurate magnetic reflections, demonstrating the effectiveness of the present method for analyzing complex magnetic structures.

cond-mat.str-el↗

arXiv2026

Uniaxial stress effects on magnetic and electric properties of the ground state in a centrosymmetric magnetic skyrmion host Gd$_2$PdSi$_3$

We investigate effects of uniaxial stress to magnetic orders and electrical resistivity of the centrosymmetric magnetic skyrmion compound Gd$_2$PdSi$_3$, which has a hexagonal crystal structure composed of triangular lattice layers of magnetic Gd$^{3+}$ ions. This compound is known to exhibit the triple-$q$ magnetic skyrmion lattice phase with a giant topological Hall effect in the first field induced phase [T. Kurumaji $\textit{et al}$. Science $\textbf{365}$, 914-918 (2019)]. In contrast to the established picture of the field-induced phase, the ground state of this system still remains to be studied. Although previous studies reported the existence of the incommensurate magnetic modulations described by a magnetic modulation wave vector ${\bf q}=(q,0,0)$ where $q\sim 0.14$ and its equivalents, it is still unclear whether the magnetic structure is a single-$q$ structure or a multiple-$q$ structure. In the present study, we performed magnetization, resistivity and neutron diffraction measurements with a compressive uniaxial stress applied perpendicular to the $c$ axis. The observed data revealed that the system did not exhibit anisotropic magnetic and electric properties expected from a single-$q$ magnetic order, suggesting that the magnetic ground state of this system is a multi-$q$ magnetic order.

cond-mat.str-el↗

arXiv2021

Charge-Density-Wave Order and Multiple Magnetic Transitions in Divalent Europium Compound EuAl$_4$

Multiple transition phenomena in divalent Eu compound EuAl$_4$ with the tetragonal structure were investigated via the single-crystal time-of-flight neutron Laue technique. At 30.0 K below a charge-density-wave (CDW) transition temperature of $T_{\rm CDW}$ = 140 K, superlattice peaks emerge near nuclear Bragg peaks described by an ordering vector $q_{\rm CDW}$=(0 0 $δ_c$) with $δ_c{\sim}$0.19. In contrast, magnetic peaks appear at $q_2 = (δ_2 δ_2 0)$ with $δ_2$ = 0.085 in a magnetic-ordered phase at 13.5 K below $T_{\rm N1}$ = 15.4 K. By further cooling to below $T_{\rm N3}$ = 12.2 K, the magnetic ordering vector changes into $q_1 = (δ_1 0 0)$ with $δ_1$ = 0.17 at 11.5 K and slightly shifts to $δ_1$ = 0.194 at 4.3 K. No distinct change in the magnetic Bragg peak was detected at $T_{\rm N2}$=13.2 K and $T_{\rm N4}$=10.0 K. The structural modulation below $T_{\rm CDW}$ with $q_{\rm CDW}$ is characterized by the absence of the superlattice peak in the (0 0 $l$) axis. As a similar CDW transition was observed in SrAl$_4$, the structural modulation with $q_{\rm CDW}$ could be mainly ascribed to the displacement of Al ions within the tetragonal $ab$-plane. Complex magnetic transitions are in stark contrast to a simple collinear magnetic structure in isovalent EuGa$_4$. This could stem from different electronic structures with the CDW transition between two compounds.

cond-mat.str-el↗

arXiv2016

Magnetic structure of divalent europium compound EuGa$_4$ studied by single crystal time-of-flight neutron diffraction

The magnetic structure of the intermetallic compound EuGa$_4$ was investigated using single-crystal neutron diffraction with the time-of-flight (TOF) Laue technique on the new diffractometer SENJU at MLF of J-PARC. In spite of high neutron absorption of Eu, a vast number of diffraction spots were observed without isotope enrichment. The magnetic reflections were appeared at the positions with the diffraction indices of $h+k+l{\neq}2n$ below 16 K, indicating that the ordering vector is ${\bf q}=(0~0~0)$. Continuous evolution of magnetic reflection intensity below $T_{\rm N}$ follows a squared Brillouin function for $S$=7/2. By adopting a wavelength-dependent absorption collection, the magnetic structure of EuGa$_4$ was revealed that a nearly full magnetic moment of 6.4$~μ_{\rm B}$ of Eu lies within the basal plane of the lattice. The present study reveals a well-localized divalent Eu magnetism in EuGa$_4$ and demonstrates a high ability of SENJU to investigate materials with high neutron absorption.

cond-mat.str-el↗