arXiv subjects

Hiroki Yamauchi

Publications and source records attributed to Hiroki Yamauchi.

5 recordsLinked to original sources

arXiv2023

Nature of the Antiferromagnetic Order in GdCu$_2$

A magnetic order in orthorhombic GdCu$_2$ was investigated via a single crystal neutron diffraction with thermal neutron. Magnetic peaks were observed at incommensurate positions described by the ordering vector $q$=($δ$,~1,~0) with $δ$=0.678 at 4.6~K. This ordering vector is close to the commensurate one with $q_{\rm c}$=(2/3,~1,~0) reported earlier, but clearly deviates. The incommensurate nature of the magnetic order in GdCu$_2$ is further corroborated by the peak shift with temperature below $T_{\rm N}$.

cond-mat.str-el↗

arXiv2022

Precision beam telescope based on SOI pixel sensor technology for electrons in the energy range of sub-GeV to GeV

We developed a beam telescope system comprising five layers of 300-$μ$m-thick INTPIX4NA monolithic pixel sensors with each pixel size of 17 $μ$m square. The sensors were fabricated using silicon-on-insulator (SOI) technology. The signal-to-noise ratio of 140--230 is realized at a bias voltage of 20~V. The tracker system was tested using a positron beam of 200--822 MeV/c, and various tracking methods are examined to optimize spatial precision achievable at these energies. The best tracking precision including the precision of the sensor under test itself is 11.04 $\pm$ 0.10 $μ$m for 822-MeV/c positrons for an equidistant sensor spacing of 32 mm. The achieved precision results combined with the intrinsic spatial resolution value obtained for a similar system using 120 GeV protons are used to estimate the tracking performance of electrons in the GeV energy range; a tracking precision of 2.22 $μ$m is evaluated for 5-GeV electrons. The method to estimate the tracking performance is verified using a Geant4-based simulation. The developed high precision tracker system enables to map the detailed performance of the sensors with pixel sizes of $\mathcal{O}$(10 $μ$m), therefore will be a powerful system for development of devices targeting precision position resolutions.

physics.ins-det↗

arXiv2018

Neutron-scattering study of yttrium iron garnet

The nuclear and magnetic structure and full magnon dispersions of yttrium iron garnet Y$_3$Fe$_5$O$_{12}$ have been studied by neutron scattering. The refined nuclear structure is distorted to a trigonal space group of $R\bar{3}$. The highest-energy dispersion extends up to 86 meV. The observed dispersions are reproduced by a simple model with three nearest-neighbor-exchange integrals between 16$a$ (octahedral) and 24$d$ (tetrahedral) sites, $J_{aa}$, $J_{ad}$, and $J_{dd}$, which are estimated to be 0.00$\pm$0.05, $-$2.90$\pm$0.07, and $-$0.35$\pm$0.08 meV, respectively. The lowest-energy dispersion below 14 meV exhibits a quadratic dispersion as expected from ferromagnetic magnons. The imaginary part of $q$-integrated dynamical spin susceptibility $χ$"($E$) exhibits a square-root energy-dependence in the low energies. The magnon density of state is estimated from the $χ$"($E$) obtained on an absolute scale. The value is consistent with a single polarization mode for the magnon branch expected theoretically.

cond-mat.mtrl-sci↗

arXiv2011

Magnons and electromagnons in a spin-lattice-coupled frustrated magnet CuFeO2 as seen via inelastic neutron scattering

We have investigated spin-wave excitations in a four-sublattice (4SL) magnetic ground state of a frustrated magnet CuFeO2, in which `electromagnon' (electric-field-active magnon) excitation has been discovered by recent terahertz time-domain spectroscopy [Seki et al. Phys. Rev. Lett. 105 097207 (2010)]. In previous study, we have identified two spin-wave branches in the 4SL phase by means of inelastic neutron scattering measurements under applied uniaxial pressure. [T. Nakajima et al. J. Phys. Soc. Jpn. 80 014714 (2011) ] In the present study, we have performed high-energy-resolution inelastic neutron scattering measurements in the 4SL phase, resolving fine structures of the lower-energy spin-wave branch near the zone center. Taking account of the spin-driven lattice distortions in the 4SL phase, we have developed a model Hamiltonian to describe the spin-wave excitations. The determined Hamiltonian parameters have successfully reproduced the spin-wave dispersion relations and intensity maps obtained in the inelastic neutron scattering measurements. The results of the spin-wave analysis have also revealed physical pictures of the magnon and electromagnon modes in the 4SL phase, suggesting that collinear and noncollinear characters of the two spin-wave modes are the keys to understand the dynamical coupling between the spins and electric dipole moments in this system.

cond-mat.str-el↗

arXiv2002

Magnetic Phase Diagrams with Possible Field-induced Antiferroquadrupolar Order in TbB$_2$C$_2$

Magnetic phase diagrams of a tetragonal antiferromagnet TbB$_2$C$_2$ were clarified by temperature and field dependence of magnetization. It is noticeable that the N{é}el temperature in TbB$_2$C$_2$ is anomalously enhanced with magnetic fields, in particular the enhancement reaches 13.5 K for the ${<}1 1 0{>}$ direction at 10 T. The magnetization processes as well as the phase diagrams are well interpreted assuming that there appear field-induced antiferroquadrupolar ordered phases in TbB$_2$C$_2$. The phase diagrams of the AFQ compounds in RB$_2$C$_2$ are systematically understood in terms of the competition with AFQ and AFM interactions.

cond-mat.str-el↗