Hideya Onodera

Bio: Hideya Onodera is an academic researcher from Tohoku University. The author has contributed to research in topics: Magnetization & Magnetic structure. The author has an hindex of 28, co-authored 142 publications receiving 2148 citations.

Antiferroquadrupolar ordering and magnetic properties of the tetragonal DyB2C2 compound

Abstract: Magnetic properties were investigated on a single-crystalline DyB 2 C 2 compound with the tetragonal structure. Spontaneous magnetizations appear along the a- and [1 1 0]-directions below T C =15.3 K. A very small shoulder is observed only along the c -axis at T Q =24.7 K, although large λ-type anomalous specific heats are observed at T C and T Q . There exists a large magnetic anisotropy in the tetragonal basal plane which is observed in magnetization processes below T C . Neutron powder diffraction experiments reveal that magnetic reflections are observed only below T C . In the magnetically ordered phase, the Dy moments are arranged to be perpendicular to neighbors along the c -axis. The results are well interpreted by postulating that the phase between T C and T Q is an antiferroquadrupolar ordered one. DyB 2 C 2 is a novel compound with a high antiferroquadrupolar ordering temperature of 24.7 K.

Magnetization and coercivity of Mn3−δGa alloys with a D022‐type structure

Abstract: The D022‐type (Al3Ti‐type) phase in the Mn–Ga system is ferrimagnetic; the spin direction is parallel to the tetragonal c axis The Curie temperature is about 765 K (for δ=067), near the decomposition temperature We have prepared the D022‐type alloys by annealing the quenched ingots of the high‐temperature phase (γMn phase) at 400 or 300 °C for a long time The preparation becomes much easier if the ingots are powdered by filing before the annealing The single‐phase specimens of Mn3−δGa were obtained in the composition range 015≤δ≤106 The coercivity of some specimens was so large that we measured the magnetization curve in high magnetic fields up to 150 kOe The room‐temperature values of saturation magnetization, remanent magnetization, and coercivity of the powder sample of the alloy with δ=067 are 50 emu/g, 25 emu/g, and 135 kOe, respectively We have also studied the effect of magnetic annealing during the transition from the γMn phase to the D022‐type phase and the effect of the addition of Fe to Mn3−δGa of the D022‐type phase

Quadrupolar ordering and magnetic properties of tetragonal TmAu 2

Abstract: Magnetic susceptibility, magnetization process, specific heat, ultrasonic velocity, and inelastic neutron scattering experiments were performed on powdered and single-crystalline ${\mathrm{TmAu}}_{2}$ samples. ${\mathrm{TmAu}}_{2}$ with a simple body-centered tetragonal ${\mathrm{MoSi}}_{2}$-type structure undergoes a transition to an antiferromagnetic state at ${T}_{N}$ of 3.2 K. An anomaly at 7.0 K is observed in the temperature dependence of specific heat and magnetic susceptibility. A very large softening beyond 50% from 300 down to 7.0 K is also observed in the temperature dependence of the elastic constant of the ${C}_{11}\ensuremath{-}{C}_{12}$ mode. The results reveal clearly that the anomaly at 7.0 K ${(=T}_{Q})$ originates from a ferroquadrupolar ordering with an orthorhombic $\ensuremath{\gamma}$-symmetry-lowering mode. Separation between the ground and the first excited singlet states of $4f$ levels is so small in the quadrupolar ordered phase and a transition probability between these states is so extremely large that there occurs a Van Vleck antiferromagnetic transition at 3.2 K by exchange-induced magnetic moments arising from the transition between the ground and the first excited singlet states.

Anomalous Magnetic Phase Diagrams of HoB2C2. Antiferroquadrupolar Ordering in the Magnetic Phase.

Abstract: Magnetic properties of the single-crystalline tetragonal HoB 2 C 2 compound were investigated. An antiferromagnetic transition occurs at 5.8 K. At 5.0 K, a spin-reorientation transition of the first order occurs, and spontaneous magnetizations appear along the a - and [1 1 0]-axes. Magnetization processes below 5.0 K are well scaled down from those of the antiferroquadrupolar ordering compound DyB 2 C 2 and are well interpreted by postulating the magnetic structure similar to that of DyB 2 C 2 . The phase below 5.0 K is the one with competitive coexistence of the antiferromagnetic and antiferroquadrupolar order. The result implies that the antiferroquadrupolar ordering transition occurs below the antiferromagnetic transition temperature and that a pure antiferroquadrupolar ordered phase only in the magnetic fields exists along the [1 1 0]-axis.

Neutron powder diffraction on Ce11B2C2 and Nd11B2C2 : A new model for the tetragonal crystal structure

Abstract: Crystal structures of CeB 2 C 2 and NdB 2 C 2 were investigated by means of neutron powder diffraction using 11 B enriched samples. Diffraction patterns of Ce 11 B 2 C 2 and Nd 11 B 2 C 2 are very ...

Out-of-Plane Reflection and Refraction of Light by Anisotropic Optical Antenna Metasurfaces with Phase Discontinuities

Abstract: Experiments on ultrathin anisotropic arrays of subwavelength optical antennas display out-of-plane refraction. A powerful three-dimensional (3D) extension of the recently demonstrated generalized laws of refraction and reflection shows that the interface imparts a tangential wavevector to the incident light leading to anomalous beams, which in general are noncoplanar with the incident beam. The refracted beam direction can be controlled by varying the angle between the plane of incidence and the antenna array.

Subwavelength imaging in photonic crystals

Abstract: We investigate the transmission of evanescent waves through a slab of photonic crystal and explore the recently suggested possibility of focusing light with subwavelength resolution. The amplification of near-field waves is shown to rely on resonant coupling mechanisms to surface photon bound states, and the negative refractive index is only one way of realizing this effect. It is found that the periodicity of the photonic crystal imposes an upper cutoff to the transverse wave vector of evanescent waves that can be amplified, and thus a photonic-crystal superlens is free of divergences even in the lossless case. A detailed numerical study of the optical image of such a superlens in two dimensions reveals a subtle and very important interplay between propagating waves and evanescent waves on the final image formation. Particular features that arise due to the presence of near-field light are discussed.