Kazuaki Iwasa - Academia.edu (original) (raw)

Papers by Kazuaki Iwasa

A joint project between KEK and Tohoku University was initiated with the aim of future constructi... more A joint project between KEK and Tohoku University was initiated with the aim of future construction of a polarized neutron spectrometer at the Materials and Life Science Experimental Facility (MLF), J-PARC and research program for functional magnetic materials in 2009. Our principal concept is to achieve higher-energy polarization analysis of inelastic scattering beyond a reactor-based neutron source. We target the energy range up to E = 40 meV with using SEOP for polarizer and bender supermirror as an analyzer of m = 5 to 5.5 as the first step. In the second step, we focus on higher energy experiments (0 meV < E < 100 meV) with a large change of its layout. The basic shield designing has been completed and shielding capability of radiation was assessed. Also, the designs of the beam transport section using m = 4 supermirror guide tubes are completed. In order to achieve a high flux polarized neutron experiment, we plan to adopt cross correlation method. R&D of the correlation...

Advanced Quantum Technologies, 2018

Spin-state transition, also known as spin crossover, plays a key role in diverse systems, includi... more Spin-state transition, also known as spin crossover, plays a key role in diverse systems, including minerals and biological materials. In theory, the boundary range between the low-and high-spin states is expected to enrich the transition and give rise to unusual physical states. However, no compound that realizes a nearly degenerate critical range as the ground state without requiring special external conditions has yet been experimentally identified. This study reports that, by comprehensive measurements of macroscopic physical properties, X-ray diffractometry, and neutron spectroscopy, the Sc substitution in LaCoO 3 destabilizes its nonmagnetic low-spin state and generates an anomalous paramagnetic state accompanied by the enhancement of transport gap and magneto-lattice-expansion as well as the contraction of Co─O distance with the increase of electron site transfer. These phenomena are not well described by the mixture of conventional low-and high-spin states, but by their quantum superposition occurring on the verge of a spin-state transition. The present study enables us to significantly accelerate the design of new advanced materials without requiring special equipment, based on the concept of quantum spin-state criticality. Spin-state transitions appear in a wide range of sciences. [1] For example, they naturally occur under the high pressure of the Earth's inner mantle and are related to seismic-wave responses. [2,3] Spin-crossover complexes exhibit magneto-optical switching functionality. [4] Heme protein activities involve spinstate transitions. [5] The spin-state transition denotes a change between two well-defined spin states, whose boundary ranges

Novel Magnetic Structure of the Low Carrier System CeP and CeAs under External Fields

JJAP series, 1999

Neutron Scattering Studies on 4f2-Electron Multipoles in Pr-based Systems

Journal of the Physical Society of Japan, 2019

The degrees of freedom of electron multipoles in various rare-earth alloy compounds have been inv... more The degrees of freedom of electron multipoles in various rare-earth alloy compounds have been investigated over the last four decades. Recently, it has been found that the multipole orderings accom...

Magnetic-Ordering Propagation Vectors of Terbium Hexaboride Revisited

Journal of the Physical Society of Japan, 2018

The magnetic ordered state of a single-crystal sample of TbB6 has been studied with the high-prec... more The magnetic ordered state of a single-crystal sample of TbB6 has been studied with the high-precision neutron diffraction instrument SENJU installed at BL18 of the Materials and Life Science Facil...

28a-N-9 Devil's Staircase of Magnetic Layered Compound under High pressure

30pXE-3 Natron scattering studies on antiferro-quadrupolar ordering and magnetic excitation of PrFe_4P_

Broad Excitation Spectra between Crystalline-Electric-Field Levels Associated with Non-Kramers Doublet Ground State offElectrons in PrNb2Al20

Journal of the Physical Society of Japan, 2016

Inelastic neutron scattering measurements of PrNb2Al20, which exhibits non-Fermi-liquid behaviors... more Inelastic neutron scattering measurements of PrNb2Al20, which exhibits non-Fermi-liquid behaviors, were carried out in order to determine the f-electron crystalline-electric-field split. Magnetic i...

Journal of the Physical Society of Japan, 2014

Phonons of TbB 6 are studied by inelastic X-ray scattering and compared with those of GdB 6 and D... more Phonons of TbB 6 are studied by inelastic X-ray scattering and compared with those of GdB 6 and DyB 6. Measured low-lying phonon modes located near 6 meV soften distinctly with decreasing temperature, particularly the longitudinal phonon that is dominated by the motion of Tb ions at q 1 ¼ ð1=2; 0; 0Þ. The magnitude and temperature dependence of phonon energy are between those of GdB 6 and DyB 6. We derive a Landau-type free-energy expansion with respect to the atomic displacement in TbB 6 , and discuss a general feature among these three compounds. The systematic variation in the phonon characteristics of these hexaborides and the first-order-like instability indicate the universality of the anharmonic motion of heavy rare-earth atoms in RB 6 (R = Gd, Tb, and Dy).

Journal of Physics: Conference Series, 2012

To investigate the role of multipoles in the phase transitions of NdPd 3 S 4 , measurements of sp... more To investigate the role of multipoles in the phase transitions of NdPd 3 S 4 , measurements of specific heat, magnetization, and electrical resistivity were performed for single-crystalline samples. We also carried out powder neutron diffraction experiments to identify a magnetically ordered structure. At zero magnetic field, an antiferromagnetic (AFM) transition occurs at T N = 1.8 K. When a magnetic field is applied, the AFM ordered phase, characterized by a propagation vector k = (1, 0, 0), switches into field-induced phases. We propose that the field-induced phases are associated with quadrupolar ordering.

$Research paper thumbnail of Successive Phase Transitions in R3Ir4Sn13 (R: La and Ce) Investigated Using Neutron and X-ray Diffraction$

Proceedings of the International Conference on Strongly Correlated Electron Systems (SCES2019), Mar 18, 2020

Successive phase transitions of R 3 Ir 4 Sn 13 (R: La and Ce) were studied using neutron and x-ra... more Successive phase transitions of R 3 Ir 4 Sn 13 (R: La and Ce) were studied using neutron and x-ray diffraction techniques. A semimetal Ce 3 Ir 4 Sn 13 undergoes three phase transitions: an antiferromagnetic ordering characterized by a propagation vector q M = (1/2, 1/2, 2/5) below 0.6 K, a structural transformation with q S2 = (1/4, 1/4, 1/4) at 2.0 K, and another structural transformation with q S1 = (1/2, 1/2, 0) above room temperature. La 3 Ir 4 Sn 13 was confirmed to be a superconductor below 2.5 K under the q S1 = (1/2, 1/2, 0) structure that also appears above room temperature.

$Research paper thumbnail of 6a-PS-61 Low-temperature X-ray diffraction study of RB_6(R=Ce and Gd)$

6a-PS-61 Low-temperature X-ray diffraction study of RB_6(R=Ce and Gd)

Meeting Abstracts of the Physical Society of Japan (Nihon Butsuri Gakkai koen gaiyoshu), 1997

Investigation of 3D Atomic Local Structures around Dopants by Using Neutron Atomic-Resolution Holography

To investigate effects of doping in functional materials, we have developed the unique atomic-res... more To investigate effects of doping in functional materials, we have developed the unique atomic-resolution neutron holography technique that can be used to observe local structures around light-element dopants. Because of the importance of light elements in functional materials, this technique will have a significant influence in the field of materials science.

Magnetic structure and lattice distortion of GdB6 Keitaro KUWAHARA, Ryunosuke YAMAMOTO, Masahumi ... more Magnetic structure and lattice distortion of GdB6 Keitaro KUWAHARA, Ryunosuke YAMAMOTO, Masahumi KOHGI, Hironori NAKAO, Kenji ISHII, Kazuaki IWASA, Youichi MURAKAMI, Satoru KUNII, Hajime SAGAYAMA, Yusuke WAKABAYASHI, Hiroshi SAWA Department of Physics, Tokyo Metropolitan University, Tokyo 192-0397, Japan Faculty of Science, Tohoku University, Sendai 980-8577, Japan Synchrotron Radiation Research Center, JAERI, Hyogo 679-5148, Japan Photon Factory, Institute for Materials Structure Science, KEK, Tsukuba 305-0801, Japan

hamon, 2012

Interactions between electrons carrying various degrees of freedom are relevant to physical prope... more Interactions between electrons carrying various degrees of freedom are relevant to physical properties and phase transitions in materials. Inelastic neutron spectroscopy for crystal field excitations is meaningful to resolve the electronic interactions. In this article, some example results for rare-earth metallic compounds are briefly shown.

Exploring a Quantum State Hierarchy for f Electrons: Evolution into Electron-Nuclear Hyperfine-Coupled Multiplets via Multipole Ordering

JPSJ News and Comments, 2011

Novel Features Realized in the Filled Skutterudite Structure

Journal of the Physical Society of Japan, 2008

ABSTRACT

Magnetic Excitation in Totally Symmetric Staggered Ordered Phase of PrFe 4 P 12

Journal of the Physical Society of Japan, 2012

We report inelastic neutron scattering results for single-crystalline samples of PrFe 4 P 12 , wh... more We report inelastic neutron scattering results for single-crystalline samples of PrFe 4 P 12 , which undergoes a transition from the heavy-electron phase to the antiferro-type nonmagnetic ordered phase. In contrast to the quasielastic magnetic response observed in the heavy electron phase, the well-defined inelastic peaks located at 1.5 and 3 meV are superimposed in the ordered phase. The maximum spectral intensity appears at the Brillouin zone center for the original I m \bar3 structure, and the minimum spectral intensity appears at the zone boundaries including the ordering vector q 0 =(1,0,0). The evolution of the 1.5 meV peak with an applied magnetic field in the ordered phase is in agreement with excitations between 4 f -electron crystalline-field-splitting levels, while the 3 meV peak is smeared out rapidly. The spectra are consistent with the recently proposed staggered ordering of a Pr site with well-localized f -electrons and that with a Kondo-singlet-like state, which are represented as the tota...

Well-Defined Crystal Field Splitting Schemes and Non-Kramers Doublet Ground States of f Electrons in Pr T 2 Zn 20 ( T = Ir, Rh, and Ru)

Journal of the Physical Society of Japan, 2013

Inelastic neutron scattering studies of Pr$T_{2}$Zn20 ($T$ = Ir, Rh, and Ru) were carried out... more Inelastic neutron scattering studies of Pr$T_{2}$Zn20 ($T$ = Ir, Rh, and Ru) were carried out in order to reveal $f$ electron states indispensable for the low-temperature properties of Pr$T_{2}$Zn20 associated with multipole degrees of freedom. Sharp excitation peaks, which are located within excitation energies of less than 10 meV, are attributed to crystal field splitting level schemes of $4f^{2}$ in Pr3+ ions. Data of the Ir-based compound is explained by a non-Kramers doublet ground state in the local symmetry $T_{d}$ for this system. Results of the Rh-based compound are explained by the scheme for the Pr-site local cubic symmetry $T$ in the low-temperature structural phase, which is lower than $T_{d}$. In the Ru-based compound, the doublet is split as a result of the loss of local cubic symmetry through structural transformation. These experimental results confirm the non-Kramers doublet ground state that causes the quadrupole ordering or orbital Kondo effect predicted for this series...