R. Kajimoto

Neutron diffraction study of TbMnO3: Magnetic structure revisited

Magnetic ordering in TbMnO3 was revisited by a neutron diffraction study. In addition to the previously reported A-type and G-type modulated structures with a propagation vector (0,q_Mn,0), we found C-type and F-type orderings of the Mn moments. All the components appear below T_N^Mn = 46 K, and the G, C,and F-type components are enhanced below T_lock = 28 K, where q_Mn ordering locks at its low temperature value. The locking of the propagation vector also yields the squaring up of the spin arrangement. The magnetic moments of Tb ions show a quasi long-range ordering below T_N^Tb = 7 K. It drastically promotes the development of the G, C, and F-type components while suppressing the A-type components.

High-energy spin and charge excitations in electron-doped copper oxide superconductors

The evolution of electronic (spin and charge) excitations upon carrier doping is an extremely important issue in superconducting layered cuprates and the knowledge of its asymmetry between electron- and hole-dopings is still fragmentary. Here we combine X-ray and neutron inelastic scattering measurements to track the doping dependence of both spin and charge excitations in electron-doped materials. Copper L3 resonant inelastic X-ray scattering spectra show that magnetic excitations shift to higher energy upon doping. Their dispersion becomes steeper near the magnetic zone centre and they deeply mix with charge excitations, indicating that electrons acquire a highly itinerant character in the doped metallic state. Moreover, above the magnetic excitations, an additional dispersing feature is observed near the Γ-point, and we ascribe it to particle-hole charge excitations. These properties are in stark contrast with the more localized spin excitations (paramagnons) recently observed in hole-doped compounds even at high doping levels.

High Intensity Chopper Spectrometer 4Seasons At J-parc

Design and performance of a new chopper spectrometer 4SEASONS, which is under construction for the spallation neutron source at Japan Proton Accelerator Research Complex (J-PARC), are described. This spectrometer has middle energy resolution and two orders higher performance than current state-of-the-art chopper spectrometers by utilizing a unique beam transport design and the repetition rate multiplication (RRM) method. 4SEASONS has a specification optimized for the study of the high critical temperature (T c) superconductivity, and should be suitable for collecting weak inelastic signals from a single crystal over a wide four-dimensional (4D) Q-ω space.

ANOMALOUS FERROMAGNETIC SPIN FLUCTUATIONS IN AN ANTIFERROMAGNETIC INSULATOR PR1-XCAXMNO3

The high temperature paramagnetic state in an antiferromagnetic (AFM) insulator Pr_{1-x}Ca_{x}MnO_{3} is characterized by the ferromagnetic (FM) spin fluctuations with an anomalously small energy scale. The FM fluctuations show a precipitous decrease of the intensity at the charge ordering temperature T_{CO}, but persist below T_{CO}, and vanish at the AFM transition temperature T_{N}. These results demonstrate the importance of the spin ordering for the complete switching of the FM fluctuation in doped manganites.

Cold-neutron disk-chopper spectrometer at J-PARC

We are constructing a cold-neutron double-chopper spectrometer for the new spallation neutron source at the Materials and Life Science Facility (MLF), J-PARC. The spectrometer is dedicated to inelastic and quasi-elastic measurements in the cold and thermal neutron incident energy region of E ixa0=xa01-80xa0meV. Looking at a H2-coupled moderator and employing a combination of two fast disk-choppers, one as the pulse-shaping and another as the monochromating chopper, the spectrometer realizes both high intensity and fine resolution. The expected neutron flux at the sample position is of the order of 104-107xa0n/cm2/s depending on E i (e.g. 106xa0n/cm2/s at E ixa0=xa020xa0meV with ΔE/E ixa0=xa03%). The newly developed fast disk-chopper enables a fine and tunable energy resolution (ΔE/E ixa0≥xa01% at E ixa0=xa020xa0meV). A large area detector bank (xa0±xa0135° in horizontal, −xa022-+30° in vertical and 1.3π in solid angle) covers wide momentum transfer range with the resolution of a few percent of ΔQ/k i, where ΔQ is the uncertainty in the long...

Utilization of multiple incident energies on Cold-Neutron Disk-Chopper Spectrometer at J-PARC

Inelastic neutron scattering measurement utilizing the multiple incident energies is a promising method to improve the measurement efficiency of chopper spectrometers at pulsed neutron sources. In this paper, we will show the performance of utilizing the multiple incident energies measurement on Cold-Neutron Disk-Chopper Spectrometer (CNDCS) at J-PARC. The related issues of the instrument design to realize the multiple incident energies measurement will also be mentioned.

Inelastic and quasi-elastic neutron scattering spectrometers in J-PARC ☆

J-PARC, Japan Proton Accelerator Research Complex provides short pulse proton beam at a repetition rate 25Hz and the maximum power is expected to be 1MW. Materials and Life Science Experimental Facility (MLF) has 23 neutron beam ports and 21 instruments have already been operated or under construction/commissioning. There are 6 inelastic/quasi-elastic neutron scattering spectrometers and the complementary use of these spectrometers will open new insight for life science. This article is part of a Special Issue entitled Science for Life Guest Editor: Dr. Austen Angell, Dr. Salvatore Magazù and Dr. Federica Migliardo.

Inelastic neutron scattering study of the magnetic fluctuations in Sr 2 RuO 4

By performing time-of-flight neutron scattering measurements on a large sample of single crystals of Sr

Conceptual Design Of Magic Chopper Used For 4SEASONS at J-PARC

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Designed Performance of High Resolution Chopper Spectrometer at J-PARC

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