Daichi Kawana

Neutron Brillouin Scattering with Pulsed Spallation Neutron Source —Spin-Wave Excitations from Ferromagnetic Powder Samples—

The neutron Brillouin scattering (NBS) method, which was developed using advanced neutron sources, was extended to an intense pulsed spallation neutron source. The feasibility of this method was demonstrated by observing ferromagnetic spin waves in La0.8Sr0.2MnO3 and SrRuO3 powders. Gapless spin-wave excitations were observed in La0.8Sr0.2MnO3, which were continuously extrapolated to the lower scattering vector \(Q\) from previous results using single crystals. The novel result is a well-defined quadratic \(Q\) dependence in the spin-wave dispersion curve with a large energy gap in SrRuO3.

Structural Transformation on the Pressure-Induced Metal–Insulator Transition in PrFe4P12

We report the first X-ray diffraction experiments of PrFe 4 P 12 under high pressure. We discovered a symmetry lowering from cubic to orthorhombic or lower at the metal–insulator transition temperature, accompanied by a jump in the lattice constant, which indicates a first-order phase transition. The superlattice reflections at q =(1,0,0) observed in the low-pressure nonmagnetic ordered phase are found to disappear in the insulating phase. The temperature dependence of the lattice constant and the absence of the superlattice reflections are well explained by taking into account an antiferromagnetic ordering.

Pressure-Induced Antiferromagnetic Order in Filled Skutterudite PrFe4P12 Studied by Single-Crystal High-Pressure Neutron Diffraction

The order parameter in the pressure-induced insulating phase of the filled skutterudite compound PrFe 4 P 12 has been investigated using a high-pressure single-crystal neutron diffraction technique. Clear evidence of the antiferromagnetic order with the propagation vector q = (1, 0, 0) was observed in the insulating phase above 2.7 GPa. The q = (1, 0, 0) structure is identical with that in the nonmagnetic ordered phase below 2.5 GPa and with the nesting property of the Fermi surface. The observed magnetic moment of the Pr ion is 2 µ B and almost pressure-independent up to at least 4.2 GPa. The 2 µ B magnetic moment originates from the dipole in the low-lying quasi-quartet crystal field state. The pressure-induced antiferromagnetic structure at 3.2 GPa is suppressed by applying a magnetic field of about 1.5 T, which is interpreted as a flop of magnetic moments into the alignment of the ferromagnetic state. This brings about a steep decrease in the electrical resistivity due to the disappearance of the anti...

Neutron Brillouin Scattering Experiments with Pulsed Neutrons on High Resolution Chopper Spectrometer HRC

We improved the High Resolution Chopper Spectrometer (HRC), which is installed at MLF in J-PARC, in order to perform neutron Brillouin scattering (NBS) experiments, and successfully demonstrated a feasibility of this method. Gapless spin-wave excitations were observed in La0.8Sr0.2MnO3, which were in good agreement with previous results using single crystals, on the other hand, a large energy gap in the ferromagnetic spin waves was found in SrRuO3. Spin-wave peaks in a permanent magnet Nd2Fe14B were on the dispersion curve determined previously using a single crystal. Excitations, so-called fast sound, in liquid D2O were in a good agreement with previous inelastic neutron scattering experiments and the dispersion curve were extended to the lower Q region.

Observation of spin-wave dispersion in Nd-Fe-B magnets using neutron Brillouin scattering

The low-energy spin-wave dispersion in polycrystalline Nd-Fe-B magnets was observed using neutron Brillouin scattering (NBS). Low-energy spin-wave excitations for the lowest acoustic spin-wave mode were clearly observed. From the spin-wave dispersion, we were able to determine the spin-wave stiffness constant Dsw (100.0 ± 4.9 meV.A2) and the exchange stiffness constant A (6.6 ± 0.3 pJ/m).

Dynamical Properties of Spins and Holes in Carrier Doped Quantum Haldane Chain

Quantum spins in one-dimensional (1D) chains exhibit characteristic features such as the Haldane gap (S=1) and the spin-Peierls state (S=1/2). Recently multi degrees of freedom in cooperation with quantum spins are focused. We present here spin dynamics in the lightly hole doped Nd2-xCaxBaNiO5 (x=0.035), 1D Haldane system by means of pulsed neutron inelastic scattering method. One-magnon band with a spin gap (Haldane gap) was visible with the decrease of the zone boundary energy to 60 meV. In contrast, the spin gap slightly increases. Dynamical structures inside spin gap upon carrier doping showing incommensurate structure centered at the magnetic zone center was newly observed which is possibly originating from the doped holes in Haldane chains.

Quantum Renormalization Effect in One-Dimensional Heisenberg Antiferromagnets

The dispersion relations of the lowest magnetic excitations at low temperatures and the temperature dependence of the inverse magnetic correlation length were determined using inelastic pulsed neutron scattering experiments on the following one-dimensional Heisenberg antiferromagnets: CsVCl 3 ( S = 3/2), CsVBr 3 ( S = 3/2), CsCrCl 3 ( S = 2), and CsNiCl 3 ( S = 1). From studying the exchange constant, J , it has been found that the observed energies of the magnetic excitations require a quantum renormalization factor that is dependent on the spin quantum number, S . The values of J were determined from the temperature dependence of the inverse magnetic correlation length, which describes the static correlation function that can be deduced from the energy-integrated dynamical structure factor. We demonstrated that the S -dependent quantum renormalization effect was detected by only inelastic pulsed neutron scattering experiments, and that the effect was consistent with quantum Monte Carlo calculations.

Experimental confirmation of spin gap in antiferromagnetic alternating spin- 3 2 chain substances R CrGeO 5 ( R = Y or Sm 154 ) by inelastic neutron scattering experiments

A spin-singlet ground state with a spin gap has been discovered in antiferromagnetic spin chain substances when the spin value is 1/2, 1, or 2. To find spin-gap (singlet-triplet) excitations in spin-

Substitution effect on the multipolar transitions in Pr(FexRu1- x)4P12

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Science from the Initial Operation of HRC

chain substances, we performed inelastic neutron scattering and magnetization measurements on