arXiv subjects

Hiroaki Kadowaki

Publications and source records attributed to Hiroaki Kadowaki.

26 records · Page 2Linked to original sources

arXiv2008

Quantum Phase Transition in the Itinerant Antiferromagnet (V0.9Ti0.1)2O3

Quantum-critical behavior of the itinerant electron antiferromagnet (V0.9Ti0.1)2O3 has been studied by single-crystal neutron scattering. By directly observing antiferromagnetic spin fluctuations in the paramagnetic phase, we have shown that the characteristic energy depends on temperature as c_1 + c_2 T^{3/2}, where c_1 and c_2 are constants. This T^{3/2} dependence demonstrates that the present strongly correlated d-electron antiferromagnet clearly shows the criticality of the spin-density-wave quantum phase transition in three space dimensions.

cond-mat.str-el↗

arXiv2005

Quantum Critical Point of Itinerant Antiferromagnet in Heavy Fermion

A quantum critical point (QCP) of the heavy fermion Ce(Ru_{1-x}Rh_x)_2Si_2 (x = 0, 0.03) has been studied by single-crystalline neutron scattering. By accurately measuring the dynamical susceptibility at the antiferromagnetic wave vector k_3 = 0.35 c^*, we have shown that the energy width Gamma(k_3), i.e., inverse correlation time, depends on temperature as Gamma(k_3) = c_1 + c_2 T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in a low temperature range. This critical exponent 3/2 +- 0.1 proves that the QCP is controlled by that of the itinerant antiferromagnet.

cond-mat.str-el↗

arXiv2005

Quantum Critical Point of Itinerant Antiferromagnet in the Heavy Fermion Ce(Ru_{1-x}Rh_x)_2Si_2

A focus of recent experimental and theoretical studies on heavy fermion systems close to antiferromagnetic (AFM) quantum critical points (QCP) is directed toward revealing the nature of the fixed point, i.e., whether it is an itinerant antiferromagnet [spin density wave (SDW)] type or a locally-critical fixed point. The relevance of the local QCP was proposed to explain the E/T-scaling with an anomalous exponent observed for the AFM QCP of CeCu_{5.9}Au_{0.1}. In this work, we have investigated an AFM QCP of another archetypal heavy fermion system Ce(Ru_{1-x}Rh_x)_2Si_2 with x = 0 and 0.03 (sim x_c) using single-crystalline neutron scattering. Accurate measurements of the dynamical susceptibility Im[chi(Q,E)] at the AFM wave vector Q = 0.35 c^* have shown that Im[chi(Q,E)] is well described by a Lorentzian and its energy width Gamma(Q), i.e., the inverse correlation time depends on temperature as Gamma(Q) = c_1 + c_2 T^{3/2 +- 0.1}, where c_1 and c_2 are x dependent constants, in low temperature ranges.This critical exponent 3/2 proves that the QCP is controlled by the SDW QCP in three space dimensions studied by the renormalization group and self-consistent renormalization theories.

cond-mat.str-el↗

arXiv2005

Rietveld analysis and maximum entropy method of powder diffraction for bundles of single-walled carbon nanotubes

The structure of bundles of single-walled carbon nanotubes (SWNT) has been refined by Rietveld analysis using neutron and X-ray powder diffraction data. Based on previous simulation studies of powder diffraction data of SWNT and standard Rietveld analyses, we have developed a pattern fit technique for SWNT which provides precise structure parameters. We also show that the present technique can be used with the maximum entropy method (MEM), which is complementary to the Rietveld analysis. Using the neutron diffraction data of pristine SWNT, we have successfully reconstructed the density of carbon nuclei and zero density in the inner cavity of SWNT by MEM.

cond-mat.mtrl-sci↗

arXiv2003

Spin Fluctuation in Heavy Fermion CeRu_2Si_2

Spin fluctuations of the archetypal heavy-fermion compound CeRu_2Si_2 have been investigated by neutron scattering in an entire irreducible Brillouin zone. The dynamical susceptibility is remarkably well described by the self-consistent renormalization (SCR) theory of the spin fluctuation in a phenomenological way, proving the effectiveness of the theory. The present analysis using the SCR phenomenology has allowed us to determine fourteen exchange constants, which show the long-range nature of the Ruderman-Kittel-Kasuya-Yosida interaction.

cond-mat.str-el↗

arXiv2002

Neutron Scattering Study of the Spin Correlation in the Spin Ice System Ho2Ti2O7

Intensity distribution of the neutron magnetic scattering has been taken in the reciprocal space of a single crystal of the "spin ice" system Ho2Ti2O7 at the elastic energy position in the temperature (T) region between 0.4 K and 50 K. The short range magnetic correlation becomes appreciable with decreasing T at around 30 K. The freezing of the moment system takes place at around 1.5 K with decreasing T. Based on the mean field treatment of the moment system, the distribution of the observed intensity has been reproduced, where the dipolar interaction is confirmed to be primarily important for the determination of the magnetic correlation. Simple calculations of the scattering intensity carried out by using a cluster of 25 moments of Ho3+ ions indicate that there are many types of the moment arrangement within a cluster which have almost degenerated energies, indicating that the system cannot uniquely select the correlation pattern down to rather low temperature, and before going to the lowest energy state, the system undergoes the gradual slowing down to the glassy state.

cond-mat.str-el↗

arXiv2002

Static Correlation and Dynamical Properties of Tb3+-moments in Tb2Ti2O7 -Neutron Scattering Study-

Static and dynamical properties of the magnetic moment system of pyrochlore compound Tb2Ti2O7 with strong magnetic frustration, have been investigated down to the temperature T=0.4 K by neutron scattering on a single crystal sample. The scattering vector (Q)-dependence of the magnetic scattering intensity becomes appreciable with decreasing T at around 30 K, indicating the development of the magnetic correlation. From the observed energy profiles, the elastic, quasi elastic and inelastic components have been separately obtained. The quasi elastic component corresponds to the diffusive motion of the magnetic moments within the lowest states, which are formed of the lowest energy levels of Tb3+ ions. Magnetic correlation pattern which can roughly reproduce the Q-dependence of the scattering intensities of the elastic and quasi elastic component is discussed based on the trial calculations for clusters of 7 moments belonging to two corner-sharing tetrahedra. A possible origin of the glassy state, which develops at around 1.5 K with decreasing T is discussed.

cond-mat.str-el↗

arXiv2001

Neutron scattering study of dipolar spin ice Ho_2Sn_2O_7: Frustrated pyrochlore magnet

By means of neutron scattering techniques we have investigated the frustrated pyrochlore magnet Ho_2Sn_2O_7, which was found to show a ferromagnetic spin-ice behavior below T \simeq 1.4 K by susceptibility measurements. High-resolution powder-neutron-diffraction shows no detectable disorder of the lattice, which implies appearance of a random magnetic state solely by frustrated geometry, i.e., the corner sharing tetrahedra. Magnetic inelastic-scattering spectra show that Ho magnetic moments behave as an Ising spin system at low temperatures, and that the spin fluctuation has static character. The system remains in a short-range ordered state down to T = 0.4 K. By analyzing the wave-number dependence of the magnetic scattering using a mean field theory, it is clarified that the Ising spins interact via the dipolar interaction. Therefore we conclude that Ho_2Sn_2O_7 belongs to the dipolar-spin-ice family. Slow spin dynamics is exhibited as thermal hysteresis and time dependence of the magnetic scattering.

cond-mat.dis-nn↗