Junichiro Wada

Preparation of single crystal of Ca2CuO3 by TSFZ method

Abstract A bulky (7×3×3 mm 3 ) single crystal fo Ca 2 CuO 3 has been successfully prepared by the traveling-solvent-floating-zone (TSFZ) method using CuO excess solvent. An optimum solvent composition for growth of the titled compound was found to be around 9 in CuO/CaO molar ratio R under 0.1 MPa oxygen partial pressure. The obtained R value considerably deviates from the estimated one based on the reported equilibrium phase diagrams. Anisotropic magnetic susceptibilities of the prepared single crystal were observed. In particular an anomalous thermal behaviour of the susceptibility under the magnetic field along [001] and [010] indicates an appearance of three-dimensional antiferromagnetic order below around 8 K.

Hole Doping Effect on 2D Spin Correlations in La2NiO4+δ

Quasielastic neutron scattering experiments from La 2 NiO 4+δ revealed a substantial hole doping effect on the 2 dimensional spin correlations. Thermal evolution of correlation length clearly shows the reduction of the exchange stiffness constant by hole doping, which is in marked contrast to that of La 2 CuO 4+δ . The present result is reflected by the hole character in La 2 NiO 4+δ , which is different from that in the cuprate.

Spatial modulation of low-frequency spin fluctuations in hole-doped La2CuO4

Systematic neutron scattering measurements have been performed on the Sr-doped La{2-x}SrxCuO4 to study the doping dependence of spatially modulated dynamical spin correlations or so-called incommensurate spin fluctuations. The modulated spin correlations appear beyond x ≈ 0.05 which is close to the lower boundary of the superconducting phase. First evidence was observed for the linear relation between the degree of spatial modulation or the incommensurability Σ(x) and the maximumTc atx. We present a universal curve for Σ(x) by adding data from other La2CuO2 systems such as oxygen-doped superconductors, oxygen-reduced or Zn-substituted nonsuperconductors, and La1.6-xNd0.4SrxCuO4.

Antiferromagnetic long range order of the S = 12 linear chain cuprate Ca2CuO3

Abstract Neutron scattering measurements have been performed on a single crystal of Ca 2 CuO 3 , an S = 1 2 quasi-one-dimensional (ID) antiferromagnet. A three-dimensional (3D) antiferromagnetic long range order was observed below 8 K with an antiparallel Cu spin alignment within the CuO chain and between the nearest neighbor spins on the different chains. The anomalously small ordered moment of about 0.05 μ B might originate from the large energy scale of the spin fluctuation.

Neutron Scattering Study of Oxygen Ordering and Magnetic Correlations in La 2NiO 4.11 and La 2NiO 4.125

We have performed neutron scattering experiments on single crystals of La 2 NiO 4+δ (δ=0.11, and 0.125) to study the effect of oxygen doping on the structural and magnetic properties. The degree of the excess oxygen order strongly influences the local crystal structure and interlayer magnetic correlation. The intralayer magnetic correlation is depressed by doping in the commensurate region (δ≤0.11), then turns to increase in the incommensurate region (δ>0.11). Our experimental results are compared with existing results for oxygen and Sr doped La 2 NiO 4 .

Spin-phonon interactions in the Raman spectra of one- and two-dimensional quantum spin antiferromagnets

Abstract Two-magnon Raman scattering in one-dimensional S = ½ quantum spin antiferromagnets Ca2CuO3 and CuGeO3 is found to extend up to 2πJ, where J is the exchange energy along the chain. The resonant multi-phonon peaks in Ca2CuO3 and undoped high Tc cuprates, and phonon peaks related to the spin-Peierls transition in CuGeO3 are highly asymmetric in the spin-phonon interactions, if the phonon energies are within the two-magnon band and polarizations of incident and scattered light are parallel to each other and to the chain or plane.