7,270 research outputs found

    Collinear-to-Spiral Spin Transformation without Changing Modulation Wavelength upon Ferroelectric Transition in Tb1-xDyxMnO3

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    Lattice modulation and magnetic structures in magnetoelectric compounds Tb1-xDyxMnO3 have been studied around the ferroelectric (FE) Curie temperature T_C by x-ray and neutron diffraction. Temperature-independent modulation vectors through T_C are observed for the compounds with 0.50< x < 0.68. This indicates that ferroelectricity with a polarization (P) along the c axis in the RMnO3 series cannot be ascribed to such an incommensurate-commensurate transition of an antiferromagnetic order as was previously anticipated. Neutron diffraction study of a single crystal with x=0.59 shows that the FE transition is accompanied by the transformation of the Mn-spin alignment from sinusoidal (collinear) antiferromagnetism into a transverse spiral structure. The observed spiral structure below T_C is expected to produce P along the c axis with the `inverse' Dzialoshinski-Moriya interaction, which is consistent with the observation.Comment: 9 pages, 4 figure

    Internal magnetic field effect on magnetoelectricity in orthorhombic RMnO3RMnO_3 crystals

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    We have investigated the role of the 4ff moment on the magnetoelectric (ME) effect of orthorhombic RRMnO3_{3} (RR=rare earth ions). In order to clarify the role of the 4ff moment, we prepared three samples: (Eu,Y)MnO3_{3} without the 4ff moment, TbMnO3_{3} with the anisotropic 4ff moment, and (Gd,Y)MnO3_{3} with the isotropic 4ff moment. The ferroelectric behaviors of these samples are different from each other in a zero magnetic field. (Eu,Y)MnO3_{3} and (Gd,Y)MnO3_{3} show the ferroelectric polarization along the a axis in the ground state, while TbMnO3_{3} shows it along the c axis. Such difference may arise from the influence of the anisotropic Tb3+^{3+} 4ff moment. The direction of the ferroelectric polarization of RRMnO3_{3} is determined by the internal magnetic field arising from the 4ff moment.Comment: 2 pages, 1 figure, the proceeding of International Conference of Magnetism, to be published in the Journal of Magnetism and Magnetic Material

    Effect of disorder outside the CuO2_{2} planes on TcT_{c} of copper oxide superconductors

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    The effect of disorder on the superconducting transition temperature TcT_{c} of cuprate superconductors is examined. Disorder is introduced into the cation sites in the plane adjacent to the CuO2_{2} planes of two single-layer systems, Bi2.0_{2.0}Sr1.6_{1.6}Ln0.4_{0.4}CuO6+δ_{6+\delta} and La1.85−y_{1.85-y}Ndy_{y}Sr0.15_{0.15}CuO4_{4}. Disorder is controlled by changing rare earth (Ln) ions with different ionic radius in the former, and by varying the Nd content in the latter with the doped carrier density kept constant. We show that this type of disorder works as weak scatterers in contrast to the in-plane disorder produced by Zn, but remarkably reduces TcT_{c} suggesting novel effects of disorder on high-TcT_{c} superconductivity.Comment: 5 pages, 5 figures, to be published in Phys. Rev. Let

    Antiproton Production in p+d Reaction at Subthreshold Energies

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    An enhancement of antiprotons produced in p+d reaction in comparison with ones in p+p elementary reaction is investigated. In the neighborhood of subthreshold energy the enhancement is caused by the difference of available energies for antiproton production. The cross section in p+d reaction, on the other hand, becomes just twice of the one in elementary p+p reaction at the incident energy far from the threshold energy when non-nucleonic components in deuteron target are not considered.Comment: LaTeX,7 pages with 5 eps figure

    Volume, Coulomb, and volume-symmetry coefficients of nucleus incompressibility in the relativistic mean field theory with the excluded volume effects

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    The relation among the volume coefficient KK(=incompressibility of the nuclear matter), the Coulomb coefficient KcK_c, and the volume-symmetry coefficient KvsK_{vs} of the nucleus incompressibility are studied in the framework of the relativistic mean field theory with the excluded volume effects of the nucleons, under the assumption of the scaling model. It is found that K=300±50K= 300\pm 50MeV is necessary to account for the empirical values of KK, KcK_c, and KvsK_{vs}, simultaneously, as is in the case of the point-like nucleons. The result is independent on the detail descriptions of the potential of the σ\sigma-meson self-interaction and is almost independent on the excluded volume of the nucleons.Comment: PACS numbers, 21.65.+f, 21.30.+

    Compressional properties of nuclear matter in the relativistic mean field theory with the excluded volume effects

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    Compressional properties of nuclear matter are studied by using the mean field theory with the excluded volume effects of the nucleons. It is found that the excluded volume effects make it possible to fit the empirical data of the Coulomb coefficient KcK_{c} of nucleus incompressibility, even if the volume coefficient KK is small(∼150\sim 150MeV). However, the symmetry properties favor K=300±50K=300\pm 50MeV as in the cases of the mean field theory of point-like nucleons.Comment: PACS numbers, 21.65.+f, 21.30.+
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