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    Magnetic structure, phase diagram, and a new type of spin-flop transition dominated by higher order interaction in a localized 5f system U3Pd20Si6

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    The magnetic structure of the localized-5f uranium intermetallic compound U3Pd20Si6 has been determined by means of a neutron diffraction experiment. Our data demonstrate that this compound has a collinear coupling of the sublattice ordering of the uranium spins on the 4a and 8c sites. We conclude that higher-order exchange and/or quadrupole interactions are necessary to stabilize this unique collinear structure. We discovered a new type of spin-flop transition against the uniaxial anisotropy induced by this collinear coupling

    Pressure-induced Superconductivity in a Ferromagnet UGe2_2 -- Resistivity Measurements in Magnetic Field --

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    The electrical resistivity measurements in the magnetic field are carried out on the pressure-induced superconductor UGe2_2. The superconductivity is observed from 1.06 to 1.44 GPa. The upper critical field of HC2H_{C2} is anisotropic where HC2(T)H_{C2}(T) exhibits positive curvature for H//bH//b and cc-axis. The characteristic enhancement of HC2H_{C2} is reconfirmed for H//aH//a-axis. In the temperature and field dependence of resistivity at P>PCP > P_{C} where the ferromagnetic ordering disappears, it is observed that the application of the external field along the {\it a}-axis increases the coefficient of Fermi liquid behavior AT2AT^{2} correspondingly to the metamagnetic transition.Comment: To be published in the proceeding of the International Conference on High Pressure Science and Technology(AIRAPT-18),Beijing,China,23-27 July 200

    Flux Line Lattice Melting and the Formation of a Coherent Quasiparticle Bloch State in the Ultraclean URu2_2Si2_2 Superconductor

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    We find that in ultraclean heavy-fermion superconductor URu2_2Si2_2 (Tc0=1.45T_{c0}=1.45 K) a distinct flux line lattice melting transition with outstanding characters occurs well below the mean-field upper critical fields. We show that a very small number of carriers with heavy mass in this system results in exceptionally large thermal fluctuations even at subkelvin temperatures, which are witnessed by a sizable region of the flux line liquid phase. The uniqueness is further highlighted by an enhancement of the quasiparticle mean free path below the melting transition, implying a possible formation of a quasiparticle Bloch state in the periodic flux line lattice.Comment: 5 pages, 4 figures, accepted for publication in Phys. Rev. Let
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