One of the leading issues in high-T(c) superconductors is the origin of the pseudogap phase in underdoped cuprates. Using polarized elastic neutron diffraction, we identify a novel magnetic order in the YB(2)Cu(3)O(6+) system. The observed magnetic order preserves translational symmetry of the lattice as proposed for orbital moments in the circulating current theory of the pseudogap state. To date, it is the first direct evidence of a hidden order parameter characterizing the pseudogap phase in high-T(c) cuprates.

Using elastic neutron scattering, we evidence a commensurate antiferromagnetic Cu(2) order (AF) in the superconducting (SC) high-$\rm T_c$ cuprate $\rm YBa_2(Cu_{1-y}Co_y)_3O_{7+\delta}$ (y=0.013, $\rm T_c$=93 K). As in the Co-free system, the spin excitation spectrum is dominated by a magnetic resonance peak at 41 meV but with a reduced spectral weight. The substitution of Co thus leads to a state where AF and SC cohabit showing that the CuO$_2$ plane is a highly antiferromagnetically polarizable medium even for a sample where T$_c$ remains optimum.Comment: 3 figure

A large inverse magnetocaloric effect has been observed in a Ni45Co5Mn37.5In12.5 single crystal at room temperature. Magnetothermal measurements performed at different magnetic fields reveal a nonmagnetic to ferromagnetic transition correlated with the austenite-martensite phase transformation. The Heusler single crystal shows a large entropy change of 30 J/Kg K at an applied magnetic field of 7 T during the first-order magnetostructural transition at 355 K. It leads to a net refrigerant capacity of 267 J/Kg at 7 T, which is very encouraging for magnetic refrigeration applications.

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Engineering applications of carbon nanofibers and nanotubes require their alignment in specific directions. Single-walled carbon nanotubes can be aligned in a magnetic field due to the presence of small amounts of catalyst elements, such as Ni and Co. However, for carbon nanofibers, their extremely low magnetic susceptibility is not sufficient for magnetically induced alignment. We present a method of solution-coating of NiO and CoO onto the surface of the carbon nanofibers. Due to the NiO-and CoO-coating, these nanofibers can be well aligned in the polymer composites under moderate magnetic field ͑3 T͒. Both transmission electron microscopy and scanning electron microscopy results show the well-aligned nanofibers in a polymer matrix. Mechanical testing shows a pronounced anisotropy in tensile strength in directions normal ͑12.1 MPa͒ and parallel ͑22 MPa͒ to the applied field, resulting from the well-aligned nanofibers in the polymer matrix. The mechanism of magnetic alignment due to coating of NiO and CoO on the nanofiber surface is discussed.

The response in capacitance to low external magnetic fields (up to 0.1 T) of suspensions of spherical magnetic nanoparticles, single-wall carbon nanotubes (SWCNT), SWCNT functionalized with carboxyl group (SWCNT-COOH) and SWCNT functionalized with Fe 3 O 4 nanoparticles in a nematic liquid crystal has been studied experimentally. The volume concentration of nanoparticles was φ 1 = 10 −4 and φ 2 = 10 −3 . Independent of the type and the volume concentration of the nanoparticles, a linear response to low magnetic fields (far below the magnetic Fréederiksz transition threshold) has been observed, which is not present in the undoped nematic.

In this study, observations of structural transitions in ferronematics based on the thermotropic nematic 4-trans-4 -n-hexyl-cyclohexyl-isothiocyanato-benzene (6CHBT) are described. Droplets of the nematic phase in the isotropic phase were observed in solutions of nematogenic 6CHBT dissolved in phenyl isocyanate and 6CHBT dissolved in phenyl isocyanate and doped with magnetic particles of different shapes (nanorods and chain-like particles). Magneto-dielectric measurements of structural transitions in these new systems enable to estimate of the type of anchoring of the nematic molecules on the magnetic particles surface.

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