Josephson junctions with ferromagnetic barriers have been intensively investigated in recent years. Of particular interest has been the realization of so called π-junctions with a built-in phase difference, and induced triplet pairing. Such experiments have so far been limited to systems containing metallic ferromagnets. Although junctions incorporating a ferromagnetic insulator (I(F)) have been predicted to show a range of unique properties including π-shifts with intrinsically low dissipation and an unconventional temperature dependence of the critical current I(c), difficulties with the few known I(F) materials have prevented experimental tests. Here we report supercurrents through magnetic GdN barriers and show that the field and temperature dependence of I(c)is strongly modified by the I(F). In particular we show that the strong suppression of Cooper pair tunnelling by the spin filtering of the I(F) barrier can be modified by magnetic inhomogeneity in the barrier.
Epitaxial (001)-, (118)-, and (104)-oriented Nd-doped Bi 4 Ti 3 O 12 films have been grown by pulsed-laser deposition from a Bi 4-x Nd x Ti 3 O 12 (x=0.85) target on SrRuO 3 coated single-crystal (100)-, (110)-, and (111)-oriented SrTiO 3 substrates, respectively. X-ray diffraction illustrated a unique epitaxial relationship between film and substrate for all orientations. We observed a strong dependence of ferroelectric properties on the film orientation, with no ferroelectric activity in an (001)-oriented film; a remanent polarization, 2P r , of 12 µC/cm 2 and coercive field, E c , of 120 kV/cm in a (118)-oriented film; and 2P r = 40 µC/cm 2 , E c = 50 kV/cm in a (104)-oriented film. The lack of ferroelectric activity along the c-axis is consistent with the orthorhombic nature of the crystal structure of the bulk material, as determined by powder neutron diffraction.
A model has been developed to account for the dependence of melting temperature on the size of nanosolids (nanoparticles, nanowires and nanofilms). In this model the effect of particle size and shape, lattice and surface packing factor, and the coordination number of the lattice and of the surface crystalline planes are considered. A general equation is proposed, having nonlinear form as a function of the reciprocal of nanosolid size. This model is consistent with reported experimental data for nanoparticles of In and Au, nanowires of Pb and In, and nanofilms of In.
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