We show a simple, robust, chemical route to the fabrication of ultrahigh-density arrays of nanopores with high aspect ratios using the equilibrium self-assembled morphology of asymmetric diblock copolymers. The dimensions and lateral density of the array are determined by segmental interactions and the copolymer molecular weight. Through direct current electrodeposition, we fabricated vertical arrays of nanowires with densities in excess of 1.9 x 10(11) wires per square centimeter. We found markedly enhanced coercivities with ferromagnetic cobalt nanowires that point toward a route to ultrahigh-density storage media. The copolymer approach described is practical, parallel, compatible with current lithographic processes, and amenable to multilayered device fabrication.

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We report on the fabrication of a new class of trilayer epitaxial thin film devices based on the doped perovskite manganates La–Ca–Mn–O and La–Sr–Mn–O. We show that large resistance changes, up to a factor of 2, can be induced by a moderate applied magnetic field below 200 Oe in these trilayers supporting current-perpendicular-to-plane transport. These results show that low-field spin-dependent transport in manganates can be accomplished, the magnitude of which is suitable for magnetoresistive field sensors.

Nanotubes and nanowires with both elemental (carbon or silicon) and multi-element compositions (such as compound semiconductors or oxides), and exhibiting electronic properties ranging from metallic to semiconducting, are being extensively investigated for use in device structures designed to control electron charge. However, another important degree of freedom--electron spin, the control of which underlies the operation of 'spintronic' devices--has been much less explored. This is probably due to the relative paucity of nanometre-scale ferromagnetic building blocks (in which electron spins are naturally aligned) from which spin-polarized electrons can be injected. Here we describe nanotubes of vanadium oxide (VO(x)), formed by controllable self-assembly, that are ferromagnetic at room temperature. The as-formed nanotubes are transformed from spin-frustrated semiconductors to ferromagnets by doping with either electrons or holes, potentially offering a route to spin control in nanotube-based heterostructures.

Interlayer tunneling resistivity is used to probe the low-energy density-of-states (DOS) depletion due to the pseudogap in the normal state of Bi2Sr2CaCu2O8+y. Measurements up to 60 T reveal that a field that restores DOS to its ungapped state shows strikingly different temperature and doping dependencies from the characteristic fields of the superconducting state. The pseudogap closing field and the pseudogap temperature T ⋆ evaluated independently are related through a simple Zeeman energy scaling. These findings indicate a predominant role of spins over the orbital effects in the formation of the pseudogap.PACS numbers: 74.25. Dw, 74.25.Fy, 74.50.+r, 74.72.Hs A central unresolved issue of high temperature superconductivity is the connection of normal state correlations, referred to as the pseudogap [1][2][3][4][5], to the origins of high-T c . At the heart of the debate [6-11] is whether the pseudogap, which manifests itself as a depletion of the quasiparticle density of states (DOS) below a characteristic temperature T ⋆ , originates from spin or charge degrees of freedom and, in particular, whether it derives from some precursor of Cooper pairing [12] that acquires the superconducting coherence at T c . Energies of the order of the pseudogap have been accessed with elevated temperatures, with applied voltage in tunneling measurements, and with infrared frequencies in optical spectra [1]. But little is known about the effect of magnetic field. The magnetic field response may be unique: e.g., in the case of the superconducting state the upper critical field H c2 is determined by the superconducting coherence length, and not directly by the superconducting gap, since magnetic field strongly couples to the orbital motion of Cooper pairs.Current knowledge about the field dependence of the pseudogap derived from spectroscopic measurements is partly limited by the available dc field range [7][8][9][10][11]. More importantly, there is no systematic doping dependence in a single family of cuprates. Even in optimally doped YBa 2 Cu 3 O 7−δ alone, based on NMR relaxation rate measurements below 27.3 T, the pseudogap was claimed to decrease [7] or be independent of magnetic field [8]. In the underdoped YBa 2 Cu 4 O 8 no field effect on T ⋆ was reported up to 23.2 T [9], while a recent NMR study indicated a measurable field dependence in slightly overdoped TlSr 2 CaCu 2 O 6.8 [10]. In this paper, we report the interlayer (c-axis) resistivity ρ c measurements in fields up to 60 T in Bi 2 Sr 2 CaCu 2 O 8+y (BSCCO) crystals in a wide range of doping, from which we make a first systematic evaluation of the pseudogap closing field H pg that restores DOS to its ungapped state. Our results indicate a pronounced difference between field-temperature (H-T ) diagrams of the pseudogap and the superconducting states and a simple Zeeman scaling between H pg (0) and T ⋆ . Among various techniques that quantify DOS, the ρ c measurements are uniquely suited for exploring the highest magnetic field range available only in a pulsed mod...