We report the growth of GdN thin films and a study of their structure and magnetic and conducting properties. It is demonstrated that they are semiconducting at ambient temperature with nitrogen vacancies the dominant dopant. The films are ferromagnetic below 68 K, and a significant narrowing of the band gap is signaled by more than a doubling of its conductivity. The conductivity in the low-temperature ferromagnetic state remains typical of a doped semiconductor, supporting the view that this material is semiconducting in its ground state and that no metal-insulator transition occurs at the Curie temperature.

The depression of T c with fraction y of Zn substitution is studied across the underdoped and overdoped regions in La-214 and (Y,Ca)-123. The overdoped region is well described by elastic scattering at the unitarity limit with a d-wave strong-coupling superconducting order parameter. The underdoped region shows a marked increase in dT c ͞dy, consistent with unitary scattering in the presence of an anisotropic normal-state pseudogap which depletes the density of states about E F . [S0031-9007(97)

The electric hyperfine interaction observable in atomic spectroscopy for O and Cu ions in various configurations is used to analyze the quadrupole splitting of O and Cu nuclear magnetic resonance ͑NMR͒ in La 2Ϫx Sr x CuO 4 and YBa 2 Cu 3 O 6ϩy and to determine the hole densities at both sites as a function of doping. It is found that in La 2Ϫx Sr x CuO 4 all doped holes ͑x͒ reside in the Cu-O plane, but almost exclusively at O. For YBa 2 Cu 3 O 6ϩy and yϽ0.6 doped holes are found at planar Cu as well as O. For yϾ0.6 further doping increases the hole content only for planar O. The phase diagram based on NMR data is presented. Further implications from the Cu A and B sites in La 2Ϫx Sr x CuO 4 and the two planar O sites in YBa 2 Cu 3 O 6ϩy and consequences for the phase diagram are discussed.

This Communication describes the synthesis of highly monodispersed 12 nm nickel nanocubes. The cubic shape was achieved by using trioctylphosphine and hexadecylamine surfactants under a reducing hydrogen atmosphere to favor thermodynamic growth and the stabilization of {100} facets. Varying the metal precursor to trioctylphosphine ratio was found to alter the nanoparticle size and shape from 5 nm spherical nanoparticles to 12 nm nanocubes. High-resolution transmission electron microscopy showed that the nanocubes are protected from further oxidation by a 1 nm NiO shell. Synchrotron-based X-ray diffraction techniques showed the nickel nanocubes order into [100] aligned arrays. Magnetic studies showed the nickel nanocubes have over 4 times enhancement in magnetic saturation compared to spherical superparamagnetic nickel nanoparticles.