Two- and three-dimensional superlattices of passivated cobalt nanoparticles were formed by a self-assembly technique. The size and stabilization of the cobalt nanoparticles are controlled by using the combination of oleic acid and triphenylphosphine. The cobalt nanoparticles are stable for at least 90 days without oxidation at room temperature under ambient conditions. The magnetic properties of the cobalt nanoparticles in different forms are compared, which provides helpful information on the magnetostatic interaction of the nanoparticles.

A new method was found to synthesize large-area (7 × 15 mm2), high-density (higher than 109 cm−2), aligned carbon nanotubes (CNTs) with uniform diameters on a silica wafer. Ferrocene/melamine mixtures were pyrolyzed through a three-step process in an Ar atmosphere in a single-stage furnace. The structure and composition of the CNTs were investigated by scanning electron microscopy, transmission electron microscopy (TEM), x-ray photoelectron spectroscopy (XPS), and electron energy-loss spectroscopy (EELS). It was found that these nanotubes have uniform outer diameters of about 22 nm and varying lengths from 10 to 40 μm. High-resolution TEM images showed that CNT is composed of graphite-like layers arranged in a stacked-cup-like structure. XPS results showed that the layer covering the tops of the aligned CNTs consists of carbon and iron. The EELS spectrum showed that these tubes are pure carbon.

The polarity of the ZnO film grown on sapphire using an ultrathin Ga wetting layer has been investigated by electron holography. Spontaneous polarization of the ZnO film leads to localized charges in the surface, which change the potential distribution in the vacuum side of the film. The potential distribution depends on the nature of the bounded charges and change as a function of the distance from the film surface. By studying the dependence of the potential change on the distance from the film surface, the ZnO film with very thin Ga wetting layer is determined to have the [0001] polarity.

A systematic investigation of structure and intrinsic magnetic properties of the novel compounds R 3 ͑Fe, T͒ 29 ͑RϭY, Ce, Nd, Sm, Gd, Tb, and Dy; TϭV and Cr͒ has been performed. The lattice constants and unit cell volume decrease with increasing the rare-earth atomic number from RϭNd to Dy, except for Ce, reflecting the lanthanide contraction. The Curie temperature increases from RϭCe to Gd and decreases from Gd to Dy, respectively, with increasing atomic number and Gd 3 Fe 29Ϫx T x has the highest Curie temperature for each series of R 3 Fe 29Ϫx T x ͑TϭV or Cr͒ compounds. The saturation magnetization of R 3 Fe 29Ϫx T x at 4.2 K decreases gradually from RϭNd to Dy with increasing atomic number, except for Ce, in each series of R 3 Fe 29Ϫx T x . It is suggested that the Ce ion in Ce 3 Fe 29Ϫx T x is valence fluctuated which leads to the unusual magnetic properties. The spin reorientations of the easy magnetization direction of R 3 Fe 29Ϫx T x are observed at around 230, 230, and 160 K for RϭNd, Sm, and Tb when TϭV, and at around 230 and 180 K for RϭNd and Tb when TϭCr, respectively. First order magnetization processes are observed around 5.7 T for Sm 3 Fe 26.7 V 2.3 and 4 T for Sm 3 Fe 24.0 Cr 5.0 at 4.2 K, 2.0 T for Tb 3 Fe 28.0 V 1.0 , and 2.3 T for Tb 3 Fe 28.0 Cr 1.0 at room temperature. A phenomenological analysis shows that the saturation magnetization of R 3 Fe 29Ϫx T x compounds with a low T concentration can be roughly calculated based on a combination of those of the 2:17R and 1:12 units in a ratio of 1:1.

Transmission Electron Microscopy evidence of the growth of a magnetite layer acting as a spin filter in CoFe ∕ Al 2 O 3 ∕ CoFe magnetic tunnel junctions Transmission electron microscopy, high-resolution electron microscopy, and electron holography were used to study the microstructure of CoFe/AlO x /Co magnetic tunnel junctions ͑MTJs͒ isochronally annealed up to 400°C. A potential barrier across the metal/oxide interfaces was observed for the as-deposited MTJ sample, and was changed into a well for the MTJ samples annealed at 200 and 400°C, respectively. A shallow potential well was found when the MTJ was annealed at 200°C and the well became deeper as the annealing temperature increased to 400°C. The potential change may attribute to the formation of nonmagnetic metallic Al atoms or clusters when the MTJ sample was annealed at 200°C and the rest content of the barrier layer was more close to Al 2 O 3 , which results in the enhancement of tunneling magnetoresistance ͑TMR͒. When the MTJ sample was annealed at 400°C, more Co and Fe atoms or clusters might diffuse from the ferromagnetic layers into the barrier layer, resulting in the deeper well, and thus significantly decrease the TMR value due to the severe spin-flip scattering.