Jianglin Feng

Giant magnetoresistance in a low-temperature GaAs/MnAs nanoscale ferromagnet hybrid structure

We report the observation of a giant magnetoresistance effect in a low-temperature (LT-)GaAs/MnAs nanoscale ferromagnet hybrid structure. The MnAs nanomagnets are formed by ion implantation of Mn into LT GaAs and subsequent annealing. We have studied the magnetotransport using a vertically biased p+-GaAs/LT-GaAs:MnAs/p+-GaAs structure. A negative magnetoresistance (Δρ/ρ=[ρ(B)−ρ(0)]/ρ(0)) of up to −80% (B=7 T) is observed at low temperatures (T<20 K), which changes its sign from negative to positive between T=15 K and T=20 K. The value of the positive magnetoresistance decreases with increasing temperature from +115% (20 K) to +1.4% (300 K). The magnetoresistance variations with B and T are correlated with the nanomagnet spacing in the structure.

MORPHOLOGY DEFINITION BY DISCLINATIONS AND DISLOCATIONS IN A MESOSTRUCTURED SILICATE CRYSTAL

Curved surface morphologies resulting from disclinations are unusual in inorganic phases because the relatively large lattice energies generally permit only translational dislocations. In this letter, we show, however, that disclinations can be readily observed and identified in composite organic/inorganic phases. Disclinations and dislocations in MCM-41, a two-dimensional hexagonal (p6mm) mesophase crystal synthesized using silicate and surfactant precursors, were investigated by using transmission electron microscopy. We observed two types of dislocations and two types of disclinations. All dislocations observed are of the smallest Burgers vector a (the basis vector). Dislocation dipoles and disclination quadrupoles appear more frequently than isolated ones.

Due to an error in printing, the following article, originally published in the 4 August 1997 issue, is being republished in its entirety. Morphology definition by disclinations and dislocations in a mesostructured silicate crystal

Curved surface morphologies resulting from disclinations are unusual in inorganic phases because the relatively large lattice energies generally permit only translational dislocations. In this letter, we show, however, that disclinations can be readily observed and identified in composite organic/inorganic phases. Disclinations and dislocations in MCM-41, a two-dimensional hexagonal (p6mm) mesophase crystal synthesized using silicate and surfactant precursors, were investigated by using transmission electron microscopy. We observed two types of dislocations and two types of disclinations. All dislocations observed are of the smallest Burgers vector a (the basis vector). Dislocation dipoles and disclination quadrupoles appear more frequently than isolated ones.

Formation and Properties of Nanosize Ferromagnetic MnAs Particles in Low Temperature GaAs by Manganese Implantation

The synthesis of ferromagnetic particles of the size of several nm (10… 100nm) imbedded in semiconductors is of particular interest for device applications such as magnetic sensors, switches or memories based on integrated semiconductor devices. We have investigated the formation as well as the structural and magnetic properties of MnAs nanomagnets ( size ≈ 20nm) in low temperature grown GaAs (LT-GaAs). The MnAs nanomagnets which show ferromagnetism at room temperature have been synthesized using ion implantation with Mn and subsequent rapid thermal annealing (RTA). To characterize these nanomagnets, we present SQUID measurements (superconducting quantum interference device), TEM analysis (transmission electron microscopy) and EDX analysis (electron beam induced x-ray fluorescence).

Synthesis and characterization of mesostructured aluminophosphatesusing the fluoride route

The room-temperature synthesis of the hexagonal mesostructured aluminophosphate and its phase transition into the lamellar phase are reported.