Electrodeposited, GMR CoNiFeCu nanowires and nanotubes from electrolytes maintained at different temperatures

Nanowires and nanotubes with modulated composition to realize a magnetoresistance effect were potentiostatically electrodeposited into alumina nanoporous templates. The multilayers were modulated between a Co-rich alloy and a Cu layer. The structure was characterized by electron microscopy. Deposits obtained from room temperature and 50°C electrolytes were nanowires, and a giant magnetoresistance (GMR) of up to 20% was observed. Chilling the electrolyte to 4°C resulted in nanotubes with a modulated structure. The current-potential behavior was examined with voltammetry and pulse transients. As expected, the cathodic current density increases with electrolyte temperature, although less obvious is the unfavorable anodic component, resulting during the transition between depositing the magnetic layer and a copper layer, which changes with time and differs with variable electrolyte temperature. © 2010 The Electrochemical Society

Synthesis and magnetic behavior of ultra-small bimetallic FeCo/graphite nanoparticles

FeCo-alloy graphite-coated nanoparticles with mean particle diameter under 8 nm have been synthesized following a CVD carbon-deficient method. The superior magnetic properties of FeCo-alloy nanoparticles makes them good candidates to be used as magnetic filler in magneto-polymer composites. Thanks to the protective effect of the graphite shell, FeCo nanoparticles are stable under oxygen atmosphere up to 200 ° C. The as-prepared nanoparticles presented a highly long range chemically ordered core being ferromagnetic at room temperature with a saturation magnetization at room temperature close to the bulk value. After annealing at 750 K the saturation magnetization and the coercive field increase. To investigate the processes involved in the thermal treatment, the temperature dependence of the magnetization and the particle composition, size and structure have been characterized before and after annealing. Besides powder x-ray diffraction (XRD) and x-ray photoelectron spectroscopy (XPS), a detailed study by means of advanced transmission electron microscopy (TEM) techniques has been carried out. In particular, aberration corrected scanning transmission electron microscopy (STEM), has shown that nanoparticles became faceted after the thermal treatment, as a mechanism to reach the thermodynamic equilibrium within the metastable phase. This outstanding feature, not previously reported, leads to an increase of the shape anisotropy, which in turn might be the origin of the observed increase of the coercive field after annealing

High magnetic moment CoFe nanoparticles

International audienc

High Magnetic Moment CoFe Nanoparticles

International audienc