title: Measurement of the giant magnetoresistance effect in cobalt-silver magnetic nanostructures: nanoparticles.
abstract: Cobalt-silver (Co-Ag) core-shell nanoparticles with different silver thicknesses were prepared by the microemulsion method in a two-step reduction process. Transmission electron microscopy (TEM) characterization revealed the almost monodispersity and nanometric size (in the range 3-5 nm depending on the shell thickness) of the synthesized nanoparticles. However, it was the use of high-resolution TEM that revealed the correct core-shell formation of the nanometric material. The selected area electron diffraction pattern indicated the fcc (face-centered cubic) and hcp (hexagonal close packed) nature for silver and cobalt, respectively. Cyclic voltammetry also allowed the correct core-shell formation to be assured. The magnetic properties revealed the presence of both superparamagnetic and ferromagnetic contributions. Because of the lack of methodology, it was necessary to develop a method to measure the magnetotransport properties of the prepared nanoparticles. The strategy which followed was successful as it was possible to measure these properties: giant magnetoresistance values of 0.1% at room temperature were obtained. The numerical analysis of magnetic and magnetoresistance data indicated the presence of superparamagnetic particles showing interaction among the magnetic moments.
authors.affiliation: Electrodep., Physical Chemistry Department and Nanoscience and Nanotechnology Institute (IN2UB) University of Barcelona, Martí i Franquès, 1. E-08028 Barcelona, Spain. garcia.torres.jm@gmail.com
authors.forename: Jose
authors.initials: J
authors.lastname: Garcia-Torres
authors.forename: Elisa
authors.initials: E
authors.lastname: Vallés
authors.forename: Elvira
authors.initials: E
authors.lastname: Gómez