Preparation of nanocrystalline Ag-ME (ME = Co, Fe and Ni) materials by gas flow condensation technique

Heterogeneous Ag-ME (ME = Fe, Co, Ni) nanostructured alloys have been prepared by a new process utilizing co-evaporation of the metals in a continuous gas flow. Inert gas, at different final pressures, has been injected into a ultra-high vacuum chamber through a nozzle in order to establish a convectional flow that carried nanocrystallites of the ME over an evaporation source of Ag, so that part of the atoms of silver condensed at the surface of the ME crystallites as thin coating. The average grain size of the Ag-ME powders, determined both by X-ray diffraction and surface area analysis, increased with the He pressure (pHe). Electrical measurements revealed a decrease of the resistivity of the compacted Ag-ME samples in a magnetic field; values of the giant magnetoresistance effect as large as 26% (ME = Co, pHe = 100 Pa), 8% (ME = Fe, pHe = 1000 Pa) and 7% (ME = Ni, pHe = 800 Pa) have been observed, at room temperature and a magnetic field H = 1.5 T.