NANOSTRUCTURE OF GIANT MAGNETORESISTANCE HETEROGENEOUS ALLOYS NI0.20AG0.80 AFTER ANNEALING

Heterogeneous alloys Ni0.20Ag0.80, presenting giant magnetoresistance properties, have been studied by Total Electron Yield X-ray absorption spectroscopy at liquid nitrogen temperature at the Ni K edge from as- deposited to annealed stages. Up to 150 degrees C annealing, the Ni at oms are mainly in small poorly ordered agglomerates and the local Ni a tomic environment is very stable and disordered. Up to 250 degrees C a nnealing, some Ni atoms occupy substitutional sites in the Ag matrix a nd 40 to 50 % of the Ni nearest neighbors are Ag atoms. After annealin g at 400 degrees C during 10 mn, the nanostructures evolve towards lar ger, more compact and well ordered granules. The Ni-Ni distance varies from 0.246 to 0.248 nm as the annealing temperature increases indicat ing that the small agglomerates are under strain in the Ag matrix.