THE EFFECT OF NITROGENATION ON GMR AND MICROSTRUCTURES OF GRANULAR (NI0.8FE0.2)(20)AG-80 THIN-FILMS

The effect of nitrogenation on the giant magnetoresistance (GMR) and m icrostructure of (Ni0.8Fe0.2)(20)Ag-80 thin films prepared by d.c. rea ctive magnetron sputtering has been investigated on a superconducting quantum interference device (SQUID) at 4.2 K and at room temperature. Also, the phase constitution and microstructure of these thin films ha ve been studied via transmission electron microscopy (TEM), X-ray diff raction (XRD) and X-ray photoelectron spectroscopy (XPS). The magnetor esistance (MR) ratio of (Ni0.8Fe0.2)(20)Ag-80 was found to be 25% at 4 .2 K and 5.4% at room temperature. When nitrogen was introduced during sputtering and keeping the other processing parameters the same, the change in the MR ratio of such prepared specimens was one half of the pure counterpart at room temperature. However, the saturation field wa s markedly lowered from 5 T to about I T and at the same time the diff erential sensitivity improved markedly. The MR ratio became larger wit h increasing annealing temperature. XPS results show that the core ele ctron levels of Ag 3d(3/2), Ag 3d(5/2) and Ni 2p(3/2) of the nitrogena ted specimens shift to slightly higher energy levels on nitrogenation. At the same time, an additional shoulder on the satellite Ni 2P(3/2) peak shows up around 861 eV. Such XPS observations indicate nitride fo rmation during sputtering under nitrogen atmosphere. The nitrides and microstructural changes seem to have caused the GMR and saturation fie ld to change. (C) 1998 Acta Metallurgica Inc.