Magnetotransport and micro-x-ray absorption near-edge structure studies of glass-coated Fe-Ni-Cu microwires

Magnetotransport and micro-x-ray absorption near-edge structure (micro-XANES) studies of glass-coated 20Fe-20Ni-60Cu microwires have been carried out on both as-cast and heat-treated samples. The micro-XANES spectroscopy data were collected at the K edges of Cu, Ni, and Fe with the x-ray microprobe beamline at the Center for Advanced Microstructures and Devices. Comparison of the Fe K-edge spectra from the microwires to standard spectra reveals that the Fe atoms in the as-cast sample are in a face-centered cubic (fcc) configuration and they remain in the fcc phase throughout the annealing processes. Giant magnetoresistance (GMR) has been observed in the microwires and it reaches similar to 6.5% at 300 K in a field of 9 T. The MR decreases to similar to 2.5% as the annealing temperature increases to 500 degrees C. The loss of GMR upon annealing is attributed to the growth of Fe-Ni rich magnetic particles. Significant reduction in the number of extremely small particles is obtained after annealing at 500 degrees C, which shows MR characteristics that are different from the as-cast and 300 degrees C annealed microwires. (C) 2000 American Institute of Physics. [S0021-8979(00)57708-1].