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

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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 ∼6.5% at 300 K in a field of 9 T. The MR decreases to ∼2.5% as the annealing temperature increases to 500 °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 °C, which shows MR characteristics that are different from the as-cast and 300 °C annealed microwires.