Giant magnetoresistance in granular CuFeNi alloys

Giant magnetoresistance (MR) was studied in alloys of composition Cu80Fe10N i10, Cu80Fe15Ni5, Cu80Fe5Ni15, and Cu80Fe20, produced by melt spinning and annealed in the temperature range 300-600 degrees C. Materials were charact erized by Mossbauer spectroscopy at several temperatures. At both 78 and 30 0 K, spectra for all CuFeNi compositions showed a singlet associated with s uperparamagnetic Fe nanoparticles, but at 4.2 K the sextet characteristic o f ferromagnetic Fe was visible. From the hyperfine field reduction we estim ated the radius of the Fe particles. Magnetization data for Cu80Fe10Ni10 at 300 K were compared with a model which features a log-normal distribution of noninteracting superparamagnetic particles. Thus the mean magnetic momen t and the particle density were determined. The magnetoresistance ratio MR was compared to a model which considers bulk and interface scattering. (C) 1998 American Institute of Physics. [S0021-8979(98)26311-0].