Spin-glass–like ordering in giant magnetoresistive CuCo

The magnetic dynamics in melt-spun Co x Cu 100 − x measured by ac-susceptibilities and magnetic relaxation reveal interaction effects for low Co contents ( x = 2, 10). The frequency dependence of the ac-susceptibility curves vs. temperature described by Néel-Arrhenius relaxation over a distribution of energy barriers yield unphysically small prefactors for the microscopic timescale. The dependence of the peak temperatures on frequency can be described by critical functions with exponents similar to those of conventional spin-glasses. Magnetic relaxation is slow on a logarithmic timescale. The results indicate magnetic interactions resulting in glassy dynamics. Samples of Co 10 Cu 90 with high magnetoresistance ratio show magnetic aging effects in relaxation experiments, which are observed by waiting-time dependences in the time evolution of the magnetization or resistivity after zero-field–cooling. These results are unequivocal evidence for magnetic ordering similar to that in spin-glasses.