HIGH-TEMPERATURE RESISTIVITY MINIMA IN CO-RICH AMORPHOUS FERROMAGNETS

High-resolution electrical-resistivity data have been obtained for the cobalt-rich amorphous ferromagnets Fe5Co50Ni(17-x)Cr(x)B16Si12 (x = 0, 5, 10, and 15) and Fe5Co50Mn17B16Si12 between 8 and 300 K. The resistance minimum, which is congruent-to 15 K for x = 0, shifts to temperatures congruent-to 200 K and above on substitution by Cr or Mn. In a sample with x = 0, in the region above T(min), there is clear evidence of a magnetic term propotional-to T2 in addition to the structural term. A quantitative analysis, based on electron-electron interaction and localization effects, is reported here for ferromagnetic systems exhibiting resistance minima at high temperatures. We find for T < T(min) (x > 0), three distinct regions where the conductivity varies as square-root T, T, and square-root T at low, intermediate, and high temperatures, respectively, in agreement with the predictions of existing theories. The magnetic scattering seems to contribute very little below T(min).