HIGH ELECTRICAL-RESISTIVITY BEHAVIOR OF FE-BASED AND CO-BASED SOFT-MAGNETIC HETEROGENEOUS ALLOYS

Following the high electrical resistivity of heterogeneous alloys found recently for high frequency materials useful at 1-500 MHz, the detailed behaviour of the resistivity has been studied in Co80Al20-N, Co80Al20-O and (Co0.0Fe0.1)70B30-O sputtered thin films. The electrical resistivity increases from 10(2) to 10(12) muOMEGA cm with increasing concentration of N (or O), showing an abrupt increase at a critical concentration. The temperature dependence of the resistivity changes significantly with N (or O) content except for CoAl-N alloys. For alloys near the critical concentration a resisitivity minimum appears at a temperature between 30 and 260 K, while the resistivity at lower temperatures follows -log T. In contrast, a tunnelling-type temperature dependence described by exp(T-1/2) is observed for higher N (or O) alloys. It is considered that a weakly conductive network consisting of a heterogeneous mixture of metallic and non-metallic phases, i.e. the percolation of electrical current through this network, governs the resistivity observed.