MAGNETORESISTANCE IN FE80-XNIXCR20 (21-LESS-THAN-OR-EQUAL-TO-X-LESS-THAN-OR-EQUAL-TO-30) ALLOYS

Longitudinal and transverse magnetoresistances (MR) and dc magnetization (M) have been measured in Fe80-xNixCr20 (21 less-than-or-equal-to x less-than-or-equal-to 30) alloys where the magnetic phase diagram was already established. The motivation behind the present work is to study the behavior of magnetoresistance (DELTA-rho/rho) in a concentrated alloy system with continuously varying magnetic phases resulting from strongly competitive exchange interactions. We find that all the three samples show negative MR whose magnitude increases with field (as H(n) with n < 1) and decreases with temperature up to 50 K. The MR of the alloy with x = 21 (spin glass), although isotropic like the canonical spin glasses (SG), does not show the usual low-field H-2 dependence but exhibits a correlation with M like DELTA-rho/rho is-proportional-to M2.5. The MR behavior of the x = 23 (mixed phase) alloy is qualitatively similar to that of x = 21 and is like neither a pure SG nor a ferromagnet (FM) showing ferromagnetic anisotropy of resistance (FAR). However, it is rather similar to that of the mixed phase AuFe alloy but with quantitative differences in DELTA-rho/rho vs H and M vs H behaviors. However, Arrott plots (M2 vs H/M) for x = 23 confirm long-range FM order in the mixed phase regime. Similar plots for x = 30 show FM order but the MR shows very small FAR. Large high-field dc susceptibility at 11 K indicates SG ordering for x = 21 and 23. Thus the MR in this system is quite different from those expected of pure magnetic phases.