MAGNETORESISTANCE OF FEXNI80-XCR20(50 LESS-THAN-OR-EQUAL-TO X LESS-THAN-OR-EQUAL-TO 66) AND FE25CR75 ALLOYS

We have measured longitudinal and transverse magnetoresistance (MR) of crystalline pseudo-binary alloys FexNi80-xCr20 (50 less-than-or-equal -to X less-than-or-equal-to 66) and the binary alloy Fe25Cr75. Both th e alloy systems have complex magnetic phases because the alloys have c ompositions close to the critical composition regime for ferromagnetis m. While the Fe-Ni-Cr alloys have a FCC gamma-phase, the binary Fe-Cr alloy has a BCC alpha-phase. This gives an opportunity to compare magn etoresistances for gamma-phase and alpha-phase Fe alloys when they lie close to the critical composition. The experiments were conducted at 4.2 K with magnetic fields up to 7 T. We observed that all the alloys show negative magnetoresistance at 4.2 K in fields up to 7 T. However, for the gamma-phase alloys the typical maximum MR (DELTArho/rho) is a bout 1%, while for the alpha-phase alloy it is 10%. In the gamma-phase alloys there is a small but finite anisotropy Of MR in the phases wit h long-range magnetic order which gradually vanishes near the critical region (x = x(c) congruent-to 59-63) when it becomes a spin glass. In the range x congruent-to x(c), DELTArho/rho is-proportional-to M(n) ( M = magnetization) with n congruent-to 2.