Low-field magnetoresistance in diverse magnetic phases of γ-Fe80−xNixCr20alloys

Abstract

We have measured the low-field (30 G) magnetoresistance (LFMR) in the spin-glass (SG), ferromagnetic (FM), and the reentrant spin-glass (RSG) phases of fcc ${\mathrm{Fe}}_{80\mathrm{\ensuremath{-}}\mathrm{x}}$${\mathrm{Ni}}_{\mathrm{x}}$${\mathrm{Cr}}_{20}$ (19\ensuremath{\leqslant}x\ensuremath{\leqslant}30) alloys. We find close resemblance between the temperature variation of the LFMR and the ac susceptibility in the RSG (x=26). Hysteresis effects in the LFMR have been found in the RSG for both increasing and decreasing temperatures. The presence of a dc biasing field at different temperatures alters the sign of the LFMR in the RSG at the lowest temperatures. This supports the existence of mixed FM and SG phases at the lowest temperature in the RSG. In the SG (x=19), the LFMR becomes negative, while in the FM (x=30), it remains positive. These measurements of LFMR throw new light on our understanding of the various couplings between the moments in such magnetic systems.