VERY-LOW FIELD AC-RESPONSE AT THE LOSS OF LONG-RANGE MAGNETIC ORDER IN AMORPHOUS FE90ZR10

Low temperature ac-susceptibility measurements over 5 decades of ac-field (0.08-8000 A/m) have been carried out on amorphous ribbons of Fe90Zr10 and Fe91Zr9 We find that at very low fields (0.8 to 24 A/m) ac-response measurements eliminate the influence of domain and domain wall motion, the well known Hopkinson peak effects, to reveal clearly the reentrant characteristics. With such studies a reentrant freezing temperature T(sf) is unambiguously revealed with an evident knee in chi'(T) and a corresponding well defined peak in chi'''(T). The latter is found to be independent of the applied field (0.8 to 8 A/m) while being weakly dependent on the frequency (10 - 1000 Hz). We thus find T(sf) to be 25 K and 40 K respectively for Fe90Zr10 and Fe91Zr9 amorphous ribbons.