Very low field AC-response at the loss of long range magnetic order in amorphous Fe90Zr10

Low temperature AC-susceptibility measurements over five decades of AC field (0.08-8000 A/m) are carried out on amorphous ribbons of Fe ₉₀Zr₁₀ and Fe₉₁Zr₉. It is found that at very low fields (0.8 to 24 A/m), AC response measurements eliminate the influence of domain and domain wall motion to reveal clearly the reentrant characteristics. With such studies, a reentrant freezing temperature T_sf is unambiguously revealed with an evident knee in χ\´(T) and a corresponding well defined peak in χ"(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). T_sf is found to be 25 K and 40 K, respectively, for Fe ₉₀Zr₁₀ and Fe₉₁Zr₉ amorphous ribbons