Suppression of spin fluctuations by the magnetic field and Co concentration in amorphous Fe_90-xCo_xZr₁₀ alloys

Abstract

Spin fluctuations manifest themselves in the temperature dependence of the spontaneous magnetization M(T,H=0) or the `in-field' magnetization M(T,H), through a contribution that varies with T as [M(T,H) / M(O,H)] = 1-A(H)T²in the intermediate-temperature range and as [M(T,H) / M(O,H)]² = 1-A'(H)T^4/3for temperatures in the vicinity of T_c(Curie point) but still away from criticality. Suppression of spin fluctuations by either the Co concentration in a-Fe_90-xCo_xZr₁₀alloys or the field H for a given composition in the a-Fe_90-xCo_xZr₁₀and a-Fe_90+yZr_10-y alloy series is, for the first time, monitored through the decrease in the coefficients A and A' with increasing x for H = 0 or with H for fixed x or y. While A(0) and A'(0) scale with T_C^-2and T_C^-4/3, respectively, A(H) and A'(H) follow the relation A(H_eff) = A(0)[1-BH^ψ_eff] where A=A or A' ,B = B or B', or ψ = n or n'; and H_eff is the external field corrected for demagnetization. In contrast with the non-monotonic variation in B and n with x, B' varies with x as B'(x)=B'(0)[1-µx^Φ] and n' = 0.50(2) is independent of x in the range ≤ x ≤. The spin fluctuation model explains many of, but not all, these features.