Suppression of spin fluctuations by the magnetic field and Co concentration in amorphous Fe90-xCoxZr10 alloys

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(0, H)]=1-A(H)T2 in the intermediate-temperature range and as [M(T, H)/M(0, H)]2 =1-A'(H)T4/3 for temperatures in the vicinity of Tc (Curie point) but still away from criticality. Suppression of spin fluctuations by either the Co concentration in a-Fe90-xCoxZr10 alloys or the field H for a given composition in the a-Fe90-xCoxZr10 and a-Fe90+yZr10-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 TC-2 and TC-4/3, respectively, A(H) and A'(H) follow the relation Α(Heff)=Α(0)[1-ΒHeffψ] where Α=A or A', Β=B or B', ψ=n or n' and Heff 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-μxφ] and n'=0.50(2) is independent of x in the range ≤x≤6. The spin fluctuation model explains many of, but not all, these features. (author)