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Directional ordering in the amorphous Co75Si15B10 alloys by means of the magnetic after-effect (MAE) of the initial reluctivity and its influence on the Perminvar effect have been investigated. Two peak MAE spectra were obtained from isochronal measurements for as-cast as well as annealed samples. The spectrum of the as-cast sample has peak maxima at 383 and 545 K. Comparing this MAE spectrum with the spectrum of amorphous Co75B25 alloy, we identified the first peak as a result of Co–B atom pair reorientation (B-type relaxation) and the second one at higher temperatures as a result of Co–Si atom pair reorientation (Si-type relaxation). After annealing, the peaks shift to 442 and 576 K, respectively. For the numerical analysis of Co75Si15B10 MAE spectra we modified the micromagnetic model assuming the existence of more relaxation processes, where each process is connected to the relaxation of one metalloid element. The pre-exponential factor for B-type relaxation was found to be τ0,AC(B) = 7 × 10−17 s with the most probable activation energy QAC*(B) = 1.31 eV. These values correlate very well with the magnetic relaxation (MR) activation parameters of Co75B25 alloy, τ0,AC = 2 × 10−17 s and QAC* = 1.35 eV. Si-type relaxation has activation parameters τ0,AC(Si) = 6 × 10−18 s and QAC*(Si) = 1.96 eV. After annealing the sample at 683 K for 30 min they change to values τ0,AN(B) = 2 × 10−15 s, QAN*(B) = 1.38 eV and τ0,AN(Si) = 3 × 10−17 s, QAN*(Si) = 2.01 eV. The complicated shapes of the long-time isotherms reflect the superposition of two relaxation processes. We have numerically split each isotherm into two sub-isotherms representing the particular contributions of the two relaxation processes. The MAE spectrum of the critical field measured on the as-cast sample also has two peaks, like the reluctivity spectrum. The impact of Co–B and Co–Si atom pairs on the behaviour of the domain wall stabilization potential is discussed for the explanation of the observed MR results.

The kinetics of the structural magnetic relaxations (MRs) in the Co-based amorphous alloys has been investigated by magnetic after-effect spectroscopy. The experimental evidence and characterization of two types of MRs in the amorphous Co 75 B 25 and Co 75 Si 15 B 10 alloys are rendered in this work. The binary CoB alloy shows only the B-type MR with the most probable energy of the activation energy spectrum Q * = 1.35 eV and the preexponential factor 0 =2ϫ 10 −17 s. In the ternary CoSiB amorphous alloy, the additional Si-type MR with Q * = 1.96 eV and 0 =6ϫ 10 −18 s occurs. Low-temperature annealing shifts either of the relaxation parameters of both alloys to higher values. Roles of the free volumes, the dimension, and affinity of the B and Si atoms for Co in the MR are discussed.The structural magnetic relaxation significantly influences the magnetic properties, processibility, and stability of the amorphous alloys. The Co-based amorphous alloys play an important role in technical applications because of their excellent soft magnetic properties. 1,2 They exhibit good processibility by the magnetic annealing, 3 which the atomic mechanism lies in the magnetic relaxion (MR). A powerful tool for investigating the MR is magnetic after-effect (MAE) spectroscopy. 4 There are two theoretical approaches to MAE in the amorphous alloys. The micromagnetic model of the MR 5 is based on the reorientations of the atom-pair axes near free volumes to the directions related to the local magnetizations (Fig. 1). A driving force for the reorientation is a reduction of the interaction energy of a given atom pair with the local magnetizationwhere 1 and 2 denote the initial and final angles between the atom-pair axis and the local magnetization, 0 is the local interaction energy consisting from exchange ͑ ex ͒, spin-orbit ͑ K ͒, and magnetoelastic ͑ ex ͒ parts, 0 = ex + K + el . Each atom pair acts as an individual two-level system. Assuming the first-order reaction, the time-temperature dependence of the reluctivity influenced by the MR can be expressed by the equation 6where r 0 ͑T͒ is reluctivity at t =0, ⌬r ϳ n 0 is the maximum reluctivity change (n 0 -concentration of mobile atom pairs), p͑͒ is the distribution function of relaxation times , 0 is the preexponential factor, Q is the activation energy, k is the Boltzmann's constant, 00 is a constant of the order of 10 −13 s related to Debye frequency, and S is the activation entropy.By the magnetostrictive model, 7 the magnetostriction of alloy contributes to the MAE level and the MAE appears as independent of the actual alloy composition. The possible role played by the compositions of the amorphous and nanocrystalline alloys in the MRs is not definitely clarified. 8,9 It looks to be reasonable to start an investigation of the MR in Co-based amorphous alloys with a binary CoB alloy. 10 The only composition of the CoB-based amorphous alloy in which the atom-scale mechanism of the MAE was suggested is the hydrogen-charged Co 75 Si 15 B 10 . 11 At 190 K, a hydrogen-related relaxatio...

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