Magnetic aftereffect spectroscopy of Fe- and Co-based amorphous alloys

Abstract

Theoretical and experimental fundamentals of a computer-based spectroscopic method--magnetic aftereffect (MAE) spectroscopy---giving sets of elementary activation energy (AE) spectra of magnetic relaxation (MR) processes, are introduced. Structural MRs in two representative amorphous alloys, ${\mathrm{Fe}}_{75}{\mathrm{Si}}_{15}{\mathrm{B}}_{10}$ and ${\mathrm{Co}}_{70}{\mathrm{Fe}}_{5}{\mathrm{Si}}_{15}{\mathrm{B}}_{10}$, were investigated by MAE spectroscopy. The MAE measurements were performed on the as-cast and annealed samples in a temperature range of $77--620\phantom{\rule{0.3em}{0ex}}\mathrm{K}$. Activation parameters of the individual directional reordering processes were obtained. The B- and Si-type MRs were identified in the FeSiB and CoFeSiB alloys. The B-type MRs originate from the reorientation of Co-B or Fe-B atom pairs. The Si-type MRs come from the reorientation of Co-Si or Fe-Si pairs. Atom pairs Fe-B, Co-B, Fe-Si, and Co-Si are aligned by the increasing values of the most probable activation energies (AE) of the MR. For the B and Si types of the MR, the two most probable activation energies, ${Q}^{*}=1.33$ and $1.55\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$, with the pre-exponential factors ${\ensuremath{\tau}}_{0}=2\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}15}$ and $6\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$, respectively, were obtained in the as-cast FeSiB alloy. For the as-cast ${\mathrm{Co}}_{70}{\mathrm{Fe}}_{5}{\mathrm{Si}}_{15}{\mathrm{B}}_{10}$ alloy, the B and Si types of the MR are characterized by the activation energies ${Q}^{*}=1.38$ and $2.16\phantom{\rule{0.3em}{0ex}}\mathrm{eV}$ and the pre-exponential factors ${\ensuremath{\tau}}_{0}=8\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}16}$ and $9\ifmmode\times\else\texttimes\fi{}{10}^{\ensuremath{-}18}\phantom{\rule{0.3em}{0ex}}\mathrm{s}$, respectively. Low temperature annealing causes lowering of the MAE peaks and shifts the peak temperatures and the AEs of MRs in both alloys to higher values. The MAE and AE spectra of the annealed CoFeSiB amorphous alloy exhibit one peak only.