Some Magnetic Properties of Bulk Amorphous Fe–Co–Zr–Hf–Ti–W–B–(Y) Alloys

The microstructure and some magnetic properties of the bulk amorphous (Fe$_{0.61}$Co$_{0.10}$Zr$_{0.025}$Hf$_{0.025}$Ti$_{0.02}$W$_{0.02}$B$_{0.20}$)$_{100-{\rm x}}$Y$_{\rm x}$ (${\rm x} = 0$ or $2$) alloys are studied. The as-quenched and annealed at 720 K for 15-min alloys, well below the crystallization temperature, as confirmed by X-ray diffraction and MÖssbauer spectroscopy studies, are fully amorphous. The investigated alloys are soft magnetic ferromagnets and exhibit relatively high magnetic susceptibility at low magnetic fields. However, the alloys show broad disaccommodation spectra characteristic of amorphous materials. The intensity of disaccommodation distinctly decreases after the addition of 2 at.% of Y to the amorphous Fe $_{61}$Co $_{10}$Zr $_{2.5}$Hf $_{2.5}$Ti $_{2}$W $_{2}$B $_{20}$ alloy and also after annealing at 720 K for 15 min. From the analysis of disaccommodation curves, the average activation energies of elementary processes are estimated. The obtained values of the activation energies, equal to about 1.2 eV, and preexponential factor in Arrhenius law in order of $10^{- 15}$'s indicate that observed disaccommodation phenomenon is connected with the ordering of atom pairs near free volumes. In higher magnetic fields, the magnetization fulfils $M/M_{s}\sim 1/\mu_{0}H$ law, pointing out the presence of quasi-dislocation dipoles with the width lower than the exchange length. After the addition of yttrium to the amorphous Fe$_{61}$Co$_{10}$Zr$_{2.5}$Hf$_{2.5}$Ti$_{2}$W $_{2}$B $_{20}$ alloy and the annealing of the samples at 720 K for 15 min, we observe the decrease of the quasi-dislocation dipoles width.