Mössbauer study of a binary amorphous ferromagnet:Fe80B20

Binary amorphous ferromagnetic ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$ has been studied by ${}_{}{}^{57}{}_{}{}^{}\mathrm{Fe}$ Mössbauer spectroscopy from 4.2 to 1050 K. In the amorphous state at temperatures less than the Curie temperature $T_C=685\mathrm{}$ K, the spectra of ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$ exhibit well-defined and essentially symmetric hyperfine-field distributions $P\left(H\right)\mathrm{}$. The analyses of $P\left(H\right)\mathrm{}$ were obtained by deconvoluting the spectra via a Fourier series. The shape of $P\left(H\right)\mathrm{}$ is practically independent of temperature. The values of the effective hyperfine field $H_{\mathrm{eff}}\mathrm{}\left(T\right)\mathrm{}$ show a temperature dependence of $H_{\mathrm{eff}}\mathrm{}\left(0\right)\mathrm{}$ ($1-B{T}^{\frac{3}{2}}-C{T}^{\frac{5}{2}}\cdots$), indicative of spin-wave excitation. The values of $B=(22\mathrm{}\pm 2)\times {10}^{-6\mathrm{}} {\mathrm{K}}^{-\frac{3}{2}}$ and $C=(1.4\mathrm{}\pm 0.4)\times {10}^{-8\mathrm{}} {\mathrm{K}}^{-\frac{5}{2}}$ have been determined. The value of $B_{\frac{3}{2}}=B{T}_C^{\frac{3}{2}}=0.4\mathrm{}\pm 0.05$ is four times larger than those of crystalline Fe and Ni. rf sideband measurements of ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$ at several frequencies under various field strengths indicate that ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$ is highly magnetorestrictive with a magnetostriction constant of about 45 × ${10}^{-6\mathrm{}}$, which is comparable to the value of 30 × ${10}^{-6\mathrm{}}$ obtained from static measurements. The amorphous state of ${\mathrm{Fe}}_{80}$ ${\mathrm{B}}_{20}$ cannot be preserved near