Mössbauer study of a binary amorphous ferromagnet: ${Fe}_{80}$ $B_{20}$

Binary amorphous ferromagnetic

{Fe}_{80}

B_{20}

has been studied by

{}^{57}{Fe}

Mössbauer spectroscopy from 4.2 to 1050 K. In the amorphous state at temperatures less than the Curie temperature

T_{C} = 685

K, the spectra of

{Fe}_{80}

B_{20}

exhibit well-defined and essentially symmetric hyperfine-field distributions

P (H)

. The analyses of

P (H)

were obtained by deconvoluting the spectra via a Fourier series. The shape of

P (H)

is practically independent of temperature. The values of the effective hyperfine field

H_{eff} (T)

show a temperature dependence of

H_{eff} (0)

(

1 - B T^{\frac{3}{2}} - C T^{\frac{5}{2}} \dots

), indicative of spin-wave excitation. The values of

B = (22 \pm 2) \times 10^{- 6} K^{- \frac{3}{2}}

and

C = (1.4 \pm 0.4) \times 10^{- 8} K^{- \frac{5}{2}}

have been determined. The value of

B_{\frac{3}{2}} = B T_{C}^{\frac{3}{2}} = 0.4 \pm 0.05

is four times larger than those of crystalline Fe and Ni. rf sideband measurements of

{Fe}_{80}

B_{20}

at several frequencies under various field strengths indicate that

{Fe}_{80}

B_{20}

is highly magnetorestrictive with a magnetostriction constant of about 45 ×

10^{- 6}

, which is comparable to the value of 30 ×

10^{- 6}

obtained from static measurements. The amorphous state of

{Fe}_{80}

B_{20}

cannot be preserved near

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Mössbauer study of a binary amorphous ferromagnet:Fe80B20