Spin waves in amorphous Fe1−xBx alloys

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Abstract
The temperature dependence of spin excitations has been studied in amorphous Fe1−xBx (x = 0.18 and 0.14) by inelastic neutron scattering. The spin‐wave stiffness constant D was determined directly from the magnon dispersion curves (E = Dq2) over the temperature range from below room temperature (T/TC = 0.48 and 0.36, respectively, for x = 0.18 and 0.14 alloys) up to 548 K (T/TC = 0.75 and 0.99), which is just below the crystallization temperature. For both alloys the temperature dependence of D was found to be proportional to (T/TC)5/2 up to (T/TC) greater than 0.8. The extrapolated values of D at T = 0 were D = 167 and 138 meV A2, respectively, and were nearly twice as large as those determined from the T3/2 coefficient found from magnetization studies. These anomalies may be related to the Invar characteristics of the thermal expansion in these alloys. Limited data were also obtained for an alloy Fe76B24 which exhibits a higher D (≳174 meV A2).

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