Spin Dynamics in the Amorphous Invar Alloy of Fe₈₆B₁₄

抄録

The spin waves in an amorphous Invar alloy Fe₈₆B₁₄¹¹, have been studied by inelastic neutron scattering. Well defined magnon groups were detected around (0, 0, 0) up to q=0.12 Å⁻¹ for various temperatures below T≤0.9 T_c. The spin waves show the dispersions hω_q(T)=E₀(T)+D(T)q² with D(T) varying with temperature according to D(T)=D(0)(1−aT^5⁄2) with D(0)=118±6 (meVA²). The spin wave stiffness at 0 K, D(0), thus determined is almost twice as large as the value D_M(0)=68±2 (meVA²) determined for the same sample by a magnetization measurement. The spin wave linewidth Γ varies with wave vector q as Γ=aq² and it shows only limited temperature dependence. All of these features are quite similar to those found in the crystalline Invar alloys as Fe₆₅Ni₃₅ and Fe₃Pt.