Spin dynamics of amorphous Fe_{90- x}Ni_xZr₁₀

Neutron inelastic scattering experiments have been performed in order to study the long wavelength spin dynamics of the amorphous Invar system Fe _90-xNi_xZr₁₀ (for x=5,10). Spin waves were observed over the entire range of wave vectors (0.05-0.15 Å^-1) and temperatures (0.3-0.9 T_C) under study. The spin-wave energies are well described by the quadratic dispersion relation E_q=Dq²+Δ, where Δ is a small gap due primarily to dipolar interactions. The stiffness parameter D renormalizes with temperature as D(T)=D(0) ×[1-A(T/T_C)^{5 /2}] throughout the temperature range under study. The values of D(0) corresponding to x=5, 10, are 42.1 and 78.0 meV Ų, respectively, with A=0.83. In the temperature range 0.55-0.90 T_C the intrinsic spin-wave linewidths Γ_q can be fitted equally well to the q⁴ dependence predicted by hydrodynamic spin-wave theory, or to the q⁵ dependence predicted from the topological disorder in amorphous systems, but they did not show the T ² behavior expected from magnon interactions. These findings suggest that there might be relevant spin-wave broadening mechanisms, perhaps due to the magnetic disorder in the system, in addition to magnon-magnon interactions.