Spin dynamics of amorphous Fe_90−xNi_xZr₁₀

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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+, where 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 _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 T² 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. Journal of Applied Physics is copyrighted by The American Institute of Physics.