Spin dynamics of amorphous Fe_90-xNi_xZr₁₀ (invited)

Amorphous Fe_90-xNi_xZr₁₀ is a system that exhibits a relatively high degree of magnetic exchange frustration, which becomes stronger as the system approaches the composition of amorphous pure iron. Thus, while samples with moderate amounts of iron (x≥5) are ferromagnetic, the samples with the highest concentration of iron (x≤1) behave like reentrant spin glasses. We have performed a detailed neutron scattering study of the spin-wave excitations in this system for x=1, 5, 10, 20. In all cases, well-defined spin-wave excitations were observed below a transition temperature T_c that decreased from 455 K (for x=20) to 250 K (for x=1). For x=5, 10, 20 the spin-wave stiffness coefficient follows the temperature dependence expected for a conventional ferromagnet but the spin-wave excitations broaden considerably at low temperatures. For x=1 the spin-wave stiffness coefficient softens at low temperatures and an elastic component of the scattering, associated with the development of a spin-glass order parameter, appears below T≊0.28T_c. A coexistence of propagating spin-wave excitations and spin freezing phenomena is observed below this temperature down to T=0.09T_c. These results are discussed in terms of the relevant current theories.