Spin-glass-like behavior in mechanically alloyed nanocrystalline Fe-Al-Cu

We report on the magnetic properties of mechanically alloyed Al₄₉Fe₃₀Cu₂₁. The system was observed by high-resolution electron microscopy to be composed of nanosized solid solution grains embedded in an amorphous matrix of roughly the same composition. The irreversibility between the field-cooled and zero-field-cooled magnetization curves together with some ac susceptibility features closely resemble those exhibited by spin glasses. However, the analysis of the nonlinear susceptibility allowed us to rule out the existence of a true thermodynamic phase transition, since it was apparent the absence of a divergent increase in the nonlinear coefficients on approaching the freezing temperature. Surface effects are considered a minor source for the observed phenomena, remaining the blocking of interacting superparamagnetic moments the main mechanism to account for them. We discuss these three different origins for spin-glass-like behavior in the context of mechanically alloyed materials.