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 compos ed of nanosized solid solution grains embedded in an amorphous matrix of ro ughly the same composition. The irreversibility between the field-cooled an d zero-field-cooled magnetization curves together with some ac susceptibili ty features closely resemble those exhibited by spin glasses. However, the analysis of the nonlinear susceptibility allowed us to rule out the existen ce of a true thermodynamic phase transition, since it was apparent the abse nce of a divergent increase in the nonlinear coefficients on approaching th e freezing temperature. Surface effects are considered a minor source for t he observed phenomena, remaining the blocking of interacting superparamagne tic moments the main mechanism to account for them. We discuss these three different origins for spin-glass-like behavior in the context of mechanical ly alloyed materials. [S0163-1829(99)04041-2].