Nonequilibrium magnetic dynamics in mechanically alloyed materials

The magnetically glassy behavior of mechanically alloyed ${\mathrm{Fe}}_{61}{\mathrm{Re}}_{30}{\mathrm{Cr}}_9$ is reported in detail, including a static and dynamic study of the freezing process, the observation of aging in a mechanically alloyed sample, Mössbauer analysis, and annealing experiments. Despite the clear collective character of the low-temperature change of regime, no thermodynamical spin-glass mean-field transition could be proved. On the other hand, the careful comparison of the magnetic behavior with that reported in strongly interacting fine particles systems hinted towards the presence of that kind of particles in our samples. Structural considerations based on XRD, Mössbauer, and the evolution of the ac susceptibility peaks upon annealing pointed to the existence of very fine Fe-rich clusters able to support a magnetic moment, confirming the diagnosis extracted from the magnetic dynamics analysis. The argument is strengthened by the study of the effects of milling on the freezing temperature in a second sample showing a similar behavior: ${\mathrm{Fe}}_{35}{\mathrm{Al}}_{50}{\mathrm{B}}_{15}.$ The explanation can be extended naturally to previously reported mechanically alloyed, spin-glass-like samples, which hints towards the generalization of our interpretation.