Mössbauer study of the superspin glass transition in nanogranularAl49Fe30Cu21

Abstract

The spin-glass-like behavior observed in mechanically alloyed ${\mathrm{Al}}_{49}{\mathrm{Fe}}_{30}{\mathrm{Cu}}_{21}$ is attributed to the collective freezing of ferromagnetic nanoclusters, i.e., the appearance of a superspin glass phase. The presence of the clusters and their estimated size $(\ensuremath{\sim}1 \mathrm{nm})$ were inferred from magnetization measurements. The transition critical exponent $z\ensuremath{\nu}=13.8\ifmmode\pm\else\textpm\fi{}0.4,$ extracted from ac-susceptibility data, is similar to those obtained in other superspin glasses. M\ossbauer spectroscopy offered more direct evidence: the component related to the clusters undergoes a transition from a high-temperature quadrupolar doublet to a distribution of sextets, whose mean hyperfine splitting grows with decreasing temperature in a similar fashion to spin glasses. The relation between these magnetic dynamics and the sample structure is addressed.