CRITICAL SLOWING DOWN OF THE SPIN RELAXATION IN NANOCLUSTERED FE-AL-B ALLOYS

A vast number of heterogeneous magnetic systems, which are the subject of present scientific and technological attention, display disordered magnetic arrangements as a result of spatial and/or anisotropy randomness and competition between interactions of different sign. The magnetic relaxation of atomic spins (or the macrospin of nanoparticles) slows down upon cooling and, under certain conditions, finally collectively freeze in a spatially uncorrelated magnetic configuration, called the spin-glass (or superspin-glass) state [1-4]. The superspin freezing temperature will depend on the particle size and concentration, and also on the matrix nature [2]. The terms superspin-glass (SSG), or superferromagnet, were coined analogously to the older term superparamagnetism: the prefix “super ” expresses the substitution of the atomic spin by a particle magnetic moment of several hundreds/thousands Bohr magnetons, with the particle ensembles retaining, nonetheless, the essential magnetic behavior of the corresponding atomic-spin scenario (paramagnetism, ferromagnetism, or spin-glass), only with higher transition temperatures from the collective low temperature states to the superparamagnetic regime [4]. These terms have been applied in relatively different solids such as ultrafine monodispersed Fe-C particles [5] and Co80Fe20/Al2O3 discontinuou