Low-temperature spin freezing in soft magnetic nanocrystalline alloys

Abstract Low-temperature spin freezing was observed below 25 K in the nanocrystalline (nc)-Fe92−xZr7BxCu1 (x=2–21 at%) alloys prepared from their amorphous precursors by various heat treatments. The freezing causes magnetic hardening with increasing B concentration and annealing temperature, shown by the temperature dependence of both the susceptibility and coercive field. The phenomenon is attributed to the gradual magnetic blocking of a fraction of nanocrystals decoupled from the ferromagnetic matrix. Similar effects are observed in a Cr-containing FINEMET-type nc alloy.