We report nano-scale mechanical heterogeneity of a metallic glass characterized by dynamic force microscopy. Apparent energy dissipation with the variation of ~12%, originating from non-uniform distribution of local viscoelasticity, was characterized.The correlation length of heterogeneous viscoelasticity was measured to be ~2.5±0.3 nm, which is well consistent with the dimension of shear transformation zones for plastic flow. This study provides the first experimental observation on the nano-scale mechanical heterogeneity in a metallic glass, and may fill the gap between atomic models and the macroscopic properties of metallic glasses.
The magnetization reversal process in microfabricated FePt (0 0 1) dots with a diameter of 250 nm is experimentally investigated based on phenomenological analysis. The initial and minor magnetization curves show that the magnetization reversal of the FePt dots is dominated by the nucleation of reversed domains. The phenomenological analysis of the coercivity (Hc) gives the defect regions for nucleation as 26 ± 4 nm and 18 ± 6 nm for the FePt dots before and after annealing, respectively. The reduction of the defect regions after annealing is in agreement with the enhancement of Hc for the annealed dots. Micromagnetic simulations also show the reduction of Hc due to the existence of defects in a dot, which is consistent with the experimental results.
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