The Laser-Mössbauer Method for Surface Evolution and Thin Film Microstructure

Abstract

ABSTRACTUsing amorphous Fe81B13.5Si3.5C2, Fe40Ni38Mo4B18, Fe66Co18B15Si1 and Fe72.6Cr22Al4.8Si0.3Y0.3 as model systems, we apply the laser-Mössbauer method in order to obtain metallic glasses with novel properties. As shown by transmission Mössbauer spectroscopy, the bulk magnetic texture was modified in a rational manner by applying a varying number of excimer laser pulses per spot (λ=248 nm, τ=8 ns). As shown by conversion electron Mössbauer spectroscopy, this process left the surface magnetic texture unchanged and induced a distribution of magnetic moment directions throughout the thickness of the foil. A similar dependence of the magnetic texture upon the number of applied laser pulses was obtained in metallic glasses irradiated with a Nd:YAG laser (λ=532 nm, τ=8 ns). However, in this case we observed the onset of surface crystallization in the hyperfine magnetic field distributions extracted from the CEMS spectra. When a pulsed alexandrite laser was used (λ=750 nm, τ=60 μs), the onset of crystallization was found to be accompanied by bulk oxidation and the formation of magnetite particles in the irradiated system. Finally, a crucial experiment was performed in order to demonstrate the role played by the magnetostriction constant in the onset of crystallization.