INDUCED ANISOTROPY AND PHASE-TRANSFORMATION IN METALLIC GLASSES BY PULSED-EXCIMER-LASER IRRADIATION

Ferromagnetic amorphous ribbons (Metglas 2605 CO, Metglas 2605 SM, Metglas 2826 MB, and Metglas 2605-S3A) were exposed isochronally to pulsed-excimer-laser irradiation (lambda = 308 nm, tau = 26 ns) by employing various repetition rates and pulse energies. The effects of laser treatment were studied by transmission Mossbauer spectroscopy and scanning electron microscopy. Complementary information was obtained using conversion electron Mossbauer spectroscopy and energy-dispersive x-ray analysis. At moderate values of the repetition rate and pulse energy, controlled magnetic anisotropy could be induced in the higher magnetostriction samples without the onset of crystallization. similarly, a random distribution of magnetic-moment directions was obtained in the lower magnetostriction samples. The laser-induced changes in the magnetic anisotropy were correlated to the presence of molten zones subsequently quenched and of correspondingly induced mechanical stresses. Analysis of the magnetic texture of the irradiated surfaces supported the model of closure domain structure. At higher values of the repetition rate and pulse energy, the nature of the observed phase transformation could be elucidated by a combination of complementary methods. The effect of excimer-laser-induced crystallization in metallic glasses was evidenced and explained considering characteristics of high-fluence laser irradiation. Through a suitable selection of irradiation parameters, the effects of induced anisotropy and partial crystallization can be used following the laser treatment proposed for tailoring the magnetic properties of metallic glasses with regard to specific applications.