A Comparative Study of Pulsed Laser And Electron Beam Irradiation Effects In Fe 81 B 13.5 Si 3.5 C 2 Glass
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MONICA SORESCU*, E. T. KNOBBE* AND D. BARB**
*Oklahoma State University, Department of Chemistry, Stillwater, Oklahoma 74078-0447 "**Institute of Atomic Physics, P.O. Box MG/7, R 76900 Bucharest-Magurele, Romania
ABSTRACT
Samples of Fe 8 lB13.5Si 3.5C2 metallic glass were irradiated with a pulsed excimer laser (X=308 nm, T=10 ns), with a high-energy electron beam (W=7 MeV), and with lowenergy electron beams (W=30 and 50 keV). Irradiation-driven changes in the magnetic anisotropy and phase equilibrium of alloy samples were studied by MiSssbauer spectroscopy and scanning electron microscopy. Pulsed-excimer-laser irradiation was found to induce controlled magnetic anisotropy without onset of bulk crystallization in the Fe8 lBl3.5Si3.5C2 amorphous system. High-energy electron-beam irradiation determined an out-of-plane magnetic anisotropy due to changes in the chemical short-range order. Low-energy electronbeam irradiation resulted in the formation of crystalline regions, in which ca-Fe, Fe-Si, Fe 3B, Fe2B, and clusters of y-Fe were identified. Interpretation of these results is given in terms of radiation-enhanced diffusion. INTRODUCTION
In order to understand the relationship between magnetic parameters and structural characteristics of alloy phases, a promising approach involves the study of phase evolution and microstructure development during various irradiation treatments.1 ,2 The present work was carried out in order to investigate the effect of electron-beam irradiation on the magnetic and structural properties of Fe 8 1B 13.5Si 3 .5 C2 amorphous alloy and compare it with the effect of pulsed-excimer-laser irradiation of the same amorphous material. Because of its local-probe
character, Mtssbauer spectroscopy was used to monitor the changes in magnetic anisotropy and phase composition, induced by employing different values of the irradiation parameters in all treatments performed. Related morphological changes were examined by scanning electron microscopy (SEM). Irradiation-driven property changes are discussed in terms of phenomenological models in which the underlying alloy microstructure played an essential role. EXPERIMENTAL
Amorphous alloy Fe8lBl3. 5Si3. 5C2 (Metglas 2605 SC) was supplied by Allied Signal Inc. in the form of 20 gim thick ribbons. The material has a crystallization temperature of 4800C and a magnetostriction constant of 30x10"6 . Square samples (2x2 cm) were cut from the foils and exposed on the shiny side to the X=308 rn radiation generated by a XeCl excimer laser (Lambda Physik), with the pulse width c=10 ns, capable of giving an energy Wp=75 mJ/pulse. A single-pulse energy density of 3 J/cm 2 , corresponding to a laser fluence 4-L=5Xl01 8 photons/cm 2 was achieved by focusing the beam with a cylindrical fused-silica
lens to a spot size of 0.5x5 mm 2. Amorphous samples of Fe 8lBl 3.5Si3.5C2 were irradiated with 2, 5, and 10 laser pulses per spot at a repetition rate of 1 Hz. An acceptable degree of homogeneity was obtained by laser-beam scanning of the sample surface, which was pla
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