FERROMAGNETIC RESONANCE STUDY OF AMORPHOUS AND NANOCRYSTALLINE Fe81B13.5Si3.5C2 RIBBONS

Abstract

The nanocrystallization process in amorphous Fe 81 B 13.5 Si 3.5 C 2 ribbons caused by isothermal annealing below the crystallization temperature is studied. X-ray diffraction and Mossbauer spectroscopy measurements are used to identify the formation of new Fe containing compounds such as the ribbons annealed at various temperatures. The ferromagnetic resonance measurements for an as-cast ribbon and the 495°, 525°C and 600°C annealed ribbons exhibit a resonance line at 63.64 mT for φ = 0°. The sample annealed at 425°C shows two resonance peaks at 95.45 mT and 295.46 mT. These are due to the nanocrystalline α– Fe(Si) phase. The resonance-line widths are seen to broaden after the ribbons are annealed at 495°C and 525°C, at which time, the amorphous matrix crystallizes into nano-grains of α– Fe(Si) , t– Fe 2 B and t– Fe 3 B phases. The kinetics of the crystallization is discussed in terms of the relative change in the line width of the samples annealed at 495°C for different annealing times. These results yielded an Avrami exponent, n of 0.84 which is consistent with diffusion-controlled growth with a nucleation rate close to zero.