Characterization of phases in nanocrystallized metglass 2826 Mb by coincident doppler broadening (CDB) spectroscopy technique

The iron and cobalt based magnetic materials with nanocrystalline phase having size less than 50 nm distributed in the amorphous matrix have shown great improvement in their soft magnetic properties in comparison to fully amorphous material. The characterization of microstructure of these nanocrystallized material is essential for obtaining best soft magnetic properties In recent times, it has been shown that Positron annihilation technique has potential to characterize the nano-particles in a amorphous matrix. Momentum of electron in electron-positron pair causes a Doppler broadening in energy of annihilated γ-ray. Positron annihilation with valence electron and core electrons are reflected in low momentum and high momentum regions of momentum distribution respectively. By analyzing these low and high momentum regions information regarding the size and chemical environment respectively of the trapping sites can be obtained. In the present work, CDB spectra of amorphous and nanocrystallized Metglass 2826 MB alloy were obtained. The CDB spectra were also obtained for pure constituting elements Fe, Ni, Mo and B of the alloy. CDB spectra were also simulated to compare the experimental observations. The examinations of these spectra along with X-ray diffraction (XRD) and Transmission electron microscopy (TEM) studies have shown that positron has strong tendency for annihilation in secondary cubic boride phase. These observations were found to be consistent with positron life time measurement study. (author)