Local structure investigation of Co-Fe-Si-B ribbons by extended X-ray absorption fine-structure spectroscopy

In the present work, extended X-ray absorption fine-structure (EXAFS) investigations of Co₆₉Fe_xSi_21-xB₁₀ (x = 3, 5, 7) glassy ribbons were performed at the Co K-edge. The magnitude of the first peak of the Fourier transforms of the EXAFS signals is found to increase monotonically with increasing Si concentrations indicating the formation of the localized ordered structure at the atomic scale. The Co-Si coordination number (CN) increases at the expense of the CN of Co/Fe. Smaller interatomic distances are observed in the glassy phase compared with that in the crystalline phase which promotes the stability of the glassy phase. Calculations of the thermodynamic parameter (P_HSS), cohesive energy (E_C) and the atomic radius difference (δ) parameter show that the alloy composition Co₆₉Fe₃Si₁₈B₁₀ has a good glass-forming ability (GFA) with the highest CN of Si compared with other compositions. A linear correlation of CN with that of the GFA parameter (P_HSS) exists and the CN also plays a crucial role in the GFA of the glassy alloys. This parameter should be considered in developing different GFA criteria.

Temperature and impurity effect on parallel field magnetoconductance of bulk insulating topological insulator (Bi1-x Sb x )2Te3

We have performed a systematic parallel field magnetotransport studies of (Bi_1-x Sb _x )₂Te₃ to understand the temperature and impurity effect on the interference of bulk conductance on the surface states of highly insulating topologically insulating compound Bi₂Te₃. The compound exhibits a weak antilocalization effect (WAL) at low temperature and low magnetic field. WAL weakens and a weak localization effect is observed to be developed in the compound with the increase in temperature due to the creation of topologically trivial 2D electron gas states. Strong interlayer interference and coupling of bulk carriers with surface states are observed at low temperature. A similar temperature effect is observed for all concentrations of Sb. Topologically protected surface states enhance with the increase in Sb contents up to x  =  0.3; however, a further increase in Sb concentration leads to a decrease in surface states. The data has been analysed via the generalised Altshuler and Aronov model for parallel field transport anticipating weak antilocalization and interlayer interference.