Superconducting, magnetic and magnetotransport properties of FeTe1-xSex single crystals

Abstract

The single crystalline samples with compositions FeTe1-xSex (0.25 ≤ x ≤ 0.50) have been prepared via self-flux method and the superconducting, magnetic and magnetotransport properties of the grown crystals were investigated. The superconducting onset temperatures have been determined from the measurements of zero field cooled magnetization and resistance with temperatures. In the present case, highest superconducting transition temperature TC (onset) ∼ 15 K has been obtained for x=0.5. The HC2 (T=0 K) values have been estimated by fitting the experimental HC2 - T plots with WHH model. The highest HC2(0) has been obtained for x=0.5. The activation energy of the thermally activated flux flow has been found from the broadening of superconducting transition in an applied magnetic field using the Arrhenius law. Our results show that the activation energy (U0) decreases with the increasing magnetic field. Furthermore, the magnetization measurements for x=0.4 and 0.5 samples have been performed at T=5 K in the magnetic field range ±7 T to estimate critical current density at different applied magnetic fields using Bean formula. We see that the sample x=0.5 has higher values of JC as compared to that of x=0.4 at all magnetic fields. This is in conformity with the behavior of U0–H plots.

Evolution of Superconducting Properties in Fe1.1Se0.8Te0.2 Films Before and After Structure Avalanche

“…It can be seen that, for films with t > 55 nm, all of them have rather close activation values and field dependencies. At low fields, U reaches as high as 5000 K, which is much larger than that of the optimally doped FeSeTe bulk single crystal (∼10 2 K) and other different kinds of superconductors, such as BaFe 1.9 Co 0.1 As 2 (2.9 × 10 3 K), LaOFFeAs (1 × 10 3 K), and Bi-2122 (∼900 K) . This suggests rather strong pinning of Fe 1.1 Se 0.8 Te 0.2 films.…”