Influence of the Fe Concentration on the Superconducting Properties of Fe $$_{1-y}$$ 1 - y Se

Abstract

We present a comparative study of electrical transport properties in the normal state and in the dissipative superconducting state between pure \(\beta \)-FeSe phase and Fe deficient Fe\(_{1-y}\)Se crystals. We discuss the influence of the intergrowth of the magnetic hexagonal phase (Fe\(_7\)Se\(_8\)) in Fe deficient samples when compared to pure \(\beta \)-FeSe samples. In the superconducting state, we measured the \(ab\)-plane electrical resistivity with magnetic field up to 16 T and the electrical resistivity as a function of the angle between the \(c\) axis and the applied field. The angular dependence at fixed temperature below the superconducting critical temperature, \(T_c(H=0)\), is very different for both sets of crystals. The Fe deficient samples display a vortex pinning-related feature at \(\sim \)57\(^\circ \) off the plane while the pure \(\beta \)-FeSe phase samples show the persistence of a strong angular-dependent magnetoresistance characteristic of the normal state electronic structure.