Growth, annealing effects on superconducting and magnetic properties, and anisotropy of FeSe_1-xTe_x (0.5 ≤ × ≤ 1) single crystals

Single crystals of FeSe_1-xTe_x (0.5 ≤ × ≤ 1) have been grown by the Bridgman method. After annealing them at 400 °C for 100h in vacuum, single crystals of × = 0.5-0.9 have exhibited bulk superconductivity. Anisotropic properties of the electrical resistivity and upper critical field, H_c2, have been investigated for the single-crystal FeSe_1-xTe_x with × = 0.6. It has been found that the in-plane resistivity, ρ_ab, shows a metallic temperature-dependence, while the out-of-plane resistivity, ρ_c, shows a broad maximum around 100 K. The resistivity ratio, ρ_c/ ρ_ab, is 44 and 70 at 290 K and just above the superconducting transition temperature, T_c, respectively. The anisotropic parameter, γ = H^∥_c2/H_c2 (superscripts ∥ and indicate field directions parallel and perpendicular to the ab-plane, respectively.), is estimated as 2.7 just below T_c.