Anisotropic characteristics and critical behaviors in Mn doped K0.8Fe2Se2 single crystal

We report the anisotropic superconducting properties of nominal K0.8Fe1.97Mn0.03Se2 single crystal. The phase separation is characterized by X-ray diffraction and scanning electron microscopy techniques. The experimental crystal has three superconducting transitions at T-c1(mag) = 31.9 K for the first, T-c2(mag) = 36.8 K for second, T-c3(mag) = 42.5 K for third superconducting phase as seen from magnetic susceptibility measurements. We can discriminate the anisotropic upper critical fields between the second and third superconducting phase by magnetotransport measurements. The upper critical field at T = 0 K are estimated to be mu H-0(c2)parallel to ab (0) = 137.4 T and mu H-0(c2)parallel to c (0) = 51.8 T for the second, mu H-0(c2)parallel to ab (0) = 178.4 T and mu H-0(c2)parallel to c (0) = 52.6 T for third superconducting phase, respectively. We also discuss the vortex pinning in framework of thermally activated flux flow model, by which the pinning potential U-0 of the second superconducting phase is derived to be U-0(parallel to c) = 5.1 x 10(3) K and U-0(parallel to ab) = 6.1 x 10(3) K at mu H-0 = 0.25 T, respectively. Finally, we will evaluate the total critical current density, which shows moderate values J(c)(0) similar to 10(3) - 10(4) A/cm(2) at T = 3 K. (C) 2014 Elsevier B.V. All rights reserved.