Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO$_{1-x}$F$_x$ ($x =$ 0.05, 0.1, 0.2, 0.25, and 0.3)*

Anisotropic structural and magnetic properties of the field-aligned superconducting system SmFeAsO$_{1-x}$F$_x$ ($x =$ 0.05, 0.1, 0.2, 0.25, 0.3) are reported. Due to the Fe spin-orbital related anisotropic exchange coupling, all the tetragonal microcrystalline powders in epoxy were aligned at room temperature using the field-rotation method where the tetragonal $ab$-plane is parallel to the magnetic alignment field $B_a$ of 0.9 T and the $c$-axis parallels to the rotating axis. Anisotropic magnetic properties are studied through low temperature magnetic measurements along the $c$-axis and paralleled to the $ab$-plane of aligned samples in both ZFC and FC modes. The under-doped compound ($x =$ 0.1) is not superconducting with an antiferromagnetic N\'{e}el temperature $T_N \sim$ 40K, while the two optimum-doped compounds ($x =$ 0.2 and 0.25) show high superconducting transition temperatures $T_c$ of 49K and 50K, respectively. The variation of anisotropic structural and magnetic properties for this system are discussed and compared with the previously reported 52 K anisotropic superconductor Sm$_{0.95}$La$_{0.05}$FeAsO$_{0.85}$F$_{0.15}$.