[en] Several techniques such as stereopair diffraction, topo-tomography have been used previously to determine the direction of three-dimensional defects in crystals using monochromic radiation. A new method is proposed here to calculate the orientation of dislocations using white synchrotron radiation, simple and convenient to utilize

[en] In single crystals of Eu_1-xSr_xFe_2-yCo_yAs₂, Co doping suppresses spin-density wave (SDW) ordering and induces a superconducting transition. A resistivity reentrance due to the antiferromagnetic ordering of Eu²⁺ spins is observed, indicating the competition between antiferromagnetism (AFM) and superconductivity (SC). It is striking that the resistivity reentrance can be completely suppressed by a small magnetic field due to a field-induced metamagnetic transition from AFM to ferromagnetism (FM). The resistivity reentrance can also be suppressed by the substitution of Eu²⁺ ions with nonmagnetic Ba²⁺/Sr²⁺ to completely destroy the AFM ordering. These results indicate that the AFM order appears destructive to SC, while FM can coexist with the superconductivity. Further we find that magnon excitation exists in AFM ordering and can be suppressed by an applied field. Coexistence of SC from the FeAs layer and the inner field produced by the ferromagnetic Eu²⁺ layer suggest a possible p-wave component in the superconducting order parameter.