Superconductors of SmFe1−xCoxAsO synthesized by mechanical alloying

The SmFe1−xCoxAsO (x = 0 − 0.25) superconductors were synthesized by mechanical alloying (MA) and rapid sintering method with Co atoms doped into FeAs layers to replace the Fe sites. The phase purity and superconducting properties of the samples were characterized by X-ray diffraction, electrical resistivity, magnetic susceptibility and Hall coefficient. All the samples belong to the tetragonal ZrCuSiAs structure type with the grain size in 1–3 μm. The superconducting critical temperature Tc of SmFe0.9Co0.1AsO was 12.5 K, and the structure/SDW transition was suppressed by Co doping. The negative Hall coefficient of SmFe0.9Co0.1AsO indicated the electron conduction in the sample. The charge carrier density is about 2 × 1020 cm−3 at the temperature lower than 150 K, larger than that of SmFeAsO.

Research highlights▶ The superconductors of SmFe1−xCoxAsO (x = 0 − 0.25) were synthesized by mechanical alloying (MA) and the rapid sintering. The Co atoms were found more easily to be doped into the FeAs layers of SmFeAsO by this preparation method. The structure transition of the parent SmFeAsO compound was suppressed by Co doping, and the superconductivity of SmFe0.9Co0.1AsO was observed at Tc = 12.5 K. The temperature independent negative Hall coefficient of SmFe0.9Co0.1AsO indicates the electron conduction in the sample. The charge carrier density was about 2 × 1020 cm−3, larger than that of SmFeAsO below 150 K. This confirms that the Co atoms have been doped successfully into SmFeAsO by MA method. ▶ The phase purities and superconducting properties of the samples prepared by MA are similar to the other samples by solid state reactions, but the sample preparing time was shortened to 5 h. This indicates that the mechanical alloying is a rapid and effective method to prepare the LnFeAsO samples by doping Co into the Fe sites of the FeAs layers.