Superconductivity at 14 K in SmFe0.9Co0.1AsO

We report superconductivity in the SmFe_0.9Co_0.1AsO system being prepared by most easy and versatile single-step solid-state reaction route. The parent compound SmFeAsO is non-superconducting but shows the spin density wave (SDW) like antiferromagnetic ordering at around 140 K. To destroy the antiferromagnetic ordering and to induce the superconductivity in the parent system, the Fe²⁺ is partially substituted by Co³⁺. Superconductivity appears in SmFe_0.9Co_0.1AsO system at around 14 K. The Co doping suppresses the SDW anomaly in the parent compound and induces the superconductivity. Magnetization measurements show clearly the onset of superconductivity with T _c^dia at 14 K. The isothermal magnetization measurements exhibit the lower critical fields (H _c1) to be around 200 Oe at 2 K. The bulk superconductivity of the studied SmFe_0.9Co_0.1AsO sample is further established by open diamagnetic M(H) loops at 2 and 5 K. Normal-state (above T _c) linear isothermal magnetization M(H) plots excluded the presence of any ordered magnetic impurity in the studied compound.      

NMR Study on (CH 3 ) 2 NH 2 H 2 AsO 4

Proton NMR line width and spin-lattice relaxation time T 1 for the ferroelectric (CH 3 ) 2 NH 2 H 2 AsO 4 have been measured at the temperature range between 77 K and 300 K. The temperature dependence of T 1 is well described by the expressions based on rotation of the methyl group using the value of activation energy E a = 99 meV and elementary correlation time τ0 = 1.5 ×10 -13 sec. Moreover, a sharp dip of T 1 near ferrroelectric phase transition temperature ( T c = 274.5 K) results from the ordering of protons. In addition, the temperature dependence of T 1 deviates from the expression for molecular rotation above around 200 K. It is deduced that the deviation is caused by the suppression of some kind of proton motion.