Influence of rare earth doping on the structural and electro-magnetic properties of SmFeAsO0.7F0.3 iron pnictide

Abstract

The effects of rare earth site doping on the structural, superconducting and magnetic properties of SmFeAsO_0.7F_0.3 iron pnictide are investigated. Gd³⁺ and Ce³⁺ ions are chosen by virtue of their position being on either side of Sm³⁺. Doping of both smaller (Gd³⁺) and larger (Ce³⁺) ions at the Sm³⁺ site increases the T_C up to 55 K. Doping with the smaller Gd³⁺ results in lattice contraction and thereby enhances T_C. It is interesting to observe that though Ce³⁺ doping in SmFeAsO_0.7F_0.3 exhibits an increase in lattice parameters, a substantial enhancement of T_C occurs. The enhancement in T_C due to increased charge carrier concentration is also confirmed using Hall Effect measurement. Apart from T_C enhancement, the simultaneous doping of both at oxygen and rare earth sites prominently increases the superconducting properties such as J_C, H_C1 and H_C2. The co-doped samples also exhibit better magnetic field dependence of J_C over the entire field of study. It is also observed that the Ce³⁺ doped sample shows higher J_C in the high field region due to its enhanced flux pinning properties.