Electrical transport properties of Mn-doped LaFeAsO oxypnictide

We report on the electrical transport properties of the Mn-doped LaFe1-xMnxAsO oxypnictide system. We show that the substitution of iron by manganese in the FeAs layer leads to a gradual expansion of the lattice parameters and of the Fe-As and Fe-Fe bond lengths, as well as a change in the angles of the FeAs4 tetrahedron which becomes more regular. The structural transition from tetragonal to orthorhombic coupled to the emergence of a spin density wave is rapidly suppressed by Mn doping. Interestingly, Mn doping does not lead to p-type behaviour. Moreover, no superconducting transition is observed, and the system evidences a metal-semiconductor transition around x = 0.03. Thus, there is apparently no symmetric behaviour of the manganese doping and cobalt doping in the FeAs layer of the LaFeAsO system. (C) 2009 Elsevier B.V. All rights reserved.