Magnetic properties of spin diluted iron pnictides from μSR and NMR in LaFe1-xRuxAsO

The effect of isoelectronic substitutions on the microscopic properties of LaFe1-xRuxAsO, for 0 <= x <= 0.8, has been investigated by means of mu SR and La-139 NMR. It was found that Ru substitution causes a progressive reduction of the Neel temperature (T-N) and of the magnetic order parameter without leading to the onset of superconductivity. The temperature dependence of La-139 nuclear spin-lattice relaxation rate 1/T-1 can be suitably described within a two-band model. One band giving rise to the metallic antiferromagnetic ground state, while the other one is characterized by weakly correlated electrons. Ru for Fe substitution yields a progressive decrease of the density of states at the Fermi level close to the one derived from band structure calculations. The reduction of T-N with increasing Ru content follows the predictions of the J(1)-J(2) model on a square lattice, which appears to be an effective framework to describe the magnetic properties of the magnetic ground state.