Logarithmic contribution to the electrical resistivity in (Ru1-xIrx)Sr2GdCu2O8 compounds

Abstract

A systematic study of magnetoresistance and dc magnetization was conducted in polycrystalline (Ru1-x Irx) Sr2 GdCu2 O8 [(Ru,Ir)-1212] compounds, for 0≤x≤0.15. We found that a deviation from linearity in the normal-state electrical resistivity (ρ) curves for temperatures below the magnetic transition temperature TM <130 K can be properly described by a logarithmic term. The prefactor C (x,H) of this anomalous lnT contribution to ρ (T) increases linearly with the Ir concentration, and diminishes rapidly with increasing applied magnetic field up to H ≈4 T, merging with the C (0,H) curve at higher magnetic fields. Correlation with magnetic susceptibility measurements supports a scenario of local perturbations in the orientation of Ru moments induced in the neighborhood of the Ir ions, therefore acting as scattering centers. The linear dependence of the prefactor C (x,H=0) and the superconducting transition temperature TSC on x points to a common source for the resistivity anomaly and the reduction in TSC, suggesting that the CuO2 and RuO2 layers are not decoupled.