Hopping conduction and logarithmic divergence in transport of Ru-1222 ruthenocuprates

The possibility of the hopping conduction in the normal state of ruthenocuprate superconductor Ru₁Sr₂Gd_1.5Ce_0.5Cu₂O₁₀ (Ru-1222) has been studied. In the framework of the variable range hopping (VRH) model it is impossible to explain the resistive behavior in the entire range of temperature. In one group of differently annealed Ru-1222 samples the logarithmic contribution has been extracted and studied. A deviation from the hopping conduction behavior has been explained by considering the logarithmic contribution in several Ru-1222 with metallic normal state observed in limited range of temperature. In another group of Ru₁Sr₂Gd_1.4Ce_0.6Cu₂O_y (Ru-1222) samples with different oxygen contents VRH has been observed in absence of the logarithmic divergence. Possibility of the charge localization and impact of the local magnetic moment (LMM) have been discussed to explain the upturn in resistive behavior