Double metal–insulator peaks and effect of Dy3+ substitution on transport and magnetic properties of hole doped La0·8Ag0·2MnO3

Abstract

The electrical transport and magnetic properties of La0·8−xDyxAg0·2MnO3 (x = 0–0·1) colossal magnetoresistance ceramics have been investigated. All the samples showed transition from metallic behaviour at low temperatures to insulating behaviour at higher temperatures accompanied by ferromagnetic to paramagnetic transition. The Curie temperature Tc decreased from ∼288 K (x = 0) to ∼273 K (x = 0·1) with increasing Dy3+. For x = 0, double metal–insulator transition peaks were observed at Tp1 = 290 K and Tp2 = 261 K. Both peaks and Tc shifted to lower temperatures with increasing Dy3+, indicating that substitution of Dy3+ weakened the double exchange process and enhanced the Jahn–Teller effect. The magnetoresistance peak was observed around Tp1 for all the samples. The electrical behaviour at the metallic region below Tp2 was explained based on electron scattering models, while the Mott variable range hopping model was used to explain the resistivity behaviour above Tp1. The observed double peak behaviour in the ρ(T) curve is suggested to be due to the phase separation induced by inhomogeneity of the samples.