Low temperature magnetization and magnetoresistance studies on the layered manganite system La1.2Sr1.8Mn2−xRuxO7 (x=0, 0.1, 0.5, 1.0)

We report the detailed results of magnetization and magnetoresistance measurements in the Ru doped layered manganite system La1.2Sr1.8Mn2−xRuxO7 (x=0, 0.1, 0.5, 1.0). High-resolution measurements of magnetization and magnetoresistance were carried out as functions of temperature, magnetic field and time. We find evidence for the existence of competing ferromagnetic and antiferromagnetic interactions resulting in the formation of a frustrated spin-glass-like state at low temperatures. The time dependent magnetization follows the relation M = M 0 − M 1 log ( t ) very well. We find that Ru doping enhances the coercive field and drives the system towards a magnetically mixed phase at low temperatures. Large negative magnetoresistance values are observed in all samples and at low temperatures the magnetoresistance varies as the square root of the applied magnetic field.