Effects of Ru doping on the transport and magnetic properties of aLa1.32Sr1.68Mn2 − yRuyO7 layered manganite system

Abstract

The low temperature magnetization, specific heat, electricalresistance and magnetoresistance have been studied for the Ru-dopedLa1.32Sr1.68Mn2 − yRuyO7 (y = 0.0, 0.04, 0.08 and 0.15) layered manganite system. The undoped compound (y = 0.0) shows a sharpferromagnetic transition (TC) accompanied by a metal–insulator transition (TMI) at 118 K. The Ru substitution decreases theTC andTMI temperatures significantly. The temperature dependence of specific heat measurement confirms the decrease inTC by observing the anomalycorresponding to TC. The decreased effective moments from 3.48 μB for the undopedcompound to 1.82 μB for the highly doped compound at 5 K indicates the Ru substitution weakens theferromagnetic order in the low temperature regime and reduces the number ofMn pairs in the highly doped sample. The field dependence of magnetizationmeasurements exhibits an enhancement of the coercive field with increased Ruconcentration and gives evidence for the mixed magnetic phase for the highly dopedcompound. For the undoped sample, a large negative magnetoresistance of 300% atTC and 128% at 4.2 K in a 5 T field were observed. The magnetoresistance ratio decreasesgradually with increasing Ru substitution. We find that the doped Ru in the Mn site drivesthe layered manganite system towards a magnetically mixed state. The effects of Ru dopingin the transport and magnetic properties will be explained by the antiferromagneticallycoupled Ru and Mn sublattices.