Enhancement of extrinsic magnetoresistance behavior in BiFeO3 doped La0.8Ag0.2MnO3 ceramic

BiFeO3 (BFO) doped La0.8Ag0.2MnO3 ceramics were prepared by the conventional solid-state synthesis method to investigate the effect of BFO on transport and magnetic properties as well as its influence on magnetoresistance (MR). X-ray diffraction analysis showed a decrease in unit cell volume indicating partial substitution of some BFO into the La0.8Ag0.2MnO3 (LaAgMO) lattice while results of scanning electron microscope (SEM) showed improvement in grains connectivity and formation of more regular shaped grains with BFO doping. Energy Dispersive X-ray emission (EDX) analysis showed BFO mainly segregates at the grains boundaries of LaAgMO. Resistivity and susceptibility measurements showed both metal–insulator transition temperatures, TMI and paramagnetic-to-ferromagnetic transition temperature, Tc decreased with increased BFO content indicating weakening of the double exchange, DE mechanism. The temperature dependence of MR showed a small peak around TMI for all samples which is ascribed to the intrinsic MR effect. Below the MR peak, the MR increased almost linearly with decreasing temperature for all samples and this is ascribed to the phenomena of extrinsic MR. The highest MR% (at 40 K) was observed for the x=1.5% sample which showed a MR of more than twice that of the undoped (x=0%) sample. This extrinsic effect is suggested to be related to improved spin polarized tunneling of conduction electrons between grains under external field as a result of improved spin alignment. It is suggested that BFO induced some kind of magnetoelectric coupling between BFO and LaAgMO leading to the enhancement process.