Microstructure modification and magnetoresistance enhancement by Ag doping in La2/3Sr1/3MnO3 thin films prepared by dual-beam pulsed laser ablation

The inter-grain extrinsic magnetoresistance (eMR) observed in polycrystalline perovskite manganites has attracted attention recently. Previous efforts aimed at eMR enhancement have concentrated on grain boundary (GB) modification, mainly by insulator doping. In this paper, however, we report our investigations on the doping effect of a metal, Ag, on the eMR phenomenon. La2/3Sr1/3MnO3 (LSMO) thin films were deposited with varying Ag precipitation on (001) LaAlO3 at different substrate temperatures (Ts) by a dual-beam pulsed-laser ablation system. Various analytical techniques were employed to characterize the films. At Ts = 750 ◦C, the films are perfectly epitaxial with their c-axis perpendicular to the film surface. Ag dopant cannot substitute into the LSMO lattice, thus showing no obvious effect on the magneto-transport properties of the film, though it did impair the film in-plane epitaxy and improve the intergrain diffusion of the lattice atoms. However, grown at lower Ts = 400 ◦C, the films are granular with c-axis texture. The Ag dopant exists at GBs and helps to increase the local Mn spin disorder at GBs, thus enhancing the eMR value by a factor of two compared with the undoped film. Experiment data also suggest that the transport mechanism underlying the Ag-doping enhanced eMR is spin-dependent scattering.