Microstructure dependent magnetotransport properties in polycrystalline La0.7Sr0.3MnO3 ultrathin films on thermally oxidized Si substrates

•LSMO ultrathin films were deposited on Si/SiO2 by two-step growth method using PLD.•AFM revealed decreasing grain size and RMS roughness with lowering film thickness (t).•Metallic resistivity nature of LSMO films retained even in ultrathin range (~10 nm).•Resistance minima and low field MR enhanced with decreasing t, at low temperatures.•Low field MR enhanced due to intergranular Spin Polarized Tunnelling.