Influence of grain size on magnetic and transport properties of polycrystalline La0.8Sr0.2MnO3 manganites

In this study, we have investigated the effects of grain size on the magnetic and transport properties of polycrystalline La0.8Sr0.2MnO3 samples. The samples were prepared by solid-state reaction method. In order to obtain a series of samples with different grain sizes, the bulk sample was subjected to high energy ball milling. The magnetization decreases by decreasing grain size. A decrease in magnetization by decreasing grain size is due to the increasing of magnetically disordered states at the surface of grains. By decreasing the grain size the resistivity increases and a second peak was observed at temperatures well bellow Tc. The intrinsic CMR decreases by decreasing grain size while the extrinsic intergranular MR is promoted to larger values. A model, proposed by Zhang et al. [N. Zhang, W. Ding, W. Zhong, D. Xing, Y. Du, Phys. Rev. B 56 (1997) p. 8138.], involving domain walls contribution and a spin polarized tunneling between neighboring grains of manganites below transition temperature may be responsible for this behavior.