Electrical transport and magnetic properties of La4/3Sr5/3Mn2O7

The structure, electrical and magnetic transport properties of polycrystalline La4/3Sr5/3Mn2O7 synthesized by a sol-gel method were studied. The X-ray diffraction (XRD) shows that the obtained sample forms with Sr3Ti2O7-type perovskite structure. The resistivity versus temperature ((rho)-T) curve shows that the insulator-metal transition occurs at ~120 K, coincident with the three-dimension (3D) ferromagnetic (FM) ordering temperature observed in the measurement of magnetization and ac magnetic susceptibility (Xac). Except the insulator-metal transition at ~120 K, there is another insulator-metal transition below 120 K and the feature is especially obvious in a field of 5 T. As a circumstantial evidence, the (rho)-T curves in zero field and a field of 5 T of the Ca- or Ba-doped sample is measured and there is only one insulator-metal transition in both cases. The results can be explained by that the Ca- or Ba-doped sample is purer than La4/3Sr5/3Mn2O7.