Band structures, and magnetic and transport properties of La doped two dimensional Sr2Co04

In this work, we report on our studies on the band structure calculations, structures, transport, and magnetic properties in two dimensional layer structured perovskite compounds Sr2−xLaxCoO4. Structure refinement results reveal that these compounds crystallized in K2NiF4-type structures with space group I4/mmm. The temperature dependence of resistivity shows a semiconductorlike behavior over a wide range of temperatures, a metal-insulator transition at 240 K, and an upturn at 160 K for the x = 1, 1.25, and 0.75 samples. A coercive field is about 1 T for the sample with x = 0.75, while it is about 0.05 T for x = 0.75 and 0.1 T for the x = 1.25 samples. A negative field hysteresis magnetoresistance in close correlation with the coercive field has been observed and can be explained by the grain boundary tunneling effect. The first-principles band structure calculations were carried out for Sr1.5La0.5CoO4 and the results indicate that the system is metallic with a high spin polarization which is responsible for the observed large magnetoresistance.