Band structures, and magnetic and transport properties of La doped two dimensional Sr_2CoO_4

摘要

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 Sr_(2-x)La_xCoO_4 Structure refinement results reveal that these compounds crystallized in K_2NiF_4-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 Sr_(1.5)La_(0.5)CoO_4 and the results indicate that the system is metallic with a high spin polarization which is responsible for the observed large magnetoresistance.