Anomalous hall effect of calcium-doped lanthanum cobaltite films

The Hall resistivity, magnetoresistance, and magnetization of La1−xCaxCoO3 epitaxial films with 0.25⩾x⩾0.4 grown on lanthanum aluminate were measured in fields up to 7 T. The x=1/3 film shows a reentrant metal insulator transition. Below 100 K, the x=1/3 and 0.4 films have significant coercivity which increases with decreasing temperature. At low temperature the Hall resistivity remains large and essentially field independent in these films, except for a sign change at the coercive field that is more abrupt than the switching of the magnetization. A unique magnetoresistance behavior accompanies this effect. These results are discussed in terms of a percolation picture and the mixed spin state model for this system. We propose that the low-temperature Hall effect is caused by spin-polarized carriers scattering off of orbital disorder in the spin-ordered clusters.