Ferromagnetic tendencies at the surface of AF/CO bulk manganites*

Previous investigations have shown that the surface of a ferromagnetic (FM) manganite has antiferromagnetic (AFM) tendencies. However, the development of ferromagnetism has been observed experimentally in some AFM charge-ordered (CO) manganites by reducing the grain size down to the nanoscale. Similar phenomenon was also found in other nanosized CO oxides, such as La$_{1/3}$Sr$_{2/3}$FeO$_{3}$. To clarify these puzzling observations, using Monte Carlo techniques we studied the FM Kondo model, using open boundary conditions to simulate a surface. For some values of the couplings, the previously known tendency to an AFM outer shell was found for the case of a bulk FM state. But for other couplings, the opposite effect was observed: the existence of a FM layer at the surface of a AFM/CO material. Details will be provided in this presentation.