  By using a realist microscopic model, we study the electric and magnetic
properties of the interface between a half metallic manganite and an insulator.
We find that the lack of carriers at the interface debilitates the double
exchange mechanism, weakening the ferromagnetic coupling between the Mn ions.
In this situation the ferromagnetic order of the Mn spins near the interface is
unstable against antiferromagnetic CE correlations, and a separation between
ferromagnetic/metallic and antiferromagnetic/insulator phases at the interfaces
can occur. We obtain that the insertion of extra layers of undoped manganite at
the interface introduces extra carriers which reinforce the double exchange
mechanism and suppress antiferromagnetic instabilities.

Materials Science;Strongly Correlated Electrons