Magnetic phase transition in two-phase multiferroics predicted from first principles

On the basis of first-principles electronic-structure calculations we predict that epitaxial multiferroic films-fabricated as ultrathin Fe films deposited on TiO2-terminated (001) surfaces of ATiO(3) perovskites (A=Pb,Ba)-exhibit an unexpected change in their magnetic structure with increasing Fe-film thickness. The magnetic order changes from ferromagnetic, with a magnetization of about 3 mu(B)/atom for the 1 ML system, to ferrimagnetic with almost vanishing magnetization upon deposition of a second Fe layer. Ferromagnetic order is restored for thicker Fe films but with significantly reduced magnetization as compared to Fe bulk. The effect is understood in terms of hybridization of electronic states and geometric structure. The magnetoelectric coupling affects the size of the magnetic moments moderately; a spin-reorientation transition is not found.