We investigated the effects of annealing on LaMnO 3 epitaxial thin films grown by pulsed laser deposition and propose an efficient method of characterizing their stoichiometry. Structural, magnetic, and optical properties coherently indicate non-stoichiometric ferromagnetic and semiconducting phases for as-grown LaMnO 3 films. By annealing in an oxygen-reducing atmosphere, we recovered the antiferromagnetic and insulating phases of bulk-like stoichiometric LaMnO 3 . We show that non-destructive optical spectroscopy at room temperature is one of the most convenient tools for identifying the phases of LaMnO 3 films. Our results serve as a prerequisite in studying LaMnO 3 based heterostructures grown by pulsed laser deposition.

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We investigated the magnetic and optical properties of [(LaMnO 3 ) n /(SrTiO 3 ) 8 ] 20 (n = 1, 2, and 8) superlattices grown by pulsed laser deposition. We found a weak ferromagnetic and semiconducting state developed in all superlattices. An analysis of the optical conductivity showed that the LaMnO 3 layers in the superlattices were slightly doped. The amount of doping was almost identical regardless of the LaMnO 3 layer thickness up to eight unit cells, suggesting that the effect is not limited to the interface. On the other hand, the magnetic ordering became less stable as the LaMnO 3 layer thickness decreased, probably due to a dimensional effect.

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