A Theory for a Self-Trapped Molecular Magnetic Polaron in Ferromagnetic Semiconductor

Abstract

Properties and stability conditions for a self-trapped molecular magnetic polaron in ferromagnetic semiconductors, in which two electrons are trapped in a self-induced localized spin polarization through the strong d-f exchange interaction, are investigated theoretically in particulaly for EuO and EuS numerically. It is shown that the molecular magnetic polaron can be more stable than two single magnetic polarons near Curie temperature if the material has many valley band structures and large dielectric constant. The dependences of the free energy of the molecular polaron as well as the single polaron on the effective electron mass, the Curie temperature and d-f exchange interaction were studied. The possibility of the molecular polaron in EuO and EuS is discussed. Effect of the anisotropic effective mass was also studied by the molecular field theory and was shown that it is not important.