부산대학교 도서관

The phase diagram of half-doped manganites which may consist of experimentally observed ferromagnetic (FM), A-,C-, and charge-exchange (CE)-type antiferromagnetic (AF) states is obtained in terms of a model which is based on double exchange via degenerate e{sub g} orbitals, the on-site Coulomb interaction (U), and the nearest-neighbor Coulomb interaction (V). We find that, because of the strong spatial anisotropy of the electron hoppings, the on-site Coulomb interaction has different effects on these magnetic order states. As a result, large values of U suppress the FM state and favor the A- and C-type AF states. Moreover, we show that it is the interplay between the on-site and nearest-neighbor Coulomb repulsions that stabilizes the CE phase and results in the charge ordering in the state.