title: Optical-spectroscopic detection of spin-exchange interaction pyrochlore molybdates.
abstract: Optical spectroscopy was used to determine nearest-neighbor spin correlations in pyrochlore molybdates R2Mo2O7 (R=Y, Sm, and Nd), which exhibit ferromagnetic metal to spin-glass insulator transition as the R ion size decreases. Using an analysis based on the orbitally degenerate Hubbard model, we could estimate important physical parameters, such as the effective on-site Coulomb energy U(eff) and the Hund rule exchange coupling J(H). We demonstrated experimentally and theoretically that the effective superexchange interaction between the Mo ions depends on J(H)/U(eff), which determines the phase boundary of the magnetic ground states.
authors.affiliation: ReCOE & School of Physics, Seoul National University, Seoul 151-747, Korea.
authors.forename: M W
authors.initials: MW
authors.lastname: Kim
authors.forename: Y S
authors.initials: YS
authors.lastname: Lee
authors.forename: T W
authors.initials: TW
authors.lastname: Noh
authors.forename: Jaejun
authors.initials: J
authors.lastname: Yu
authors.forename: Y
authors.initials: Y
authors.lastname: Moritomo