Positron Annihilation Studies in the Sm_2/3Sr_1/3MnO_3+δ

We measured lifetime and doppler broadening spectra of Sm_2/3Sr_1/3MnO_3+δ as functions of temperature by positron annihilation technology In terms of lifetime spectrum, we found that the lattice effects triggered by ferromagnetic transition give rise to the change of the coefficient of the average linear thermal expansion of Sm_2/3Sr_1/3MnO_3+δ at T_c. In terms of doppler broadening spectrum, we found the delocalization of low-momentum electrons occurs in Sm_2/3Sr_1/3MnO_3+δ at metal-insulator transition temperature.