Raman scattering studies of spin, charge, and lattice dynamics in Ca_2-xSr_xRuO₄ (0<~x<0.2)

We use Raman scattering to study spin, charge, and lattice dynamics in various phases of Ca_2-xSr_xRuO₄. With increasing substitution of Ca by Sr in the range 0<~x<0.2, we observe (1) evidence for an increase of the electron-phonon interaction strength, (2) an increased temperature dependence of the two-magnon energy and linewidth in the antiferromagnetic insulating phase, and (3) evidence for charge gap development significantly below the metal-insulator transition (T_MI), and hysteresis associated with the structural phase change, both of which are indicative of a first-order metal-insulator transition and a coexistence of metallic and insulating components for T<T_MI.