Changes in the electronic structure and spin dynamics across the metal-insulator transition inLa1−xSrxCoO3

Abstract

The magnetoelectronic properties of ${\mathrm{La}}_{1\ensuremath{-}x}{\mathrm{Sr}}_{x}{\mathrm{CoO}}_{3}$, which include giant magnetoresistance, are strongly dependent on the level of hole doping. The system evolves, with increasing $x$, from a spin glass insulator to a metallic ferromagnet with a metal-insulator (MI) transition at ${x}_{\text{C}}$ $\ensuremath{\sim}0.18$. Nanoscale phase separation occurs in the insulating phase and persists, to some extent, into the just-metallic phase. The present experiments at 4.2 K have used $^{139}\mathrm{La}$ nuclear magnetic resonance to investigate the transition from hopping dynamics for $x$ $l$ ${x}_{\text{C}}$ to Korringa-like ferromagnetic metal behavior for $x$ $g$ ${x}_{\text{C}}$. A marked decrease in the spin-lattice relaxation rate is found in the vicinity of ${x}_{\text{C}}$ as the MI transition is crossed. This behavior is accounted for in terms of the evolution of the electronic structure and dynamics with cluster size.