Localized-to-itinerant electron transition in Sr2Ir1−xRuxO4

Abstract

${\mathrm{Sr}}_2$ ${\mathrm{IrO}}_4$ and ${\mathrm{Sr}}_2$ ${\mathrm{RuO}}_4$ are both ${\mathrm{K}}_2$ ${\mathrm{NiF}}_4$-structure oxides. ${\mathrm{Sr}}_2$ ${\mathrm{IrO}}_4$ is a weakly ferromagnetic insulator and ${\mathrm{Sr}}_2$ ${\mathrm{RuO}}_4$ a paramagnetic metal. The ${\mathrm{Sr}}_2$ ${\mathrm{Ir}}_{1\mathrm{-}\mathit{x}}$ ${\mathrm{Ru}}_{\mathit{x}}$ ${\mathrm{O}}_4$ solid solution displays surprising physical properties. On the substitution of Ru to ${\mathrm{Sr}}_2$ ${\mathrm{IrO}}_4$, the Ru first exhibits its expected S=1 local magnetic moment, but at a critical Ru concentration of x≃0.7 the local moment disappears, the apparent density of states at ${\mathit{E}}_{\mathit{F}}$ increases, and an insulator-to-metal transition occurs. These changes in physical properties are accompanied by a change in the crystallographic cell parameters.