Localized-to-itinerant electron transition in Sr2Ir1-xRuxO4

Sr2IrO4 and Sr2RuO4 are both K2NiF4-structure oxides. Sr2IrO4 is a weakly ferromagnetic insulator and Sr2RuO4 a paramagnetic metal. The Sr2Ir1-xRuxO4 solid solution displays surprising physical properties. On the substitution of Ru to Sr2IrO4, the Ru first exhibits its expected S=1 local magnetic moment, but at a critical Ru concentration of x0.7 the local moment disappears, the apparent density of states at EF increases, and an insulator-to-metal transition occurs. These changes in physical properties are accompanied by a change in the crystallographic cell parameters.