Structure, transport and magnetic properties in La2xSr2−2xCo2xRu2−2xO6

The perovskite solid solutions of the type La$_2x$Sr$_2-2x$Co$_2x$Ru$_2-2x$O$₆$ with 0.25 $\leq$ x $ \leq $ 0.75 have been investigated for their structural, magnetic and transport properties. All the compounds crystallize in double perovskite structure. The magnetization measurements indicate a complex magnetic ground state with strong competition between ferromagnetic and antiferromagnetic interactions. Resistivity of the compounds is in confirmation with hopping conduction behaviour though differences are noted especially for $x$ = 0.4 and 0.6. Most importantly, low field (50Oe) magnetization measurements display negative magnetization during the zero field cooled cycle. X-ray photoelectron spectroscopy measurements indicate presence of Co$²⁺$/Co$³⁺$ and Ru$⁴⁺$/Ru$⁵⁺$ redox couples in all compositions except $x$ = 0.5. Presence of magnetic ions like Ru$⁴⁺$ and Co$³⁺$ gives rise to additional ferromagnetic (Ru-rich) and antiferromagnetic sublattices and also explains the observed negative magnetization.