  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.
