  We study the structural and magnetic properties of
La$_{0.7}$Sr$_{0.3}$Mn$_{1-x}$Co$_x$O$_3$ ($0 \leq x \leq 1$). Rietveld
refinement of X-ray Diffraction (XRD) pattern suggests phase purity of the
polycrystalline samples with R$\bar{3}$c space group. Interplay of
Ferromagnetic (FM) and Antiferromagnetic (AFM) interaction upon Co substitution
at Mn site in La$_{0.7}$Sr$_{0.3}$MnO$_3$ is evident from magnetic
measurements. There is an optimal cobalt substitution at which the coercive
field is maximum.
