Tuning Physical Properties via Isovalent Doping in Ba$_{2-x}$Sr$_{x}$CoO$_{4}$

It is known that monoclinic Ba$_{2}$CoO$_{4}$ is an antiferromagnetic (AFM) insulator with Neel temperature $T_{N}$=25K. We found that isovalent Sr substitution for Ba drastically changes the structural and magnetic properties of Ba$_{2-x}$Sr$_{x}$CoO$_{4}$ system. With increasing $x$, $T_{N}$ initially increases then decreases after reaching the maximum at $x$=0.5. Correspondingly, its crystal structure changes from monoclinic ($x<$0.5) to orthorhombic ($x\ge $0.5) at room temperature. The correlation between structure and physical properties will be discussed.