Structural, electronic and magnetic properties of 3d transition metal doped strontium clusters are studied using first-principles electronic structure methods based on density functional theory. Clusters with enhanced kinetic and thermodynamic stability are identified by studying their hardness, second order energy difference and adiabatic spin excitation energy. CrSr 9 and MnSr 10 are found to have enhanced stability. They retain their structural identities in assemblies, and are classified as magnetic superatoms. A qualitative understanding of the magnetic coupling between two cluster units is arrived at. Reactivity of these superatoms with O 2 molecule is also studied. Prospects for using these magnetic superatoms in applications are discussed.