Undoped cages of (ZnO)n nanoclusters are magic with n = 12 and 34. However with Mn doping, our ab initio calculations show that O rich, nonstoichiometric Zn12MnO15 and Zn34MnO 37 nanoclusters obtained from n = 13 and 35, become magic with 1μB magnetic moment. The Mn-doped nanoclusters can also be viewed as composite structures where a MnOx species (x = 1-4) is attached to (ZnO)n (n = 12 and 34) cages. Mn atoms can exist in a high oxidation state in these nanoclusters, with the highest binding energy for x = 3. Further replacement of Mn by Cr leads to a neutral, nonmagnetic Zn12CrO 15 nanocluster with a large highest occupied molecular orbital and lowest unoccupied molecular orbital gap of 2.24 eV. These results provide new ground to understand doped nanostructures of ZnO and may also shed light on magnetism in Mn-doped ZnO thin films. © 2012 American Physical Society.