Manganese oxide nanoparticles were prepared in an inert gas condensation system. X-ray Diffraction (XRD) studies revealed presence of multiple manganese oxide phases while high resolution transmission electron microscopy (HRTEM) showed polycrystalline hollow nanoparticle morphology. The additional inner surface of the hollow nanoparticle directly affect the magnetic properties of these particles. Combined physical structure, electronic structure and magnetic susceptibility analyses led to the conclusion that the prepared nanoparticles are polycrystalline and composed of gamma-Mn2O3 and MnO crystallites. Magnetic study found a sharp peak around 38 K with no frequency dependence in the AC susceptibility measurement. Large coercivity (H-C) and exchange bias (H-EB) fields, up to 11 kOe and 7 kOe, respectively, were observed below the order temperatures. H-C and H-EB were found to increase and decrease, respectively, as a function of cooling field. Both He and HEB were found to decrease monotonically as the temperature approached paramagnetic phase transition of the ferrimagnetic component. (C) 2016 Elsevier B.V. All rights reserved.