Temperature and Pt concentration dependence of exchange bias in PtxCo1 (-) (x)/CoO bilayers are investigated. It is observed that exchange bias properties, blocking temperature and magnetic anisotropy of the PtxCo1 (-) (x)/CoO thin films are strongly affected by the concentration of Pt at the common interface. A detailed structural analysis of antiferromagnetic CoO has been done by x-ray photoelectron spectroscopy (XPS). The XPS data revealed that CoO layer grows with non-stoichiometric behavior which results in other cobalt oxide phases and thus lowers blocking temperature for the exchange biased systems. Increase of Pt concentration in PtCo layer strengthens the exchange bias and thus decreases training of the system. It also results in enhancement of growth-induced uniaxial magnetic anisotropy and onset of exchange bias at higher temperatures. The role of Pt concentration on the interfacial interactions between ferromagnetic and antiferromagnetic layers, and the effect of superstoichiometric CoO on blocking temperature are also discussed. (C) 2013 Elsevier B.V. All rights reserved.