We report on the synthesis, structure and magnetic properties of a novel exchange bias system with Cr2O3/CrO2/Cr2O5 interfaces. Chromium oxide particles with mixed chromium valences were prepared by sintering CrO3 in air. X-ray diffraction patterns show that CrO3 lost its oxygen gradually with increasing temperature and time through Cr3O8, Cr2O5, CrO2, and finally Cr2O3 at temperatures above 760 K. X-ray photoelectron spectra indicate a low CrO2 content and a binding energy of 579.3 eV for Cr 2p(3/2) photoelectrons in Cr2O5. Chromium dioxide was found to stably coexist with Cr2O3 and Cr2O5 in the particles. Magnetic measurements show hysteresis loop shifts in the sample, indicating an exchange bias induced by antiferromagnetic Cr2O3/Cr2O5 in ferromagnetic CrO2. An exchange bias of 9 mT at 5 K and a coercivity of 26.3 mT were observed in the chromium oxide particles containing CrO2. (C) 2011 Elsevier B.V. All rights reserved.