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Cr(N)-beta-Cr2N nanoparticles were prepared by arc-discharge process in a mixture of argon, hydrogen and nitrogen gases. The nanoparticles are composed of the two components, i,e. Cr(N) solid-solution nanoparticles (polyhedral shape) and beta-Cr2N nitrogen-deficiency nanoparticles (cuboidal shape). Both the nanoparticles share a similar shell-core structure: the shell consists of chromium oxide Cr-2(CrO4)(3) or Cr-O (20 at% Cr), and the complex of Cr and N-O, as well as the core of Cr(N) solid-solution or beta-Cr2N. Moreover, the nanoparticles have a blocking temperature of 29 K and a narrow size distribution. The weak ferromagnetism can be interpreted in terms of the presence of non-compensated surface spins. For the field-cooled (FC) magnetization with the field of 0.01 T, a perfect Curie-Weiss fit of the data above 50 K indicates paramagnetic characteristics of the nanoparticles. This is supported by the hysteresis loops at 5 and 295 K. The paramagnetic Curie temperature of -124 K suggests the type of dominant interaction is antiferromagnetic. (c) 2006 Published by Elsevier B.V.