The magnetic ordering in epsilon-Fe3N nanoparticles can be controlled by simultaneous variation of the particle size and nitrogen stoichiometry, which can lead to the ferromagnetism at room temperature. In this study, similar to 73 nm epsilon-Fe3-yN1+y (0.1 <= y <= 0.2) particles with saturation magnetization of 129.0 emu/g at 5 K (close to bulk 133.0 emu/g) are compared to similar to 20 nm epsilon-Fe2.999N1.001 particles. X-ray photoelectron spectroscopy (XPS) studies indicate the formation of nanometric surface oxide/oxynitride layer on the ferromagnetic/superparamagnetic nitride core. The nanoparticles are highly interacting with strong dipolar and exchange interactions. AC-susceptibility measurements confirm the spin-glass-like ordering at lower temperatures. (C) 2010 Elsevier B.V. All rights reserved.