epsilon-Fe3-xNixN (0.1 <= x <= 0.8) nanoparticles are investigated for the magnetic interaction effects at low temperatures. The reduction of saturation magnetization (sigma(s)) values is attributed to spin pairing effects and surface spin canting. In ZFC and FC magnetization curves, the surface spin-glass layer (T-f2) and the reentrant spin-glass behavior (T-f2) are evidenced below 27 and 22 K respectively. The surface spin-glass phase is described by the random-field model of exchange anisotropy. Based on this theory, a surface spin-glass layer about 8 nm thick is determined. The reentrant spin-glass behavior occurs due to the disorder created by Ni substitution and is observed for 0.2 <= x <= 0.4. The spin-glass-like ordering in the representative epsilon-Fe2.6Ni0.4N system is verified using spin relaxation dynamics and ac susceptibility measurements. The dynamic scaling analysis, based on imaginary part of the ac susceptibility data, gives the parameters tau(0) = 10(-8) s, T-c = 15.3 K, and zv = 4.5 and hence confirm the spin-glass-like ordering in epsilon-Fe3-xNixN (0.1 <= x <= 0.8) nanoparticles. (c) 2007 Elsevier B.V. All rights reserved.