influence of nitrogen fractions [N(f)=N(2)/(N(2) + Ar)] and sputtering powers (P(s)) on the structural and magnetic properties of Co-N thin films synthesized by direct current magnetron sputtering have been studied. With increasing N(f) from 0 to 20%, a series of phases from beta-Co, beta-Co (N), Co(4)N to Co(3)N were obtained. However, when N(f) was fixed at 10%, only CO(4)N phase with different Co contents in the films was prepared, whose values of saturation magnetism (M(s)) increased from 12.9 +/- 8.2 Am(2)/kg to 103.9 +/- 6.1 Am(2)/kg with the increase of P(s). Interstitial nitrogen caused the decrease of coercivity from 24.12 kAm(-1) (for beta-Co film) to 2.71 kAm(-1). However, the addition of interstitial nitrogen was not observed to increase the M(s) of beta-Co. (C) 2009 Elsevier B.V. All rights reserved.