A filtered cathodic vacuum arc technique has been applied to synthesis iron-nitride thin films on silicon (100) substrate. Two approaches were carried out to introduce the nitrogen gas into the chamber to control the nitrogen content. Films with smooth surface containing alpha-Fe(N), alpha'-Fe(N), alpha"-Fe16N2, gamma'-Fe4N, zeta-FeA epsilon-Fe3N and gamma"-FeN phases have been obtained, respectively. The magnetic properties of the films show that small amount of nitrogen addition into the iron films increases the saturation magnetization, while excess nitrogen decreases the saturation magnetization. It is explained based on the bond-band-barrier correlation mechanism [C.Q. Sun, Prog. Mater. Sci. 48 (2003) 52 1] that the electronegative nitrogen changes the valence states of iron into Fe+ or Fe dipoles with higher magnetic momentum compared with an neutral Fe atom in the bulk. (c) 2004 Elsevier B.V. All rights reserved.