This article presents the results of a study of the plasma characteristics of an electron cyclotron resonance plasma source used for nitriding pure Fe. Diagnostic measurements, using optical emission spectroscopy, Langmuir probes, and an ion analyzer, were recorded as functions of the working pressure (2-8 x 10(-4) Torr) and the external magnetic field near the substrate (from the extremes of highly compressed and divergent plasma fluxes). It was observed that the plasma source is capable of producing high density discharges, about 5 x 10(11) cm(-3) and ion energies about 15-48 eV. The ion energy was highest for the case of a divergent plasma (similar to 45 eV). The most abundant excited radicals produced in the N/H discharges were the NH, N-2 and N-2(+) species. Experiments for nitriding of Fe showed the formation of distinct material structures dependent on the plasma conditions. Conditions were found for which it was possible to form almost single phases of Fe3N and Fe16N2 in the sample surface.