(Fe81Co19)N thin films were prepared by reactive radio frequency magnetron sputtering in an argon and nitrogen mixture atmosphere. The as-deposited (Fe81Co19)N thin films have a high saturation magnetization (mu Ms-0) of up to similar to 2.36 T and good soft magnetic properties. The grain size and magnetoelastic effects strongly affect the soft magnetic properties of the (Fe81Co19)N thin films due to the introduction of nitrogen into Fe(Co) lattice. The high frequency characteristics of the (Fe81Co19)N thin films were examined in 0.1 to 7 GHz frequency range using a shorted microstrip transmission-line perturbation method. The (Fe81Co19)N thin films with lower nitrogen contents exhibit a high permeability over 400 at low frequency and a high resonance frequency of up to 2.8 GHz. The thin films with higher nitrogen contents have stripe domain structures and yield distinct multiple-peak permeability spectra. (c) 2008 Elsevier B.V All rights reserved.