The effect of high magnetic field on the microstructure and magnetic properties of α′-FeN films has been studied. The application of a high magnetic field during sputter deposition has a significant influence on the microstructure of α′-FeN films. In particular, the grain growth and the surface roughness are suppressed, and concurrently the coercivity becomes much lower. α′-FeN films deposited in magnetic fields of 2 and 4 T exhibit smooth surfaces with root-mean-square (rms) roughness of, respectively, 0.38–1.53 nm, saturation magnetization of 2.25–2.32 T and coercivity of 1.6–2.6 kA/m, while α′-FeN films deposited at H=0 T show rough surfaces with rms roughness of 6.0–6.8 nm, saturation magnetization of 2.13–2.15 T and coercivity of 9.8–12 kA/m. This effect of high magnetic field on the surface morphology is expected to be widely used to improve various properties of thin films. © 2003 American Institute of Physics.