Oblique irradiation using a gas cluster ion beam (GCIB) has been studied in order to achieve low-damage smoothing of magnetic materials. We investigated how the surface morphology and surface roughness depended on the angle of incidence. Quite smooth surfaces could be obtained using both normal and grazing-incidence irradiation. At incident angles larger than 45?, periodic ripples were formed. The orientation of the ripples changed from perpendicular to parallel with respect to the GCIB when the incident angle exceeded a critical value. Surface roughening resulting from the formation of ripples was observed at incident angles between 45° and 65°. Fluctuations in the Ni/Fe component ratio and the intermixing of oxygen from the native oxide were evaluated. As the angle of incidence increased, both the thickness of the layer in which the component ratio was fluctuating and the depth of oxygen intermixing decreased. As a result, it was determined that low-damage smoothing of magnetic materials could be performed by using grazing-incidence irradiation from a GCIB.