We have prepared iron nanowire arrays on stepped W(110) substrates by step-flow growth at elevated temperatures. The correlation between structural, electronic and magnetic properties of the iron nanowires was probed by spinpolarized scanning tunneling microscopy and spectroscopy in ultra-high vacuum, at low temperatures and in external magnetic fields. We found a strong dependence of the nanomagnetic domain structure on the width of the double-layer iron nanowires as well as atomic-scale domain walls in the single-layer nanowires. Both observations point towards unique properties of low-dimensional magnetic systems which are not observed in the bulk material. (C) 2002 Elsevier Science B.V. All rights reserved.