In an attempt to identify the driving force for the formation of chains composed of nanometer size Fe alloy particles that were recently reported, experiments have been carried out with the magnetic metals Fe, Co, and Ni and a nonmagnetic metal Cu. The samples obtained by a reduction of aqueous metal chloride solutions with potassium borohydride have been characterized by x-ray diffraction, transmission electron microscopy, and superconducting quantum interference device magnetometer measurements. The results reveal that the magnetic interaction between the adjacent particles plays a determining role in the chain structure formation. Although both crystallinity and boron content do not play a direct role, they influence significantly the magnetic properties, and thereby have an indirect role in the formation of the chain structures. ©1997 American Institute of Physics.