The magnetic properties of Fe-Co alloys used as catalysts for vertically aligned carbon nanofiber growth are presented at several stages in the formation process: from thin films to dewetted islands to carbon-encapsulated particles. Electron microscopy shows their morphological properties as a function of the alloy ratio. The magnetic properties are investigated by superconducting quantum interference device magnetometry in a field range of vertical bar H vertical bar <= 20 kOe and temperatures between 2 and 330 K. Magnetization measurements illustrate a composition dependence of the magnetic properties. In addition, there is a significant amount of metal that is not incorporated in the resultant catalyst particles. This metal is superparamagnetic (SPM) and features of the magnetization curve shed light on the magnetic moment distribution of these SPM clusters. (c) 2008 American Institute of Physics.