Graphite plates were Ar+ ion-sputtered with a simultaneous Fe supply at room temperature. The sputtered surfaces were characterized by various kinds of carbon compostites, such as conical protrusions with and without single carbon nanocomposite fibers (CNCFs) on the top, depending on the Fe supply rates. The CNCFs thus grown were confirmed to be amorphous-like fibers without a hollow structure and possess no distinct boundary between the cone and the CNCF by transmission electron microscope. As revealed by their compositional analysis, CNCFs surely composed of carbon and iron. Since the various kind of metals can be doped into the room-temperature grown carbon nanofibers, this ion-irradiation method is believed to be promising as a new approach to synthesize one-dimensional nanomaterials at low temperatures.