Magnetic Properties of Fe-alloy Catalyst Nanoparticles for Carbon Nanofiber Synthesis*

The magnetic properties of Fe-alloy nanoparticles, used as catalysts in vertically-aligned carbon nanofiber (VACNF) growth, has been investigated. First, Fe and Co or Ni were co-sputtered onto Si substrates in order to make a catalyst alloy film. These substrates were then placed in a plasma-enhanced CVD chamber with a substrate temperature of 700$^{\circ}$C and a flowing mixture of acetylene (C$_2$H$_2$) and ammonia (NH$_3$) gas. During the PECVD, the catalyst film breaks into nanoparticles of 50--200~nm and VACNFs are grown. EDX shows that the catalyst nanoparticles nominally have the deposited alloy ratio. In addition, the nanoparticles are still magnetic and have a non-negligible remanence and hysteresis. Their magnetic properties are investigated by SQUID magnetometry in applied field of $|H| \le 50$~kOe and temperatures of 5--400~K. In addition, AC susceptibility studies give energy loss characteristics of the co-synthesized VACNF system.