Feasibility studies of magnetic particle-embedded carbon nanotubes for perpendicular recording media

Nano-sized magnetic particles were successfully used as the catalysts to synthesize magnetic metal-encapsulated carbon nanotubes (CNTs) or nanoparticles on Si wafers in a microwave plasma electron cyclotron resonance chemical vapor deposition (ECR-CVD) system with CH4 and/or H-2 as source gases. The magnetic catalyst materials, including Fe-Pt, Co-Pt, Nd2Fe14B, Fe and Fe-Ni, were first deposited on Si wafers by a physical vapor deposition (PVD) method, with subsequent plasma treatment for nanoparticle transformation. The main process parameters include catalyst materials, hydrogen plasma catalyst pretreatment and deposition temperature. For applications in magnetic media, the process has the following advantages: perpendicularly aligned CNTs or nanoparticles; tip-growth CNTs; well-distributed magnetic particles; detectable magnetic field in each particle; high tube number density (up to 134 Gtubes/inch(2) for Fe-assisted CNTs); favorable catalyst size; higher shape and induced anisotropy; and nanostructures that can be manipulated. The catalyst particle sizes of Fe, Nb2Fe14B and Fe-Pt (35-40 mn in diameter) are uniform and greater than but close to the critical optimum size or single domain size, which favor a higher coercive force. The greatest coercive force can reach 750 Oe for Fe-assisted CNTs at a deposition temperature of 715 degreesC, which is comparable with values reported in the literature. The coercive force difference between the vertical and horizontal directions can reach 300 Oe for Fe-assisted CNTs, and 355 Oe for Nb2Fe14B-assisted CNTs. (C) 2002 Elsevier Science B.V. All rights reserved.