2495618 MCNTs magnetic carbon nanotubes 24 3022319 MCNT magnetized carbon nanotube 6 3022323 mCNT magnetic carbon nanotubes 3 2048404 MAGCNTs magnetic carbon nanotubes 2 3062628 MNTs magnetic carbon nanotubes 1 3823385 mCNT-BSA magnetic carbon nanotubes 1