Carpet-like flakes (area less than or equal to 9 mm(2); thickness < 50 mum) of well-aligned Co-filled multi-walled carbon nanotubes were grown by decomposition of cobaltocene. The nanotubes have outer diameters of 50-90 nm and a metal core of 15-30 nm diameter. They are discontinuously filled with f.c.c.-Co nanowires of up to a few micrometers in length. Magnetometry studies show a weak uniaxial magnetic anisotropy with the easy axis along the nanowires and a high coercivity of about 59 mT. Electron holography provides information about the magnetic characteristics of individual nanowires. (C) 2004 Elsevier B.V. All rights reserved.