Iron powder particles with a mean diameter of about 2 µm have been charged and trapped in an r.f. plasma with an electron density in the order of 108–109 cm-3. The iron particles were coated with a surrounding aluminum layer by d.c. magnetron sputtering during their confinement. The plasma parameters at r.f. and magnetron operation were confirmed by Langmuir probes, self-excited electron resonance spectroscopy and energy-resolved mass spectrometry, respectively. The coated powder particles were characterized by scanning electron microscopy (SEM) and X-ray photoelectron spectroscopy (XPS). The results of the surface analysis indicate that coating iron powder particles with a close and compact aluminum film by d.c. magnetron sputtering while they are trapped in a weak r.f. plasma is an attractive procedure for powder modification.