Composite hollow core silica/iron oxide microparticles with the ability to store an encapsulated payload and release a defined quantity "on demand" by the application of a radiofrequency magnetic field were prepared. The microparticles possessed a mesoporous silica shell with iron oxide nanoparticles bound to the external silica surface by electrostatic interaction. The size, morphology and stability of the composite particles were systematically investigated and the effect of iron oxide:silica ratio on their heating rate and the release kinetics of a model compound (vitamin B12) was determined. The composite particles were stable in time and had a high heating ability in the radiofrequency magnetic field, achieving a temperature rise of several 10's degrees C per minute. Thanks to the high heating rate, external radiofrequency field was shown to be an effective trigger mechanism for externally controlled diffusion of encapsulated material from within the hollow core at an arbitrary on-off sequence. (C) 2013 Elsevier B.V. All rights reserved.