Apparatus and methods are described for use with a heating device (26) configured to heat at least a portion of a subject's body. A nanoparticle (22) is configured to be administered to the subject, the nanoparticle including at least one inner core (30) that includes a magnetic material having a Curie temperature； a phase-change-material layer (31) that surrounds the inner core and that comprises a phase-change material that is configured to absorb latent heat of fusion by undergoing a phase change selected from the group consisting of: solid to liquid, and gel to liquid, the phase-change occurring at a phase-change temperature that is lower than the Curie temperature； and an outer layer (32) disposed around the phase-change-material layer, the outer layer comprising a plurality of nano-subparticles (34) that are separated from one another, such as to form a segmented layer. Other applications are also described.
