Heat release in magnetic nanoparticles in AC magnetic fields

Using the method of gas-phase synthesis, nanocrystalline powders on the basis of iron oxides (defect magnetite Fe3O4), with an average size of 16, 21, 30, and 44 nm, and nanocomposites on the basis of iron and cobalt encapsulated into carbon, with an average size less than 10 nm have been prepared. The nano-particles placed into a buffer solution were subjected to the action of an ac (rotating and axial) magnetic field. The rotating field ensures higher values of heat release as compared to the axial field in media with a comparatively low viscosity. The greatest values of heat liberation in the axial field at frequencies to 100 kHz are observed for the iron-oxide particles with an average size on the order of 16 nm (up to 20 W/g). For the nano-composite on the basis of Fe@C and Co@C, the specific heat losses in rotating fields are greater than for the axial field (10 and 26 W/g, respectively).