Аннотация:The functional polymer (PMA-co-MAA) latex microspheres were used as a core template to prepare magnetic hollow
spheres consisting of CoFe2O4 / SiO2 composites. The spinel type crystal structure of CoFe2O4 ferrite is formed under
annealing, whereas the polymer cores are completely removed after annealing at 450°C. Magnetic and Mössbauer
spectroscopy measurements reveal very interesting magnetic properties of the CoFe2O4 / SiO2 hollow spheres strongly
dependent on the particle size which can be tuned by the annealing temperature. In the ground state of low
temperatures, the CoFe2O4 nanoparticles are in antiferromagnetic state due to the canted magnetic structure. Under
heating in the applied field, the magnetic structure gradually transforms from canted to collinear, which increases the
magnetization. The Mössbauer data revealed that the small size CoFe2O4 / SiO2 particles (2.2 – 4.3 nm) do not show
superparamagnetic behavior but transit from the magnetic to the paramagnetic state by a jump-like magnetic transition
of the first order This effect is a specific property of the magnetic nanoparticles isolated by inert material, and can be
initiated by internal pressure creating at the particle surface. The suggested method of synthesis can be modified with
various bio-ligands on the silane surface, and such materials can find many applications in diagnostics and bioseparation.