Magnetic and Mössbauer spectroscopy studies of hollow microcapsules made of silica-coated CoFe 2 O 4 nanoparticlesстатья
Статья опубликована в высокорейтинговом журнале
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Дата последнего поиска статьи во внешних источниках: 28 апреля 2016 г.
Аннотация:The hollow microcapsules made of silica-coated CoFe2O4 nanoparticles were synthesized using
chemical co-precipitation, followed by the sol–gel method. Poly(MMA-co-MAA) microspheres
were used as a core template which can be completely removed after annealing at 450 °C. The
microcapsules are monodisperse with the outer diameter of about 450 nm and the thickness of
the shell is about 50 nm. The nanoparticles of Co-ferrite are single crystalline. The size of the
nanoparticles and magnetic properties of CoFe2O4/SiO2 hollow spheres can be tuned with high
accuracy at the annealing stage. The Mössbauer data indicate that CoFe2O4 ferrite is an inverse
spinel, in which Fe3+ and Co2+ ions are distributed in both octahedral and tetrahedral sites with
the inversion degree close to the bulk ferrite value. At low temperature the CoFe2O4/SiO2
nanoparticles are in antiferromagnetic (AFM) state due to the canted or triangular magnetic
structure. Under heating in the applied field, AFM structure transforms to the ferrimagnetic (FM)
structure, that increases the magnetization. The Mössbauer data revealed that the small size
CoFe2O4/SiO2 particles do not show superparamagnetic behavior, but they transit to the
paramagnetic state by the jump-like first order magnetic transition (JMT). This effect is a specific
property of the magnetic nanoparticles isolated by inert material. 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 bio-separation.