Observation of surface effects in La-doped CoFe2O 4/SiO2 nanocomposites

0440078 - ÚACH 2015 RIV GB eng C - Conference Paper (international conference)
Burianova, S. - Vejpravová, J. - Holec, Petr - Nižňanský, D. - Plocek, Jiří
Observation of surface effects in La-doped CoFe2O 4/SiO2 nanocomposites.
IOP conference series: Materials science and engineering. Vol. 18. Bristol: IOP Publishing, 2011, 022015. Symposium. ISSN 1757-8981.
[International Congress on Ceramics /3./. Osaka (JP), 14.11.2010-18.11.2010]
R&D Projects: GA ČR GAP108/10/1250
Keywords : Amorphous Silica matrix * Applied field * Blocking temperature * Cation distributions * Field cooled
Subject RIV: CA - Inorganic Chemistry

In magnetism of nanoparticles, surface spin effects play a key role. The so-called spin canting at the surface leads either to lowering of saturation magnetization, or even to lack of saturation in high magnetic fields. The value of the saturation magnetization depends on cation distribution within the spinel network and on the spin canting angles. We have investigated structure and magnetic behavior of CoFe2O4 nanoparticles doped with La (Co1-xLaxFe2O4, x 0.05 - 0.5 and CoLaxFe2-xO4, x 0.05 - 0.2) embedded in amorphous silica matrix prepared by a sol-gel method. The samples were characterized using X-ray diffraction and TEM. The zero-field cooled and field cooled measurements of magnetization showed that the blocking temperature is well above the room temperature. The high coercivity was observed (up to 2 T at 10 K) and no saturation of the magnetization even in applied field of 7 T was obtained, suggesting considerable spin canting effects. Finally, the Mossbauer spectroscopy under magnetic field and down to low temperature was performed to determine the cation distribution and the spin canting angles.
Permanent Link: http://hdl.handle.net/11104/0243306