Magnetic order and finite size effects in nanosized doped ferrite particles

B. PIANCIOLA; E. LIMA JR.; R.D. ZYSLER

Rodas

Simposio; Joint European Symposia ? JEMS 2013; 2013

JEMS commmitte

Finite-size effects dominate the magnetic properties of nanosized particles and become important as the particle size decreases, due to the increasing surface to volume ratio. We have focused on the size dependence of the magnetic properties and the surface effects of CoFe2O4 nanoparticles in the size range 2-7nm of diameter with very narrow grain size distributions. Additionally, we compared these results with nickel ferrite nanoparticles.Ferrite nanoparticles were synthesized by high temperature decomposition of Fe(acac)3 and Co(acac)2 or Ni(acac)2. The nanoparticle size was controlled varying the reaction temperature and the metallic precursor/surfactant ratio[1].The characterization was performed with TEM, XRD. Magnetic properties were determined from the temperature dependence of magnetization and magnetization isotherms measurements and Mössbauer spectroscopy. The samples exhibit characteristic of a superparamagnetic system showing an increase in the blocking temperatures with the particle size. It is observed a size dependence of the ferrimagnetic order in the magnetization curves and Mössbauer spectra. Larger particles have a bulk-type magnetic ordering while the smaller ones have broken the ferrimagnetic order behaving as paramagnetic and/or superparamagnetic of small clusters, depending on temperature. The nanoparticles of 4.5nm of diameter show a mixed behavior indicating that this particle size is the crossover between the system perfectly ordered and the magnetically disorder one[2].REFERENCES[1] J.M. Vargas et al, Nanotech. 16(2005), 1474.[2] R.D. Zysler et al, J. Magn. Magn. Mater. 266(2003), 233.