Exchange-spring behavior in nanopowders of CoFe2O4-CoFe2

The nature of the magnetic interactions among core-shell nanoparticles of CoFe2O4-CoFe2 having an average particle size of 32 nm were investigated by delta m plots. It was found that the interactions are mainly demagnetizing in nature for nanoparticles with core diameters larger than 26 nm. For smaller values of core diameters, the exchange-spring phenomenon takes place due to the exchange-coupling at the core-shell interface. The critical thickness of the shell was estimated to be 7.8 nm. The overall results are in excellent agreement with current theoretical models. (C) 2011 American Institute of Physics. [doi:10.1063/1.3552677]