Synthesis and magnetic properties of CoFe2/CoFe2O4 nanoparticles diluted in the MgO matrix

Well-dispersed 16-nm CoFe2O4 particles (a) were synthesized and then some nanoparticles were coated by MgO (b) followed by the reduction in a H2/N2 gas mixture to prepare CoFe2/MgO (c). CoFe2/MgO was oxidized in the open air at 500 °C and 900 °C to prepare CoFe2(core)/CoFe2O4(shell)/MgO (d) with the CoFe2/CoFe2O4 mass ratio being 25.4% and 4.7%, respectively. By comparing the experimental and calculated data, the magnetic properties were discussed in detail. Our results revealed that the correlation between the remanence Mr to saturation magnetization ratio Mr/Ms and maximum dipolar field Hdip roughly follows Mr/Ms∝1/lgHdip (e and f), independent to the moment and concentration of magnetic particles.