Pure dipolar-interacted CoFe2O4 nanoparticles and their magnetic properties

The mono-dispersed and uniform CoFe2O4 nanoparticles were synthesized by the thermal decomposition of Fe(acac)3 and Co(acac)2. Then the CoFe2O4 nanoparticles were diluted in amorphous SiO2 matrix with different CoFe2O4 nanoparticles’ concentrations. All samples show the positive or negative exchange bias behavior, indicating the presence of canted spin layer at the CoFe2O4 nanoparticles’ surface. The large effective anisotropy constant (3.38 × 106 erg/cm3) was observed, which can be attributed to the induced surface anisotropy by the canted surface spins. The reduced magnetization (Mr/Ms) was dominated by the interparticle dipolar interaction while the coercivity (Hc) was determined by the synergistic effects of the surface anisotropy, interparticle dipolar interaction and interface effect. By suitably diluting CoFe2O4 in the SiO2 matrix, the high Hc (3056 Oe) and the Mr/Ms (0.63) can be obtained, which is larger than most of those reported before. The present work is meaningful for revealing the underlying mechanism in nano-scaled magnetic system and improving the magnetic performance.