Pure dipolar-interacted CoFe2O4 nanoparticles and their magnetic properties

• The mono-dispersed CoFe2O4 nanoparticles with the uniform size of 10.5 ± 2 nm were synthesized by the thermal decomposition of metals acetylacetonates in solvents with high boiling point.
• The large coercivity (3056 Oe) and the remanence ratio (0.63) were obtained by diluting CoFe2O4 nanoparticles into the SiO2 matrix with a suitable concentration.
• The surface anisotropy and interparticle dipolar interaction affect the magnetic performance and magnetic ordering state.
• It was observed that the Mr/Ms ratio was dominated by the interparticle dipolar interaction.

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.

The mono-dispersed CoFe2O4 nanoparticles with the uniform size of 10.5 ± 2 nm were first synthesized and then they were embedded in amorphous SiO2 matrix with different CoFe2O4 nanoparticles’ concentrations. The large coercivity (3056 Oe) and the remanence ratio (0.63) were obtained by suitably diluting CoFe2O4 nanoparticles into the SiO2 matrix. The reciprocal of the absolute maximum of δm and the Mr/Ms ratio behave in the same trend (as shown in (e)), indicating that the Mr/Ms ratio was dominated by the interparticle dipolar interaction. The present work is meaningful for revealing the underlying mechanism in nano-scaled magnetic system and improving the magnetic performance.Figure optionsDownload as PowerPoint slide