Pure dipolar-interacted CoFe_2O_4 nanoparticles and their magnetic properties

摘要

The mono-dispersed and uniform CoFe_2O_4 nanoparticles were synthesized by the thermal decomposition of Fe(acac)_3 and Co(acac)_2. Then the CoFe_2O_4 nanoparticles were diluted in amorphous SiO_2 matrix with different CoFe_2O_4 nanoparticles' concentrations. All samples show the positive or negative exchange bias behavior, indicating the presence of canted spin layer at the CoFe_2O_4 nanoparticles' surface. The large effective anisotropy constant (3.38 × 10~6 erg/cm~3) was observed, which can be attributed to the induced surface anisotropy by the canted surface spins. The reduced magnetization (M_r/M_s) was dominated by the interparticle dipolar interaction while the coercivity (H_c) was determined by the synergistic effects of the surface anisotropy, interparticle dipolar interaction and interface effect. By suitably diluting CoFe_2O_4 in the SiO_2 matrix, the high H_c (3056 Oe) and the M__r/M_s (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.