Towards hard-magnetic behavior of CoFe2O4 nanoparticles: a detailed study of crystalline and electronic structures, and magnetic properties

We have used the coprecipitation and mechanical-milling methods to fabricate CoFe2O4 nanoparticles with an average crystallite size (d) varying from 81 to similar to 12 nm when changing the milling time (t(m)) up to 180 min. X-ray diffraction and Raman-scattering studies have proved the samples crystalizing in the spinel structure. Both the lattice constant and residual strain tend to increase when t(m)(d) increases (decreases). The analysis of magnetization data has revealed a change in the coercivity (H-c) towards the hard-magnetic properties. Specifically, the maximum H-c is about 2.2 kOe when t(m) = 10 min corresponding to d approximate to 29 nm; beyond this t(m)(d) value, H-c gradually decreases. Meanwhile, the increase of t(m) always reduces the saturation magnetization (M-s) from similar to 69 emu g(-1) for t(m) = 0 to 35 emu g(-1) for t(m) = 180 min. The results collected as analyzing X-ray absorption data have indicated a mixed valence state of Fe-2+,Fe-3+ and Co2+ ions. We think that the migration and redistribution of these cations between the tetrahedral and octahedral sites together with lattice distortions and defects induced by the milling process have impacted the magnetic properties of the CoFe2O4 nanoparticles.

Automated summary

We fabricated CoFe2O4 nanoparticles with varying crystallite size using coprecipitation and mechanical milling methods. X-ray diffraction and Raman scattering studies confirmed the spinel structure of the samples. The lattice constant and residual strain increased with increasing milling time, leading to changes in the magnetic properties. Analysis of magnetization data revealed changes in coercivity and saturation magnetization. X-ray absorption data indicated a mixed valence state of Fe-2+,Fe-3+, and Co2+ ions, suggesting the migration and redistribution of these cations and lattice distortions impacted the magnetic properties of the nanoparticles.