Speaker
Dr
Mehdi Khodaei
(K. N. Toosi University of Technology)
Description
The perfect (111)-oriented $CoFe_2O_4$ and $Co_{0.8}Fe_{2.2}O_4$ thin films were grown on Pt(111)/Si substrate using pulsed laser deposition technique. The $Co_{0.8}Fe_{2.2}O_4$ film showed significantly higher magnetization and coercivity than the $CoFe_2O_4$ film. The Fe K-edge X-ray absorption near edge structure (XANES) analyses revealed that Fe in $Co_{0.8}Fe_{2.2}O_4$ film exists in $Fe^{3+}$ state leading to the actual composition of $Co_{0.8}Fe_{2.2}O^{4+δ}$. In comparison with $CoFe_2O_4$ film, the replacing of $Co^{2+}$ (with magnetic moment of 3 magneton Bohr) by $Fe^{3+}$ (with magnetic moment of 5 magneton Bohr) in $Co_{0.8}Fe_{2.2}O_4$ film can be resulted in the increase in magnetization. On the other hand, the origin of high magnetic anisotropy of cobalt ferrite lies in the unquenched orbital moment of the $Co^2+$ cations in octahedral sites of its spinel structure. Hence, the higher coercivity of $Co_{0.8}Fe_{2.2}O_4$ film (Co poor sample) should be investigated through the cation distribution analysis, which is done by X-ray magnetic circular dichroism (XMCD). The XMCD results revealed that the $Co^2+$ cations in octahedral sites of $Co_{0.8}Fe_{2.2}O_4$ film is higher than that of the $CoFe_2O_4$ film causing to the higher coercivity for $Co_{0.8}Fe_{2.2}O_4$ film.
Author
Dr
Mehdi Khodaei
(K. N. Toosi University of Technology)
