Co²⁺ Distribution and the Related Magnetic Evolution in Ca-substituted Spinel CoFe₂O₄

Magnetic properties of cobalt ferrites with a portion of CoSUP2+/SUP ions being replaced by CaSUP2+/SUP were investigated by vibrating-sample magnetometry (VSM). The CaSUBx/SUBCoSUB1-x/SUBFe₂O₄ (x ≤ 0.2) specimens were prepared as thin films by a sol-gel deposition method. According to the VSM results, the saturation magnetization (MSUBS/SUB) of the Ca-substituted ferrite decreased from that of CoFe₂O₄ proportional to the Ca composition x. Raman spectral analyses revealed that the Ca-substituted ferrites had a lower tetrahedral CoSUP2+/SUP population in the spinel lattice compared to CoFe₂O₄. The decreasing trend of MSUBS/SUB is consistent with the result of theoretical evaluation in which the relative population of CoSUP2+/SUP ions among the tetrahedral and octahedral sites is proportional to the relative Raman scattering intensities of 615 and 470 cmSUP-1/SUP peaks, respectively.