Study on the structural-magnetic property correlation of Co-doped yttrium iron garnet based on Mössbauer spectroscopy

This study investigates the effect of Co doping on the structure and magnetic properties of yttrium iron garnet (YIG) prepared by the sol-gel method. When the doping concentration x ≤ 0.15, the introduction of Co²⁺ ions causes structural changes, with the lattice parameter increasing from 12.373 Å to 12.394 Å, and the unit-cell volume reaching a maximum of 1904.0 Å³ at x = 0.15. As a result, the magnetic properties are also modified, with the saturation magnetization (M_s) increasing from 23.1 emu/g to 28.6 emu/g. At the critical doping concentration (x = 0.15), abnormal lattice contraction and a Jahn-Teller distortion observed, accompanied by local spin disorder and fast relaxation indicated by an additional doublet in Mössbauer spectra, giving rise to optimal soft-magnetic behavior. For x > 0.15, a phase transition from Ia $\bar{3}$ d to R$\bar{3}$ occurs, which induces structural reorganization and the formation of antiphase boundaries. The lattice contraction, while M_s decreases to 23.27 emu/g and coercivity increases. These results demonstrate a direct structure-magnetism correlation and provide guidance for tailoring garnet ferrites for microwave and magneto-optical applications.