Crystal structure and magnetic properties of the Y_2.97Gd_0.03Fe_5−xLa_xO₁₂ compound: an experimental and theoretical investigation

In the present work, we have investigated the crystal structure and magnetic properties of the Y_2.97Gd_0.03Fe_5−xLa_xO₁₂ (Gd-La co-doped YIG) compound (0.00 ≤ x ≤ 0.05) obtained by the citrate sol–gel method. Rietveld refinement of the X-ray diffraction patterns provided the lattice parameter (a) values, which increased from 12.387(2) to 12.468(2) Å as the La³⁺ content increased. Raman measurements confirmed the single-phase formation, whereas transmission electron microscopy (TEM) revealed elongated and irregular particles. The Mössbauer spectroscopy confirmed the presence of Fe³⁺ and Fe²⁺ cations and the coexistence of Fe²⁺ and La³⁺ cations in the octahedral and tetrahedral sites. Nonetheless, using a phenomenological model, it was suggested that the Fe²⁺ and La³⁺ ions tend to occupy preferentially the octahedral sites in the YIG structure. Further, the correspondence between the experimental and theoretically predicted saturation magnetization values indicated that the compound stoichiometry can be described by the chemical formula Y³⁺_2.97Gd³⁺_0.03Fe³⁺_5−x−yLa³⁺_xFe²⁺_yO²⁻_12−y/2. Magnetic parameters such as saturation magnetization, anisotropy constant, remanent magnetization, and coercive field values were computed and discussed as a function of cations distribution in the YIG crystal structure.