Effects of isovalent substitution on structural and magnetic properties of nanocrystalline Y3−xGdxFe5O12 (0 ≤ x ≤ 3) garnets

We fabricated Gd-doped Y₃Fe₅O₁₂ (YIG) nanoparticles by a modified sol–gel method. We investigated the effects of isovalent Gd³⁺-ion substitution on the structural and magnetic properties of Y_3−xGd_xFe₅O₁₂ (0 ≤ x ≤ 3) nanoparticles. Isovalent Gd³⁺-ion substitution for Y³⁺ leads to lattice expansion and change in the Fe(a)–O–Fe(d) bond angle. The X-ray photoemission spectroscopy and Mössbauer measurements revealed a high-spin state of Fe³⁺. The Mössbauer analysis showed an increase in the Fe_(d)³⁺/Fe_(a)³⁺ ratio, indicating a relocation of Y³⁺ ions at the dodecahedral sites and Fe³⁺ ions at the octahedral sites. The magnetic properties could be explained in terms of magnetic-structural evolution with increasing Gd³⁺ content. The field dependence of magnetization indicated a clear decrease of the magnetization while the magnetic anisotropy first decreases and then increases with the increase of Gd³⁺ content. These Gd³⁺-ion-substituted nanocrystalline garnet ferrites are suitable for use in a variety of magneto-optical applications.