Effect of substitution of aluminium and neodymium on structural and magnetic properties of yttrium iron garnet studied using 57Fe internal field NMR

The structural and magnetic properties of non-magnetic aluminium and magnetic neodymium substituted yttrium iron garnet samples (Y_3-xAl_xFe₅O₁₂ and Y_3-nNd_nFe₅O₁₂) were investigated. Powder samples were synthesized using auto combustion route. The Rietveld refinement analysis of the samples confirmed the presence of the garnet phase and showed presence of minimal impurity phases, specifically perovskite and hematite. Substitution on Y₃Fe₅O₁₂ with Al resulted in a linear decrease in saturation magnetization, while Nd substitution showed a non-linear change. In accordance with this the Internal Field Nuclear Magnetic Resonance (IFNMR) spectrum exhibited a downward shift in peak frequency when Al was substituted, and a significant reduction in intensity with Nd substitution in yttrium iron garnet samples. Aluminium ions take up either tetrahedral or octahedral positions in the lattice, apart from the dodecahedral site, because of their smaller ionic radii. This causes a decrease in the hyperfine field that originates from Fe³⁺ ions in tetrahedral and octahedral sites. On the other hand, neodymium ions occupy dodecahedral sites and are expected not to affect Fe ions. Concurrently, an observable peak shift was not observed in the IFNMR spectrum for Nd substitution. However, Nd substitution introduced strain in the lattice due to their larger ionic radii compared to yttrium, which they replace. This strain causes disorder in tetrahedral and octahedral sites and affects ⁵⁷Fe signal intensity. The magnetic properties observed from VSM analysis is also interpreted in view of observed changes in the ⁵⁷Fe IFNMR spectrum. X-ray Photoelectron spectroscopy (XPS) was employed mainly to explore spin orbit splitting of Fe 2p state in the samples.