Ferritization of Y³⁺ and Nd³⁺ ions in the solid state

The ferritization of Y³⁺ and Nd³⁺ ions in the solid state was investigated by X-ray powder diffraction, ⁵⁷Fe Moessbauer and FT-IR spectroscopies. Magnetization measurements were performed with selected samples between 4.2 and 300 K in magnetic fields up to 20 kOe. Incorporation of Nd³⁺ ions into a garnet-type structure and the formation of solid solutions of Y_3-xNd_xFe₅O₁₂ were shown. The unit-cell parameter measured for Y₃Fe₅O₁₂ was 12.359(3) angstroms, whereas for the initial molar ratio Fe₂O₃:Y₂O₃:Nd₂O₃ = 5:1:2 a value of a unit-cell parameter of 12.512(3) angstroms was measured for the garnet-type solid solution. Hyperfine magnetic fields (HMF) of 487 and 394 kOe at the a- and d-sites, respectively, were measured at 300 K for Y₃Fe₅O₁₂, while HMF of 509 kOe was measured at 300 K for NdFeO₃. The formation of solid solutions of Y_3-xNd_xFe₅O₁₂, caused a gradual shift to lower wave numbers of IR bands defined for Y₃Fe₅O₁₂. The magnetization measurements of the compounds with nominal composition (Y₂Nd)Fe₅O₁₂ and (YNd₂)Fe₅O₁₂ showed that the magnetic moments were higher than in Y₃Fe₅O₁₂. The magnetic moments at 20 kOe, corrected for presence of some orthoferrite impurity, were 5.75 μ_B and 6.45 μ_B, respectively, whereas the moment of Y₃Fe₅O₁₂ was 4.81 μ_B, and even in saturation it is only 5 μ_B. This proves that the Nd sublattice magnetization is coupled ferromagnetically to the total iron magnetization, in agreement with theoretical expectations for light rare earth garnets. The increase in magnetic moment of (YNd₂)Fe₅O₁₂ relative to Y₃Fe₅O₁₂ is less than twice of the increase for (Y₂Nd)Fe₅O₁₂. This result is probably due to the magnetic anisotropy in the Nd-rich compound. (Y₂Nd)Fe₅O₁₂ seems to exhibit a spin reorientation transition around 60 K, previously not noticed.