Content of iron cations in three biotite specimens of true trioctahedral mica were determined by Mössbauer spectroscopy, electron microprobe and wet-chemistry methods. International certified reference materials were analyzed simultaneously with micas to evaluate the accuracy of the wet-chemistry method. High precision Mössbauer spectroscopic Fe³⁺/Fe²⁺ ratios coupled with the electron microprobe iron determinations were compared with the wet-chemical data. Comparisons of data show that in wet-chemistry method powdered micas dissolve more readily during acid attack than the granular micas and thus yield higher precision and accuracy.

In this work, Ce-YIG nanoparticles with nominal composition of Y_3-xCe_xFe₅O₁₂
(x = 0, 0.1, 0.3, 0.4, 0.5, 0.6, 0.7 and 0.8) were first fabricated by sol-gel method and then the influence of the cerium substitution on the structural and magnetic properties of garnet nanoparticles were investigated by X-ray diffraction (XRD), scanning electron microscopy (SEM), fourier transform infrared (FT-IR) spectroscopy, vibrating sample magnetometer (VSM) and mössbauer spectroscopy. The XRD results showed that the maximum amount of the Ce³⁺ substitution in YIG structure is x = 0.6. Magnetic measurement shows that room temperature saturation magnetization   of nanoparticles increases up to x = 0.3 firstly and then decreases by increasing Ce content. The variation of saturation magnetization can be explained according to mössbauer studies. The mössbauer analysis showed that due to Ce substitution a and d sublattice split into two pairs of distorted and undistorted sublattice. So reduction in saturation magnetization is disscused.

In this research, Y_3-xBi_xFe₅O₁₂ x = (0, 0.1, 0.2, 0.3) were synthesized by a sol–gel method. X-ray diffraction (XRD) patterns confirmed the pure spinel structure for all samples. The magnetic properties of the samples were investigated by the vibration sample magnetometer (VSM). The results obtained from VSM showed that saturation magnetization increases up to
x = 0.1 and then decreases for x>0.1. These variations were attributed to increase of superexchange interaction and spin canting. Furthermore, a model which is based on random distribution of Bi ions in yttrium iron garnet structure was used to achieve the best fit for the Mössbauer patterns. This model explained the effect of Bi substitution on the variation of magnetic hyperfine parameters and also verified the VSM results.