Size-Dependent Magnetic and Magneto-Optical Properties of Bi-Doped Yttrium Iron Garnet Nanopowders

Bi-doped yttrium iron garnet nanopowders were successfully synthesized by a combustion method at different synthesis conditions, and the evolution of their structural, magnetic, and magneto-optical properties has been studied by various methods. X-ray diffraction analysis revealed that crystallite size increases with increase as in annealing time (t_A) well as in annealing temperature (T_A) and varied from 15.2 nm (T_A = 650 °C, t_A = 0.5 h) to 44.5 nm (T_A = 800 °C, t_A = 12 h). The magnetic hysteresis loops exhibit behavior characteristic of soft magnetic materials; herewith, the saturation magnetization demonstrates a growing trend with increasing crystallite size (D). The behavior of the coercivity indicates that, at room temperature, the transition between single-domain and multidomain states occurs at D = 35.3 nm. It was found that the size effect in the MCD spectra is clearly observed for the samples with crystallite sizes less than 42.2 nm for an intersublattice charge-transfer transition and a crystal-field tetrahedral transition. The influence of cation redistribution on the observed changes has been discussed.