Dielectric and magnetic properties of Y3−xTbxFe5O12 ferrimagnets

Y3−xTbxFe5O12 (x = 0−3) were prepared by the solid state reaction at 1350 °C. X-ray diffraction confirmed the obtained samples of a pure garnet phase. The dielectric responses were investigated over a wide frequency and temperature range. Two large, step-like increases of dielectric constants were observed at 20–100 °C and 170–270 °C, respectively. Thermal activation of the polarons related to Fe2+ was responsible for the observed dielectric behaviors. The Fe2+/Fe3+ hopping process was faster in Tb3Fe5O12 than in Y3Fe5O12. The saturation magnetization versus temperature measurements revealed the existence of a compensation point for all Y3−xTbxFe5O12 with x > 0, owing to the cancellation of net Fe3+ moments by Tb3+. The compensation temperature fell from 256 K at x = 3 to below 77 K at x = 1, because the reduced moment by the Tb3+ number reduction had to be supplemented by the increased Tb3+ interaction at lower temperature.