Effect of Tb substitution on structural, magnetic and electrical properties of magnesium ferrites

A series of Mg1−xTbxFe2O4, ferrite samples (0.0 ≤ x ≤ 0.2) were synthesized by the ceramic method and were characterized by using X-ray diffraction, Fourier transform infrared spectroscopy (FTIR) and vibrating sample magnetometery. The XRD patterns showed the single phase ferrites up to x ≤ 0.04 without other secondary phase. The lattice constant increases slightly as a function of terbium content up to x = 0.04 and decreases for x > 0.04. The increase is attributed to the difference in the ionic radii of the cations involved and decrease led to the formation of secondary phase (TbFeO3). The bulk density was found to increase from 3.5 to 4.6 (g/cm3) with the increase of terbium concentration. FTIR spectra exhibited two significant absorption bands in the wave number range of 370–1500 cm−1 which confirm the spinel structure and completion of chemical reaction. The magnetic properties revealed a decrease in the saturation magnetization as a function of Tb content. An unexpected increase in magnetization at the Tb content of 0.02 could be due to the migration of Mg ions towards tetrahedral sites, consistent with the results of FTIR. Coercivity variations are attributed to the magneto-crystalline anisotropy. The resistivity increased with the substitution of terbium relative to the sample undoped with terbium while the drift mobility was found to decrease.