Study of physical, magnetic and electrical properties of rare-earth substituted Li-Mg ferrites

Tb substituted LiMg-ferrites with nominal composition Li1.2Mg0.4 Tbx Fe(2−x)O4 (x = 0.00, 0.02, 0.04, 0.06, 0.08, 0.10) were synthesized by sol-gel auto-combustion technique. The effect on physical, magnetic and electrical properties of Li-Mg ferrites as a result of Terbium substitution is reported. X-ray diffraction analysis revealed fcc phase in all the samples along with few traces of second phase. The lattice constant initially showed increasing trend and then decreased due to the substitution of Tb which depicted partial solubility of Tb-ions in the lattice. It was observed that saturation magnetization followed decreasing trend which is attributed to the weakening of exchange interactions. However coercivity was found increasing with Tb substitution. This increase in coercivity with substitution of terbium concentration was attributed to the presence of an ultra-thin layer at the grain boundaries that subsequently impeded the domain wall motion. The high coercive Li-Mg ferrites may be suitable for high frequency microwave absorption. The dc resistivity decreased linearly with temperature for all the samples. This indicated the semiconducting behavior of these samples. Room temperature d.c. resistivity and activation energies showed similar trend thereby indicating that the samples with high resistivity have high activation energies and vice versa.