Synthesis, magnetic and Mössbauer spectroscopic studies of Cr doped lithium ferrite nanoparticles

Lithium-based ferrites are promising and potential magnetic materials for microwave applications. They possess a spinel (AB 2 O 4 ) type crystal structure, where the distributions of metal cations over the tetrahedral (A) and octahedral (B) voids play a crucial role for exhibiting different physical properties. Among various parameter of synthesis, pH is an important factor that influences the cation distribution over A and B voids, overall growth of the nanoparticles and different physical properties. In the present work single phase Cr substituted lithium ferrite nanoparticles have been synthesized by the sol–gel method at different pH. The phase identification and crystallite size have been probed by X-ray diffraction studies. The crystallite size changes by 44.2–48.8 nm upon varying the pH from 3.5 to 11.5. In order to investigate the cations distribution at A/B sites, Mossbauer spectroscopic measurements were done. The values of magnetic hyperfine field obtained from the Mossbauer data for the A and B sites are ≈49.5 T and 51 T, respectively. Moreover, it is observed that the area ratio of B site to A site increases with increasing the pH. This observation further suggests that the B site is more preferable for Fe 3+ cations at higher pH than the A site. The magnetic parameter such as saturation magnetization ( M s ), remanent magnetization ( M r ), coercive field ( H C ) and squareness ( S ) are determined by vibrating sample magnetometer (VSM) measurements, which show a consistent increase with increasing pH. The reason for the variation in magnetic properties has been explained on the basis of increased Fe 3+ cation occupancies at the B site and size effect, which is well supported by Mossbauer spectroscopic and XRD studies.