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 (AB₂O₄) 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, Mössbauer spectroscopic measurements were done. The values of magnetic hyperfine field obtained from the Mössbauer 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 Fe³⁺ 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 Fe³⁺ cation occupancies at the B site and size effect, which is well supported by Mössbauer spectroscopic and XRD studies.