Dielectric and magnetic properties of citrate-route-processed Li-Co spinel ferrites

Cobalt‐substituted lithium ferrites (with general composition Li0.5–x /2Cox Fe2.5–x /2O4, where x = 0.0, 0.2, 0.4, 0.5 and 0.6) were prepared at lower processing temperatures (∼600 °C) by the citrate route. The single‐phase spinel structure was confirmed by X‐ray diffraction. The average particle size of calcined powders calculated by the Scherrer formula is estimated to be 8–90 nm, whereas an average particle size of ∼20 nm is observed from TEM for Co concentration x = 0.5. Average grain sizes from SEM micrographs of pellets sintered at 1000 °C (1 h) are observed to be 0.5–1 μm, much smaller than the size reported for the standard ceramic method (2.1–6.8 μm). The experimental density is observed to be 3.59–4.47 gm/cm3, which is greater than 85% of the densities evaluated from XRD. Compared with the standard ceramic method, lower dielectric constant (10–103) and higher dc resistivity (105–1010 Ω cm) is observed for Li–Co ferrites prepared by the citrate route. Improved magnetic properties, such as higher saturation magnetization (38–79 emu g–1) and Curie temperature (535 to 620 °C) are also investigated for the citrate‐route‐processed samples. These results demonstrate promising features of Li–Co ferrites in microwave applications. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)