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

摘要

Cobalt-substituted lithium ferrites (with general composition Li_(0.5-x/2)Co_xFe_(2.5-x/2)O_4, where x = 0.0, 0.2, 0.4, 0.5 and 0.6) were prepared at lower processing temperatures (～600℃) 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℃ (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/cm~3, which is greater than 85% of the densities evaluated from XRD. Compared with the standard ceramic method, lower dielectric constant (10-10~3) and higher dc resistivity (10~5-10~(10) 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℃) are also investigated for the citrate-route-processed samples. These results demonstrate promising features of Li-Co ferrites in microwave applications.