Structural, Electrical, and Microstructure Properties of Nanostructured Calcium Doped Ba-Hexaferrites Synthesized by Sol-Gel Method

摘要

Nanostructured M-type hexaferrite Ba_(1-x)Ca_x Fe_(11.5)Cr_(0.5)O_(19) (x = 0.0-0.5) powders have been synthesized by means of the sol-gel autocombustion method. The materials are characterized by differential scanning calorimetry, thermogravimetry, Fourier transform infrared spectroscopy, X-ray diffraction, scanning electron microscopy, energy dispersive X-ray spectroscopy, and vibrating sample magnetometry. X-ray diffraction analysis confirms the formation of M-type hexagonal phase and few traces of α-Fe_2O_3 are also observed. The c/a ratio falls in the expected range from a value of 3.97 to 3.94 of M-type hexaferrites. The average crystallite size is found to be in the range 15 to 36 nm, which is good enough to obtain the suitable signal-to-noise ratio in the high-density recording media. DC electrical resistivity at room temperature enhances up to 11.2 × 10~9 Ωcm (x = 0.4) and then drops upon increasing the Ca~(2+) contents further. The magnetic properties such as saturation magnetization (M_s), remanence (M_r), squareness ratio (M_r/M_s) and coercivity (H_c) are calculated from the M-H-loops. The maximum magnetization and remanence reduces from a value of 52 to 33 and 33 to 16 emu/g, respectively, which attributes to the decrease of magnetic moment, and hence reduction in the superexchange interaction. The coercivity enhances from 4378 to 4706 Oe, which attributes to the increase in magnetocrystalline anisotropy due to the reduction of particle size. Owing to these properties, the synthesized nanomaterials can be considered useful for high-density recording media and permanent magnets.