Microstructure and Raman spectroscopy analysis of LiNiZn ferrite ceramics sintered by spark plasma method

Abstract

In this study, the effects of different parameters (sintering temperature and holding time) of spark plasma sintering (SPS) on the microstructure and magnetic properties of LiNiZn ferrite ceramics were systematically investigated, and the samples sintered by SPS (SPS samples) were compared with the samples sintered by traditional sintering (TS samples). X-ray diffraction analysis confirmed that all the samples were ferrites with spinel structure. The microstructure of the samples was analyzed by scanning electron microscopy. Compared with TS samples, SPS samples exhibited finer and more uniform grains and denser structure. At the sintering temperature of 1000 °C, SPS samples exhibited higher saturation magnetization (Ms, 79.7 emu⋅g−1) and lower ferromagnetic resonance linewidth (ΔH, 231 Oe) than TS samples (Ms: 69.3 emu⋅g−1, ΔH: 298 Oe). The phase structure and cation distribution of the samples were analyzed by Raman spectroscopy. Herein, it was speculated that the instantaneous high temperature generated by spark plasma redistributed the cations in the crystal, and the distribution mode was stabilized by rapid cooling. Based on the change of magnetic moment of ferrite molecules caused by cation distribution, a method of judging the specific Ms by fitting analysis of Lorentz curve of A1g Raman signal of ferrite ceramics was proposed. The SPS samples showed more compact and uniform microstructure and more reasonable cation distribution than TS samples, and these characteristics were mainly responsible for the remarkable improvement of magnetic properties. The results indicate that SPS method can effectively alleviate the contradiction between Ms and ΔH, and provide an alternative pathway to prepare high-performance soft magnetic ferrite.