Abstract The sintering temperature of an Al3+ substituted Sr-hexaferrite composite was systematically varied from 1180 °C to 1280 °C resulting in different microstructures. The grain size was found to range from a few hundred nanometers to several hundred micrometers depending on Al content and sintering temperature. Adding an Al substituted powder to a commercial powder increased the coercivity from 360 mT to 470 mT, at the same time, decreasing remanence from 350 mT to 305 mT. Magnetization and demagnetization processes from the thermally demagnetized state (TDS) and DC-demagnetized state (DCD) have been investigated systematically by in-situ magnetic force microscopy (MFM) under magnetic field. From the surface domain contrast a polarization was derived which quantitatively matches the global i.e. bulk polarization obtained by superconducting quantum interface device (SQUID) magnetometry. The shape of the initial polarization curve and the polarization from the DCD state were correlated with the in-situ MFM data revealing a distinctly different magnetization behavior depending on grain size. The presented results enable a better understanding of local nucleation mechanisms, global influences of pinning centers and further opportunities to improve rare earth (RE) free permanent magnets based on ferrites.

中文翻译：

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Al 3+ 取代Sr-六铁氧体磁化和退磁行为的原位磁力显微镜分析

摘要 Al3+ 取代的 Sr-六铁氧体复合材料的烧结温度从 1180 °C 到 1280 °C 有系统地变化，导致不同的微观结构。发现晶粒尺寸范围从几百纳米到几百微米，这取决于铝含量和烧结温度。将 Al 取代粉末添加到商业粉末中可将矫顽力从 360 mT 提高到 470 mT，同时将剩磁从 350 mT 降低到 305 mT。已通过磁场下的原位磁力显微镜 (MFM) 系统地研究了热退磁状态 (TDS) 和直流退磁状态 (DCD) 的磁化和退磁过程。从表面域对比度导出极化，其定量匹配全局即 通过超导量子界面装置 (SQUID) 磁力计获得的体极化。初始极化曲线的形状和 DCD 状态的极化与原位 MFM 数据相关，揭示了取决于晶粒尺寸的明显不同的磁化行为。所呈现的结果有助于更好地了解局部成核机制、钉扎中心的全球影响以及进一步改进基于铁氧体的无稀土 (RE) 永磁体的机会。