The SmCo₅ rare-earth hard magnet has the largest anisotropy field among all known magnetic materials, 32 MA m⁻¹ (400 kOe), while the obtainable coercivity (H_c) is usually less than 30% of the anisotropy field. The coercivity is enhanced when the grain size (spherical shape) is in the stable single-domain size (SSDS) range. Theoretical calculation predicts the SSDS range of SmCo₅ to be 740–870 nm, however, at present, there has been no experimental data supporting this claim. Herein, we used a chemical method for tuning the average particle size (APS) of SmCo₅ resulting in sizes ranging from 228 nm to 1191 nm. We find, that the morphology and composition of the precursor plays a decisive role in determining the composition and APS of the final product. A maximum coercivity of 2.6 MA m⁻¹ (33.1 kOe) was obtained for an APS of 823 nm. SEM images and recoil loops demonstrate that samples with high coercivity are homogeneous and the demagnetization process happens simultaneously between multiple phases showing single-phase magnetic behavior. Henkel plots and δM plots verify the existing of strong exchange coupling interaction between particles, resulting in high M_r/M_s ratios. This is the first reported systematic optimization study of the coercivity of SmCo₅ based on single-domain theory and the optimized APS matches remarkably well the predicted SSDS range.

中文翻译：

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通过粒度控制提高SmCo5磁体的矫顽力

在所有已知的磁性材料中，SmCo ₅稀土硬磁体的各向异性场最大，为32 MA m ^-1（400 kOe），而可获得的矫顽力（H _c）通常小于各向异性场的30％。当晶粒尺寸（球形）在稳定的单畴尺寸（SSDS）范围内时，矫顽力会提高。理论计算预测，SmCo ₅的SSDS范围为740-870 nm，但是，目前尚无实验数据支持该主张。在这里，我们使用化学方法调整SmCo ₅的平均粒径（APS）尺寸范围从228 nm到1191 nm。我们发现，前体的形态和组成在决定最终产品的组成和APS中起着决定性的作用。对于823 nm的APS，获得了2.6 MA m ^-1（33.1 kOe）的最大矫顽力。SEM图像和反冲回路表明，高矫顽力的样品是均匀的，并且退磁过程同时发生在显示单相磁行为的多相之间。汉高图和δ中号重复验证颗粒之间强的交换耦合作用的现有，导致高的中号_{- [R} /中号_小号比率。这是首次报道的SmCo矫顽力的系统优化研究₅基于单域理论和优化的APS匹配非常好预测SSDS范围。