Relationship between the Microstructure, Local Magnetism and Coercivity in Ga-Containing Nd-Fe-B Sintered Magnets
Relationship between the Microstructure, Local Magnetism and Coercivity in Ga-Containing Nd-Fe-B Sintered Magnets
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DOI：
10.2139/ssrn.3697716
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发表时间：
2020-10
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通讯作者：
D. Billington;H. Okazaki;K. Toyoki;Y. Kotani;Y. Takada;Takashi Sato;Y. Kaneko;A. Kato;T. Sasaki;T. Ohkubo;K. Hono;Tetsuya Nakamura
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作者：
D. Billington;H. Okazaki;K. Toyoki;Y. Kotani;Y. Takada;Takashi Sato;Y. Kaneko;A. Kato;T. Sasaki;T. Ohkubo;K. Hono;Tetsuya Nakamura
通过在25 ° C和800°C之间的温度下的原位高温X射线衍射来识别包括各向同性的含Ga的Nd-Fe-B烧结磁体的体微结构的晶相。将晶相的温度依赖性体积分数与作为退火温度的函数的矫顽磁力进行比较，发现大的矫顽磁力增强与晶状Nd 6（Fe，Ga）14相的存在显着相关。扫描软X射线吸收显微镜测量被用来直接观察各向异性的烧结和优化退火样品中的Fe和Nd的分布，并证明表面微观结构是类似于散装。Fe L3-边缘X射线磁性圆二色性测量用于直接映射各向异性烧结和最佳退火样品的断裂表面的退磁过程。在烧结样品中，组成不同区域的退磁曲线都具有相同的形状，但具有仅取决于X射线吸收测量的探测深度内的Fe含量的最大磁信号。在最佳退火条件下，不同成分区域的退磁曲线具有不同的形状，没有任何晶界覆盖的暴露Nd 2Fe 14 B晶粒的退磁率比有晶界覆盖的晶粒的退磁率低得多。这提供了在退火时形成的晶界相能够通过交换解耦Nd 2Fe 14 B晶粒来保护Nd 2Fe 14 B晶粒免于磁化反转的证据。
The crystalline phases that comprise the bulk microstructure of an isotropic Ga-containing Nd-Fe-B sintered magnet are identified by in situ elevated-temperature x-ray diffraction for temperatures between 25 and 800°C. Comparing the temperature-dependent volume fractions of the crystalline phases with the coercivity as a function of annealing temperature reveals that the large coercivity enhancements are remarkably well-correlated with the existence of a crystalline Nd6(Fe,Ga)14 phase. Scanning soft x-ray absorption microscopy measurements are used to directly observe the distribution of Fe and Nd in anisotropic as-sintered and optimally-annealed samples and demonstrate that the surface microstructure is similar to bulk. Fe L3-edge x-ray magnetic circular dichroism measurements are used to directly map the demagnetization process in the fractured surfaces of anisotropic as-sintered and optimally-annealed samples. In the as-sintered sample, the demagnetization curves of compositionally different regions all have the the same shape but with a maximum magnetic signal that only depends on the Fe content within the probing depth of the x-ray absorption measurements. In the optimally-annealed sample, the demagnetization curves from compositionally different regions have rather different shapes and the exposed Nd2Fe14B grains without any grain boundary coverage have much lower coercivity than those with. This provides evidence that the grain boundary phase that forms upon annealing is able to protect the Nd2Fe14B grains from magnetization reversal by exchange-decoupling the Nd2Fe14B grains.