织构化与各向同性Nd-Fe-B基纳米复合材料的自旋结构：晶体织构与自旋织构相关联的证据
Spin structures of textured and isotropic Nd-Fe-B-based nanocomposites: Evidence for correlated crystallographic and spin texture
AI总结：
本研究通过磁小角中子散射等技术对比织构化与各向同性Nd₂Fe₁₄B/α-Fe纳米复合材料的磁微结构，发现织构样品颗粒内存在纳米尺度非均匀磁化区，且晶体织构与自旋织构可能存在关联。
摘要：
我们报道了一项针对织构化与各向同性$\boldsymbol{\rm Nd_2Fe_{14}B}/\boldsymbol{\rm α}$-$\boldsymbol{\rm Fe}$纳米复合材料磁微结构的对比研究结果，研究采用了磁测法、透射电子显微镜、同步辐射X射线衍射，尤其是磁小角中子散射（SANS）技术。对织构化样品的磁中子数据进行分析，并计算自旋失配SANS截面的关联函数后发现，在剩磁状态下，颗粒内部纳米尺度（约40–50 nm）存在非均匀磁化区域。本文讨论了这种自旋无序的可能成因：它可能源于薄晶界层（其材料参数与$\rm Nd_2Fe_{14}B$晶粒不同），也可能反映了（热压引入的）晶体缺陷的存在，或是$\rm Nd_2Fe_{14}B$晶粒的磁晶各向异性轴取向分布存在离散性。X射线粉末衍射数据显示，在垂直于压制方向的方向上存在晶体织构——这一发现可能与磁SANS数据推断出的磁化分布织构的存在相关。
英文摘要：
We report the results of a comparative study of the magnetic microstructure of textured and isotropic $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}/α$-$\mathrm{Fe}$ nanocomposites using magnetometry, transmission electron microscopy, synchrotron x-ray diffraction, and, in particular, magnetic small-angle neutron scattering (SANS). Analysis of the magnetic neutron data of the textured specimen and computation of the correlation function of the spin misalignment SANS cross section suggests the existence of inhomogeneously magnetized regions on an intraparticle nanometer length scale, about $40-50 \, \mathrm{nm}$ in the remanent state. Possible origins for this spin disorder are discussed: it may originate in thin grain-boundary layers (where the materials parameters are different than in the $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$ grains), or it may reflect the presence of crystal defects (introduced via hot pressing), or the dispersion in the orientation distribution of the magnetocrystalline anisotropy axes of the $\mathrm{Nd}_2\mathrm{Fe}_{14}\mathrm{B}$ grains. X-ray powder diffraction data reveal a crystallographic texture in the direction perpendicular to the pressing direction -- a finding which might be related to the presence of a texture in the magnetization distribution, as inferred from the magnetic SANS data.
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