We map the three-dimensional strain heterogeneity within a single core-shell Ni nanoparticle using Bragg coherent diffractive imaging. We report the direct observation of both uniform displacements and strain within the crystalline core Ni region. We identify non-uniform displacements and dislocation morphologies across the core–shell interface, and within the outer shell at the nanoscale. By tracking individual dislocation lines in the outer shell region, and comparing the relative orientation between the Burgers vector and dislocation lines, we identify full and partial dislocations. The full dislocations are consistent with elasticity theory in the vicinity of a dislocation while the partial dislocations deviate from this theory. We utilize atomistic computations and Landau–Lifshitz–Gilbert simulation and density functional theory to confirm the equilibrium shape of the particle and the nature of the (111) displacement field obtained from Bragg coherent diffraction imaging (BCDI) experiments. This displacement field distribution within the core-region of the Ni nanoparticle provides a uniform distribution of magnetization in the core region. We observe that the absence of dislocations within the core-regions correlates with a uniform distribution of magnetization projections. Our findings suggest that the imaging of defects using BCDI could be of significant importance for giant magnetoresistance devices, like hard disk-drive read heads, where the presence of dislocations can affect magnetic domain wall pinning and coercivity.

中文翻译：

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单个磁性纳米晶体中异质应变和缺陷的纳米级映射

我们使用布拉格相干衍射成像在单个核壳镍纳米粒子内绘制三维应变异质性。我们报告了晶体核心镍区域内均匀位移和应变的直接观察。我们确定了核-壳界面以及纳米级外壳内的不均匀位移和位错形态。通过跟踪外壳区域中的单个位错线，并比较Burgers矢量和位错线之间的相对方向，我们确定了全部和部分位错。完全位错与位错附近的弹性理论一致，而部分位错则偏离该理论。我们利用原子计算和Landau-Lifshitz-Gilbert模拟以及密度泛函理论来确认粒子的平衡形状和从布拉格相干衍射成像（BCDI）实验获得的（111）位移场的性质。Ni纳米粒子的芯区域内的这种位移场分布在芯区域内提供了均匀的磁化分布。我们观察到，核心区域内不存在位错与磁化投影的均匀分布相关。我们的发现表明，使用BCDI进行缺陷成像对于巨型磁阻设备（例如硬盘驱动器读头）可能非常重要，其中位错的存在会影响磁畴壁的钉扎和矫顽力。