Nanoscale Mapping of Heterogeneous Strain and Defects in Individual Magnetic Nanocrystals

Abstract

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.

Bragg Coherent Diffraction Imaging for In Situ Studies in Electrocatalysis

“…BCDI has been applied in several fields of science and technology including the study of NPs in general, ,,,,,− zeolites, , heterogeneous catalysis, ,,− batteries, − supercapacitors dielectrics, − nanowires, ,− minerals, − alloys and dealloying, − nanorods, ,− proteins, − thin films, ,…”

Imaging defects in vanadium(iii) oxide nanocrystals using Bragg coherent diffractive imaging

“…This recovered phase contains information about distortions to the crystal lattice in the direction normal to the diffracting planes. BCDI has been used extensively to map Bragg electronic density, displacement, ferroelectric domains and strain within the volume of crystals with nanoscale resolution; [18][19][20][21][22][23][24][25] the best reported resolution to date is 4-9nm. 26 It has been shown that BCDI can detect signatures of defects by measuring the disruptions to the long-range order of the crystal.…”