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Elucidating the role of shape anisotropy in faceted magnetic nanoparticles using biogenic magnetosomes as a model.
Nanoscale ( IF 5.8 ) Pub Date : 2020-07-02 , DOI: 10.1039/d0nr02189j David Gandia 1 , Lucía Gandarias 2 , Lourdes Marcano 3 , Iñaki Orue 4 , David Gil-Cartón 5 , Javier Alonso 6 , Alfredo García-Arribas 7 , Alicia Muela 8 , Mª Luisa Fdez-Gubieda 7
Nanoscale ( IF 5.8 ) Pub Date : 2020-07-02 , DOI: 10.1039/d0nr02189j David Gandia 1 , Lucía Gandarias 2 , Lourdes Marcano 3 , Iñaki Orue 4 , David Gil-Cartón 5 , Javier Alonso 6 , Alfredo García-Arribas 7 , Alicia Muela 8 , Mª Luisa Fdez-Gubieda 7
Affiliation
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Shape anisotropy is of primary importance to understand the magnetic behavior of nanoparticles, but a rigorous analysis in polyhedral morphologies is missing. In this work, a model based on finite element techniques has been developed to calculate the shape anisotropy energy landscape for cubic, octahedral, and truncated-octahedral morphologies. In all cases, a cubic shape anisotropy is found that evolves to quasi-uniaxial anisotropy when the nanoparticle is elongated ≥2%. This model is tested on magnetosomes, ∼45 nm truncated octahedral magnetite nanoparticles forming a chain inside Magnetospirillum gryphiswaldense MSR-1 bacteria. This chain presents a slightly bent helical configuration due to a 20° tilting of the magnetic moment of each magnetosome out of chain axis. Electron cryotomography images reveal that these magnetosomes are not ideal truncated-octahedrons but present ≈7.5% extrusion of one of the {001} square faces and ≈10% extrusion of an adjacent {111} hexagonal face. Our model shows that this deformation gives rise to a quasi-uniaxial shape anisotropy, a result of the combination of a uniaxial (Ksh–u = 7 kJ m−3) and a cubic (Ksh–c = 1.5 kJ m−3) contribution, which is responsible for the 20° tilting of the magnetic moment. Finally, our results have allowed us to accurately reproduce, within the framework of the Landau–Lifshitz–Gilbert model, the experimental AC loops measured for these magnetotactic bacteria.
中文翻译：
阐明形状各向异性在刻面磁性纳米粒子中的作用，并以生物体磁小体为模型。
形状各向异性对于理解纳米粒子的磁行为至关重要，但是缺少对多面体形态的严格分析。在这项工作中，已经开发了基于有限元技术的模型来计算立方，八面体和截头八面体形态的形状各向异性能态。在所有情况下，均会发现立方各向异性，当纳米粒子伸长≥2％时，该各向异性将演变为准单轴各向异性。该模型在磁小体上进行了测试，磁小体约45 nm截短的八面体磁铁矿纳米颗粒在Magnetospirillum gryphiswaldense内部形成链MSR-1细菌。由于每个磁小体的磁矩从链轴倾斜20°，因此该链呈现出略微弯曲的螺旋结构。电子冷冻断层扫描图像显示，这些磁小体不是理想的截短八面体，但{001}方形面之一的挤压强度约为7.5％，相邻{111}六角形面的挤压强度约为≈10％。我们的模型表明，这种变形会导致准单轴形状各向异性，这是单轴（K sh–u = 7 kJ m -3）和立方（K sh–c = 1.5 kJ m -3）结合的结果）贡献，这是导致磁矩倾斜20°的原因。最后，我们的结果使我们能够在Landau–Lifshitz–Gilbert模型的框架内准确地再现针对这些趋磁细菌测得的实验性AC回路。
更新日期：2020-08-06
中文翻译：
阐明形状各向异性在刻面磁性纳米粒子中的作用，并以生物体磁小体为模型。
形状各向异性对于理解纳米粒子的磁行为至关重要，但是缺少对多面体形态的严格分析。在这项工作中，已经开发了基于有限元技术的模型来计算立方，八面体和截头八面体形态的形状各向异性能态。在所有情况下，均会发现立方各向异性，当纳米粒子伸长≥2％时，该各向异性将演变为准单轴各向异性。该模型在磁小体上进行了测试，磁小体约45 nm截短的八面体磁铁矿纳米颗粒在Magnetospirillum gryphiswaldense内部形成链MSR-1细菌。由于每个磁小体的磁矩从链轴倾斜20°，因此该链呈现出略微弯曲的螺旋结构。电子冷冻断层扫描图像显示，这些磁小体不是理想的截短八面体，但{001}方形面之一的挤压强度约为7.5％，相邻{111}六角形面的挤压强度约为≈10％。我们的模型表明，这种变形会导致准单轴形状各向异性，这是单轴（K sh–u = 7 kJ m -3）和立方（K sh–c = 1.5 kJ m -3）结合的结果）贡献，这是导致磁矩倾斜20°的原因。最后，我们的结果使我们能够在Landau–Lifshitz–Gilbert模型的框架内准确地再现针对这些趋磁细菌测得的实验性AC回路。
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