Issue 30, 2020

Elucidating the role of shape anisotropy in faceted magnetic nanoparticles using biogenic magnetosomes as a model

Abstract

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.

Graphical abstract: Elucidating the role of shape anisotropy in faceted magnetic nanoparticles using biogenic magnetosomes as a model

Supplementary files

Article information

Article type
Paper
Submitted
18 Mar 2020
Accepted
29 Apr 2020
First published
02 Jul 2020
This article is Open Access
Creative Commons BY-NC license

Nanoscale, 2020,12, 16081-16090

Elucidating the role of shape anisotropy in faceted magnetic nanoparticles using biogenic magnetosomes as a model

D. Gandia, L. Gandarias, L. Marcano, I. Orue, D. Gil-Cartón, J. Alonso, A. García-Arribas, A. Muela and M. L. Fdez-Gubieda, Nanoscale, 2020, 12, 16081 DOI: 10.1039/D0NR02189J

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