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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.

 Fuente: Nanoscale, 2020,12, 16081-16090

Editorial: Royal Society of Chemistry

 Año de publicación: 2020

Nº de páginas: 10

Tipo de publicación: Artículo de Revista

DOI: 10.1039/D0NR02189J

ISSN: 2040-3364,2040-3372

Proyecto español: MAT2017- 83631-C3

Url de la publicación: https://doi.org/10.1039/D0NR02189J

Autores/as

GANDIA, DAVID

GANDARIAS, LUCÍA

MARCANO, LOURDES

ORUE, IÑAKI

GIL-CARTÓN, DAVID

ALFREDO GARCIA ARRIBAS

MUELA, ALICIA

MARIA LUISA FERNANDEZ-GUBIEDA RUIZ