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