Abstract: Magnetotactic bacteriaMagnetospirillum gryphiswal-densesynthesize cubo-octahedral shaped magnetite nanoparticles,called magnetosomes, with a mean diameter of 40 nm. The highquality of the biosynthesized nanoparticles makes them suitable fornumerous applications infields like cancer therapy, among others.The magnetic properties of magnetite magnetosomes can betailored by doping them with transition metal elements, increasingtheir potential applications. In this work, we address the effect ofMn doping on the main properties of magnetosomes by thecombination of structural and magnetic characterization techni-ques. Energy-dispersive X-ray spectroscopy, X-ray absorption near-edge structure, and X-ray magnetic circular dichroism results reveala Mn dopant percentage of utmost 2.3%, where Mn cations are incorporated as a combination of Mn2+and Mn3+, preferablyoccupying tetrahedral and octahedral sites, respectively. Fe substitution by Mn notably alters the magnetic behavior of the dopedmagnetosomes. Theoretical modeling of the experimental hysteresis loops taken between 5 and 300 K with a modified Stoner?Wohlfarth approach highlights the different anisotropy contributions of the doped magnetosomes as a function of temperature. Incomparison with the undoped magnetosomes, Mn incorporation alters the magnetocrystalline anisotropy introducing a negative andlarger cubic anisotropy down to the Verwey transition, which appears shifted to lower temperature values as a consequence of Mndoping. On the other hand, Mn-doped magnetosomes show a decrease in the uniaxial anisotropy in the whole temperature range,most likely associated with a morphological modification of the Mn-doped magnetosomes.

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