![Author ORCID: We display the ORCID iD icon alongside authors names on our website to acknowledge that the ORCiD has been authenticated when entered by the user. To view the users ORCiD record click the icon. [opens in a new tab]](https://chemrxiv.org/engage/assets/public/chemrxiv/images/logos/orcid.png)
Abstract
Composition is a key parameter to effectively tune the magnetic anisotropy of magnetic nanoparticles, which in turn can modulate their structural-magnetic properties and, thus,their final applications. The Mn2+ content of manganese ferrite nanoparticles (MnxFe3-xO4) deeply impacts their structure, magnetism, and, thus, their capacity as nanoheaters. To properly unveil how Mn2+ content influences these parameters, it is essential to synthesize monodisperse MNPs with similar sizes and shapes. Herein we report the synthesis of a wide range of MnxFe3-xO4 with x = 0.14 to 1.40, with similar polyhedral morphologies and sizes (13 to 15 nm) to exclude the crucial role that size and shape play. We demonstrate that high Mn2+ levels (x ≥ 0.70) lead to structural changes and the appearance of strain defects reflected in their poor saturation magnetization (Ms) values but, without modification of the final crystallite size. For the rest of the samples (in the range of x = 0.0 up to 0.70), average Ms values remain nearly constant despite Mn2+ levels, but the coercive field (Hc) varies significantly, indicating the critical role of composition in driving the transition of the particles towards soft magnets behaviors. As MNPs were synthesized in organic solvents, they were transferred into water using a polymer coating. Even when this step is often overlooked, water transference results in cations leaching, promoting vacancies and changes in the local ferrite structure. These changes had a minor impact on Ms values, suggesting that leaching probably affects the cations located closer to the surface. The magnetic heating capabilities were evaluated by calorimetry and AC magnetometry, finding that the heating capacity increased as the Mn2+ content increased (x ≤ 0.60). Lastly, selected MNPs (x = 0.07 and 0.60) were incubated with MIA PaCa-2 cell line for 24 h, showing an absence of cell cytotoxicity together with a high internalization rate independent of the compositions used. Our detailed analysis provides a better understanding of the effect of composition on the efficiency of heat generation and straightforward guidance for the optimized composition needed to modulate structural-magnetic properties depending on the final applications.
