Agradecimentos: The Article Processing Charge for the publication of this research was funded by the Coordination for the Improvement of Higher Education Personnel - CAPES (ROR identifier: 00x0ma614). This study was mainly supported and performed under the auspices of the São Paulo research foundation (FAPESP) through Grant no. 2017/10581-1 and 2022/16460-0, CNPq 303227/2020-6, and 305057/2023-5. A.A.d.A. is the beneficiary of a postdoctoral FAPESP fellowship Grant no. 2021/13592-0. Futhermore, F.F. is the beneficiary of a postdoctoral FAPESP fellowship Grant no. 2019/13678-1. This research used facilities of the Brazilian Nanotechnology National Laboratory (LNNano), part of the Brazilian Centre for Research in Energy and Materials (CNPEM), a private nonprofit organization under the supervision of the Brazilian Ministry for Science, Technology, and Innovations (MCTI). The electronic microscopy staff is acknowledged for the assistance during the experiments (proposal numbers: 20210585 and 20230533) Ver menos

Abstract: Magnetic hyperthermia (MH) has emerged as a promising technology with diverse applications in medical and technological fields, leveraging the remote induction of temperature elevation through an alternating magnetic field. While Fe3O4 nanoparticles with an average size around 12-25 nm are commonly employed in MH systems, this study introduces a strategy to produce smaller particles (less than or equal to 10 nm) with enhanced heating efficiency, as measured by specific power absorption (SPA). We conducted an exhaustive and detailed investigation into the morphological and magnetic properties of CoxFe3-xO4 nanoparticles, aiming to optimize their MH response. By varying the Co content, we successfully tuned the effective magnetic anisotropy while maintaining saturation magnetization nearly constant. The MH analysis indicates that these nanoparticles predominantly heat through the Neel mechanism, demonstrating robust reproducibility across different concentrations, viscosity mediums, and ac field conditions. Notably, we identified an optimal anisotropy or Co concentration that maximizes SPA, crucial for developing magnetic systems requiring particles with specific sizes. This work contributes to advancing the understanding and application of MH, particularly in tailoring nanoparticle properties for targeted and efficient heat generation in various contexts Ver menos