Designing well-defined magnetic nanomaterials is crucial for various applications, and it demands a comprehensive understanding of their magnetic properties at the microscopic level. In this study, we investigate the contributions to the total anisotropy of Mn/Co mixed spinel nanoparticles. By employing neutron measurements sensitive to the spatially resolved surface anisotropy with sub-Å space resolution, we reveal an additional contribution to the anisotropy constant arising from shape anisotropy and interparticle interactions. Our findings shed light on the intricate interplay among chemical composition, microstructure, morphology, and surface effects, providing valuable insights for the design of advanced magnetic nanomaterials for AC biomedical applications, such as cancer treatment by magnetic fluid hyperthermia.

Department of Chemical and Geological Sciences University of Cagliari S S 554 Bivio per Sestu 09042 8 Monserrato CA Italy

Department of Inorganic Chemistry Charles University Hlavova 2030 8 128 43 Prague 2 Czech Republic

Department of Physical and Macromolecular Chemistry Charles University Hlavova 2030 8 128 43 Prague 2 Czech Republic

Dipartimento di Chimica and INSTM Universita'di Firenze Via della Lastruccia 3 1 50019 Sesto Fiorentino Italy

Institute of Physics Faculty of Science P J Šafárik University Park Angelinum 9 04001 Košice Slovakia

ISIS Neutron and Muon Facility Science and Technology Facilities Council Rutherford Appleton Laboratory OX11 0QX Didcot U K

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