biostudies-literatureVijayakumar JSwiss National Science FoundationUniversity of Basel | Swiss Nanoscience Institute (SNI)University of Basel | Swiss Nanoscience InstituteEC | Horizon 2020 Framework ProgrammeEC | Horizon 2020 Framework Programme (EU Framework Programme for Research and Innovation H2020)174https://www.ebi.ac.uk/biostudies/studies/S-EPMC9837083biostudies-literatureUnknown14(1)Understanding chemical reactivity and magnetism of 3d transition metal nanoparticles is of fundamental interest for applications in fields ranging from spintronics to catalysis. Here, we present an atomistic picture of the early stage of the oxidation mechanism and its impact on the magnetism of Co nanoparticles. Our experiments reveal a two-step process characterized by (i) the initial formation of small CoO crystallites across the nanoparticle surface, until their coalescence leads to structural completion of the oxide shell passivating the metallic core; (ii) progressive conversion of the CoO shell to Co₃O₄ and void formation due to the nanoscale Kirkendall effect. The Co nanoparticles remain highly reactive toward oxygen during phase (i), demonstrating the absenceNature communicationsAbsence of a pressure gap and atomistic mechanism of the oxidation of pure Co nanoparticles.PMC98370832000212002_153540153540823717810310200021_160186P1502160186Savchenko TMLumbeeck GVaz CAFNolting FBeche ABracher DMVerbeeck JVijayakumar JKleibert AVajda SfalseAbsence of a pressure gap and atomistic mechanism of the oxidation of pure Co nanoparticles.Understanding chemical reactivity and magnetism of 3d transition metal nanoparticles is of fundamental interest for applications in fields ranging from spintronics to catalysis. Here, we present an atomistic picture of the early stage of the oxidation mechanism and its impact on the magnetism of Co nanoparticles. Our experiments reveal a two-step process characterized by (i) the initial formation of small CoO crystallites across the nanoparticle surface, until their coalescence leads to structural completion of the oxide shell passivating the metallic core; (ii) progressive conversion of the CoO shell to Co₃O₄ and void formation due to the nanoscale Kirkendall effect. The Co nanoparticles remain highly reactive toward oxygen during phase (i), demonstrating the absence2023-01-01T00:00:00Z2023 Jan2026-03-17T15:47:31.862Z2025-04-04T20:32:55.793ZS-EPMC98370833663527610.1038/s41467-023-35846-0