The smallest of defects can create serious problems. Berkeley Lab scientists have now used one of the world’s most powerful electron microscopes to map the precise location and chemical type of 23,000 atoms in a nanoparticle made of iron and platinum. The 3D reconstruction reveals the arrangement of atoms in unprecedented detail, enabling the scientists to measure chemical order and disorder in individual grains, which sheds light on the material’s properties at the single-atom level. Insights gained from the particle’s structure could lead to new ways to improve its magnetic performance for use in high-density, next-generation hard drives. The work could help spot consistent flaws in nanoparticle products, which could be vital in health care.