  Permanent magnets draw their properties from a complex interplay, across
multiple length scales, of the composition and distribution of their
constituting phases, that act as building blocks, each with their associated
intrinsic properties. Gaining a fundamental understanding of these interactions
is hence key to decipher the origins of their magnetic performance and
facilitate the engineering of better-performing magnets, through unlocking the
design of the "perfect defects" for ultimate pinning of magnetic domains. Here,
we deployed advanced multiscale microscopy and microanalysis on a bulk
Sm2(CoFeCuZr)17 pinning-type high-performance magnet with outstanding thermal
and chemical stability. Making use of regions with different chemical
compositions, we showcase how both a change in the composition and distribution
of copper, along with the atomic arrangements enforce the pinning of magnetic
domains, as imaged by nanoscale magnetic induction mapping. Micromagnetic
simulations bridge the scales to provide an understanding of how these
peculiarities of micro- and nanostructure change the hard magnetic behaviour of
Sm2(CoFeCuZr)17 magnets. Unveiling the origins of the reduced coercivity allows
us to propose an atomic-scale defect and chemistry manipulation strategy to
define ways toward future hard magnets.
