Microstructural engineering represents a promising avenue toward controlling the macroscopic response of high-performance magnetic materials, yet the physical origins linking microstructure to magnetic properties remain to be fully established. In this contribution, we establish magnetoplastic control over macroscopic magnetic properties by inducing high densities of extended lattice defects within the prototypical $L{2}_1$-ordered intermetallic ${\mathrm{MnCu}}_2\mathrm{Al}$, which serves as an ideal model system. We demonstrate a nearly 95% decrease in the initial net saturation magnetization following a high degree of plastic deformation, with effects that are reversible through annealing. Synchrotron X-ray diffraction and scanning electron nanodiffraction permit microscopic correlation of the changes in magnetic behavior with increasing defect content. Microstructural characterization at the single defect level, coupled with detailed first-principles modeling, suggests the presence of a local antiferromagnetic coupling within the extended defects that is at the origin of the dramatic magnetoplastic effect in these magnetic intermetallics. We ascribe these effects to the planar dissociation of dislocations hosting intervening antiphase boundaries, altering the atomic environment and, in turn, the magnetic coupling in the vicinity of dislocations.

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• Magnetic coupling
• Magnetism
• Mechanical deformation
• Plasticity