Synthesis of hard/soft magnetically exchange-coupled heterostructures is one promising way to design
energy-efficient rare-earth-free artificial magnetic materials for application as permanent magnets and in
spintronics. As a model system, we experimentally investigate MnGa/FeCo bilayers and simulate their physical behavior in a combined density functional theory and micromagnetic approach. Using highquality
L10 -Mn1.5 Ga thin films with bulklike magnetic properties, we show that optimal coherent exchange
coupling is obtained below a critical soft magnetic layer thickness that depends on the interface structure
and composition. In particular, for atomically smooth and matched epitaxial interfaces of L10 -Mn1.5 Ga
to a Co-terminated and Co-rich FeCo layer, coherent exchange coupling is observed for FeCo thicknesses
below 2 nm. In optimized bilayers, the magnetic coercivity of MnGa (approximately 6 kOe) can be fully conserved while the overall saturation magnetization is increased beyond 1000 emu/cm. Our model correlates interface structure and magnetic exchange coupling, providing guidelines to engineer high-performance exchange-coupled heterostructures for permanent magnets or spintronic devices.