Additive manufacturing meets thermomagnetic heat recovery: NiMn-based Heusler composites

Over 70% of global primary energy is lost as waste heat, with nearly half of these losses occurring below 100°C, a largely untapped resource for sustainable energy conversion. Thermomagnetic (TM) technologies offer a promising route to exploit this low-grade heat, yet their scalability has been hindered by limitations in materials processing and device design. Here, we introduce an additive manufacturing (AM) strategy to fabricate TM composite rotors, embedding NiMn-based Heusler alloys into polymeric filaments via a simple capsule-filling method. The resulting FDM-compatible filaments were printed into thin, mechanically robust rotors that preserve the intrinsic Curie transitions of the active powders. In-operando testing in a Curie-wheel prototype demonstrates clear TM responses, with Ni₄₈Mn₃₆In₁₆-based rotors delivering up to 55% higher power output than Ni₄₈Mn₃₆Sn₁₆ counterparts. A systematic study of rotor thickness further reveals a ∼5% enhancement in performance for thinner geometries, highlighting the decisive role of surface-to-volume ratio in thermal exchange efficiency. This work establishes the first successful realization of 3D-printed TM rotors for energy harvesting, demonstrating that AM can precisely tailor geometry and material distribution to create lightweight, high-surface-area components optimized for low-grade waste heat recovery.