Functionally graded magnetocaloric elastomer via rheological modulation

Polymer-bonded magnetocaloric composites offer a solution to the intrinsic brittleness of Heusler alloys, yet conventional homogeneous architectures fail to optimize thermodynamic efficiency for regenerative cooling cycles. Here, we report the fabrication of a functionally graded magnetocaloric elastomer (FG-MCE) via a single-step, rheological modulated sedimentation strategy. By balancing Stokesian settling kinetics against the crosslinking of a polydimethylsiloxane (PDMS) matrix, we stabilized a continuous compositional gradient ranging up to 39 wt.% along the gravitational axis. X-ray micro-tomography confirms distinct architectural zones. Crucially, magnetic characterization reveals that the milling-induced microstructural refinement effectively stabilizes second-order thermomagnetic transition across the operating range. This modification eliminates the detrimental thermal hysteresis typical of Heusler alloys and overcomes the volume expansion that leads to composite failure. By normalizing the entropy change to the active mass, we further confirm that the soft elastomeric matrix acts as a compliant binder, preserving the intrinsic magnetocaloric performance. Consequently, this density-mediated assembly offers a scalable route to tailor the local magnetocaloric power density, a critical requirement for next-generation active magnetic regenerator elements.