Thermal stability and structural ordering of thick Co₂MnAl films grown on MgO and Si substrates

While most studies on Co 2 MnAl (CMA) focus on the ultrathin regime for spintronic junctions, applications scaling with magnetic volume—such as Anomalous Nernst Effect (ANE) energy harvesters, integrated power inductors, and magnetic MEMS—require significantly thicker films. In this work, 750 nm thick CMA films were grown on MgO (001) and Si substrates to establish a roadmap for their thermal integration. Structural analysis reveals that B2 ordering is optimized on MgO at 600°C, which is important for functional devices. In contrast, samples on Si substrates exhibit a disorder transition toward the A2 phase, closely linked to diffusion‑driven degradation processes. Above 500°C, Si interdiffusion into the Heusler layer triggers the formation of interfacial silicides and Kirkendall voids, leading to microcracking, electrical resistivity jumps, and a final fully disordered A2 phase. Despite the Mn-poor stoichiometry (Co 2.25 Mn 0.7 Al 1.05 ), the films maintain a robust saturation magnetization of ~600 emu/cm³. These results define the processing windows for integrating thick CMA layers into multifunctional CMOS-compatible platforms.