Interplay Between Structure and Interfacial Interactions in Fe‐Gd Synthetic Ferrimagnets

ABSTRACT Transition metal–rare earth compounds are promising synthetic ferrimagnets for next‐generation spintronic devices, where magnetic domain structure and thermal evolution are key to performance. We studied ultrathin Fe–Gd ferrimagnets grown epitaxially on W(110) by atomic layer deposition, combining element‐resolved magnetic microscopy with structural characterization. Comparing Gd/Fe and Fe/Gd bilayers with homogeneous Fe 1 − x Gd x alloys, we find that Curie temperature ( T c ) and domain behavior are governed primarily by crystallinity and interfacial coupling. In crystalline Gd/Fe, the Gd layer remains ferromagnetic up to ∼500 K, far above its bulk T c , due to strong interfacial coupling. In contrast, poor crystallinity of the Fe layer in Fe/Gd suppresses Fe magnetic order, yielding a reduced common T c of ∼325 K, similar to the homogeneous alloy ( T c ∼ 345 K). Atomistic spin simulations capture these trends and isolate the role of disorder. Together, these results demonstrate how structural control can be used to tune Curie and compensation temperatures in ultrathin ferrimagnetic heterostructures for ultrafast, energy‐efficient spintronic applications.