Emergent Topological Magnons and Thermal Hall Effect in 2D Filling‐Enforced Fully Compensated Ferrimagnets

ABSTRACT Magnons in collinear magnets with vanishing net magnetization offer unique advantages for spin transport, including ultrafast dynamics and robustness against external magnetic fields. However, in most symmetry‐enforced collinear antiferromagnets, symmetry relations between opposite‐chirality magnon branches constrain the Berry curvature and suppress the magnon thermal Hall effect (MTHE). Here, by comprehensively surveying four types of collinear compensated magnets–conventional antiferromagnets, altermagnets, type IV magnets, and fully compensated ferrimagnets (fFIMs)–we demonstrate that fFIMs with zero net magnetization lift the symmetry linkages between opposite spin sublattices and, remarkably, give rise to complete chirality splitting and an intrinsic MTHE. Moreover, first‐principles calculations identify the // heterostructure as an experimentally feasible 2D filling‐enforced fFIM with a finite MTHE. Analyzes of the spin Chern number, Chern number, and edge states reveal a topological magnon insulator phase, together with a ferroelectrically switchable magnonic phase transition in the // heterostructure. These results establish fFIMs as a versatile platform for topological thermal transport, paving the way for nonvolatile and electrically reconfigurable topological spin‐caloritronic devices.