Preserved metallicity and tunable magnetism in Zr-based Janus MXenes

Janus MXenes provide a chemically asymmetric platform to tailor the properties of two-dimensional transition metal carbides. Here, we present a systematic first-principles study of the structural, electronic, mechanical, and magnetic properties of Janus ZrMCX₂ MXenes (M = Cr, Hf, Nb, Sc, Ti; X = F, Cl, S). All compositions exhibit negative formation energies and satisfy the Born stability criteria, supporting the energetic and mechanical stability of the Janus structures. In contrast to the metal-to-semiconductor transitions frequently reported for functionalized MXenes, we find that the metallic character is preserved in nearly all ZrMCX₂ systems, despite the strong chemical asymmetry introduced by the Janus configuration. Surface functionalization nevertheless plays a key role in modulating the electronic density near the Fermi level and strongly influences the magnetic and mechanical responses. Several compounds exhibit ferromagnetic or antiferromagnetic ground states, three display half-metallicity, and sizable magnetic anisotropy energies are obtained, with Néel temperatures exceeding room temperature in selected cases. Functionalization also enhances the elastic stiffness of the Janus structures. These results demonstrate that chemical asymmetry and surface termination provide effective control over magnetic and mechanical properties while maintaining a robust metallic framework, identifying Zr-based Janus MXenes as promising model systems for metallic and spin-dependent two-dimensional materials.