Two-Dimensional Altermagnetic Iron Oxyhalides: Real Chern Topology and Valley–Spin–Lattice Coupling

Altermagnets, a novel class of collinear magnetic materials,
exhibit
unique spin-split band structures, yet topological insulating states
in intrinsic altermagnetic systems are rare. Here, we identify monolayer
Fe2X2O (X = Cl, Br, I) as a new family of 2D
altermagnetic real Chern insulators. These materials display robust d-wave altermagnetic ordering, semiconducting band gaps,
and nontrivial real Chern numbers per spin channel, yielding spin-polarized
topological corner modes. They also feature spin-polarized valleys
with strong altermagnetism–valley–spin–lattice
coupling, enabling valley-selective excitation via linear dichroism
and strain-induced valley polarization. In multiferroic Fe2Cl2O, magnetism coexists with ferroelasticity, and an
applied strain can switch the Néel vector. These findings position
2D iron oxyhalides as a promising platform for exploring the altermagnetism
and magnetic topological states for spintronics and valleytronics.