Symmetry-breaking induced surface magnetization in nonmagnetic RuO2

Altermagnetism, a collinear magnetic phase distinct from ferro- and antiferromagnetism, has drawn attention with RuO₂ as a leading candidate. While theory predicted sizable Ru local moments driving antiferromagnetic order, a growing pile of experiments suggests that the bulk is essentially nonmagnetic, consistent with delocalized 4$d$ electrons and metallic screening. In this study, the authors reveal that the RuO₂(110) surface breaks this trend: symmetry breaking at the surface induces electronic redistribution and spontaneous magnetization. This surface magnetism produces spin-polarized states, distinctive scanning probe signatures, and potential spin-dependent transport, underscoring how subtle surface effects can radically alter the magnetic character of a nominally nonmagnetic material.