A common material used in electronics has been hiding a secret magnetic layer that only exists on its skin.
April 14, 2026
Original Paper
Surface ferrimagnetic order in RuO2 film
arXiv · 2604.10659
The Takeaway
RuO2 was at the center of a massive debate because some researchers saw magnetism while others didn't. This paper proves the bulk material is non-magnetic, but its surface possesses a spontaneous magnetic order, fundamentally changing how we use it in computer memory.
From the abstract
RuO2, widely proposed as a prototypical altermagnet, remains intensely debated with regard to its magnetic nature. Here, we demonstrate that RuO2 is non-magnetic in the bulk, but possesses a spontaneous surface ferrimagnetic order. Using spin- and angle-resolved photoemission spectroscopy, we directly detect a narrow surface state with identical spin polarizations at opposite momenta and at the Brillouin-zone center, incompatible with the spin texture of any altermagnetic order. First-principles