Bulk rutile RuO2 has long been considered a Pauli paramagnet. Here we report that RuO2 exhibits a hitherto undetected lattice distortion below approximately 900 K. The distortion is accompanied by antiferromagnetic order up to at least 300 K with a small room temperature magnetic moment of approximately 0.05 μB as evidenced by polarized neutron diffraction. Density functional theory plus U (DFT+U) calculations indicate that antiferromagnetism is favored even for small values of the Hubbard U of the order of 1 eV. The antiferromagnetism may be traced to a Fermi surface instability, lifting the band degeneracy imposed by the rutile crystal field. The combination of high N\'eel temperature and small itinerant moments make RuO2 unique among ruthenate compounds and among oxide materials in general.
@article{arxiv.1612.09589,
title = {Itinerant Antiferromagnetism in RuO$_{2}$},
author = {T. Berlijn and P. C. Snijders and O. Delaire and H. -D. Zhou and T. A. Maier and H. -B. Cao and S. -X. Chi and M. Matsuda and Y. Wang and M. R. Koehler and P. R. C. Kent and H. H. Weitering},
journal= {arXiv preprint arXiv:1612.09589},
year = {2017}
}