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 0.05μB 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 Néel temperature and small itinerant moments make RuO2 unique among ruthenate compounds and among oxide materials in general. In the final part of this talk, I will present some preliminary data of epitaxial RuO2 thin films where the antiferromagnetic correlations are expected to increase.
 T. Berlijn et al., PRL 118, 077201 (2017)
Hanno Weitering is a professor of physics at the University of Tennessee, Knoxville, working in the area of experimental condensed matter physics, with special emphasis on surfaces, interfaces, and ultrathin film materials. Prof. Weitering earned his PhD in 1991 from the University of Groningen in The Netherlands and completed a two year postdoc at the University of Pennsylvania under the direction of Prof. Ward Plummer before moving to Tennessee. Prof. Weitering’s research interests include correlated electron phenomena and electronic instabilities at surfaces, low-dimensional superconductivity, dilute magnetic semiconductors, and oxide heterostructures. He currently serves as Head of the Department of Physics and Astronomy, and as Deputy Director of the Joint Institute of Advanced Materials, which is a joint venture between the University of Tennessee and Oak Ridge National Laboratory. Prof. Weitering was elected Fellow of the American Physical Society in 2009.