Browsing by Author "Koehler, MR"

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    Itinerant Antiferromagnetism in RuO$_{2}$
    (PRL, 2017-02-23) Berlijn, T; Snijders, PC; Delaire, O; Zhou, H-D; Maier, TA; Cao, H-B; Chi, S-X; Matsuda, M; Wang, Y; Koehler, MR; Kent, PRC; Weitering, HH
    Bulk rutile RuO$_2$ has long been considered a Pauli paramagnet. Here we report that RuO$_2$ 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 $\mu_B$ 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 RuO$_2$ unique among ruthenate compounds and among oxide materials in general.