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TT: Fachverband Tiefe Temperaturen

TT 100: Frustrated Magnets - Pyrochlore Oxides

TT 100.9: Talk

Thursday, March 15, 2018, 17:45–18:00, H 3005

Magnetic semimetallic state in pyrochlore ruthenate Cd₂Ru₂O₇ — •Marian Blankenhorn¹, Tomohiro Takayama², Jürgen Nuss², Robert Dinnebier², Alexander Yaresko², and Hidenori Takagi^1,2 — ¹University of Stuttgart, Stuttgart, Germany — ²Max Planck Institute for Solid State Research, Stuttgart, Germany

In pyrochlore oxides with the chemical composition A₂B₂O₇ strong geometrical frustration gives rise to interesting phenomena such as spin-ice behavior. Metallic pyrochlore oxides also show a variety of electronic phases including superconductivity in Cd₂Re₂O₇ and a metal-insulator transition (MIT) in Tl₂Ru₂O₇. While many Ru⁴⁺ pyrochlores have been intensively studied, only three Ru⁵⁺ pyrochlores, A₂Ru₂O₇ (A=Hg, Ca, Cd), are known so far. While Ca₂Ru₂O₇ remains metallic at low temperatures showing spin-glass behavior, Hg₂Ru₂O₇ undergoes a MIT at around 100 K. For Cd₂Ru₂O₇ the formation of a SDW was proposed based on a drop of magnetic susceptibility and an anomaly in resistivity but no detailed information is available. We obtained single crystals of Cd₂Ru₂O₇ by high pressure synthesis. Both magnetic susceptibility and resistivity exhibit a sharp drop at around 105 K. This transition accompanies a loss of carriers, indicating a low-carrier metallic state at low temperatures. The LDA + U band calculation suggests an antiferromagnetic semimetallic ground state with possibly all-in all-out magnetic order. We argue that Cd₂Ru₂O₇ displays a unique transition where magnetic order induces a coherent semimetallic state out of an incoherent paramagnetic bad-metal.