Magnetically driven loss of centrosymmetry in metallic Pb_2CoOsO_6

摘要

We report magnetic, transport, neutron diffraction, and muon spin rotation data showing that Pb_2CoOsO_6, a metallic double-perovskite with a centrosymmetric space group at room temperature exhibits a continuous second-order phase transition at 45 K to a magnetically ordered state with a noncentrosymmetric space group. The absence of inversion symmetry is very uncommon in metals, particularly metallic oxides. In contrast to the recently reported ferroelectriclike structural transition in LiOsO_3, the phase transition in Pb_2CoOsO_6 is driven by a long-range collinear antiferromagnetic order, with propagation vector k = (1/2, 0, 1/2), which relieves the frustration associated with the symmetry of the magnetic exchanges. This magnetically driven loss of inversion symmetry represents another frontier in the search for novel metallic behavior.