Lattice-site-specific spin-dynamics in double perovskite Sr2CoOsO6

Original · EN

We have studied the magnetic properties and spin-dynamics of the structurally-ordered double perovskite Sr₂CoOsO₆. Our neutron diffraction, muon spin relaxation and ac-susceptibility measurements reveal two antiferromagnetic (AFM) phases on cooling from room temperature down to 2 K. In the first AFM phase, with transition temperature Tₙ=108 K, cobalt (3d⁷, S=3/2) and osmium (5d², S=1) moments fluctuate dynamically, while their average effective moments undergo long-range order. In the second AFM phase with Tₙ=67 K, cobalt moments first become frozen and induce a noncollinear spin-canted AFM state, while dynamically fluctuating osmium moments are later frozen into a randomly canted state at T≈ 5 K. Our ab initio calculations indicate that the effective exchange coupling between cobalt and osmium sites is rather weak, so that cobalt and osmium sublattices exhibit different ground states and spin-dynamics, making Sr₂CoOsO₆ distinct from previously reported double-perovskite compounds.