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Abstract:
Magnetic properties and spin dynamics have been studied for the
structurally ordered double perovskite Sr2CoOsO6. 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 T-N1 = 108 K,
cobalt (3d(7), S = 3/2) and osmium (5d(2), S = 1) moments fluctuate
dynamically, while their average effective moments undergo long-range
order. In the second AFM phase below T-N2 = 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 approximate to 5 K. 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.
