Independent Ordering of Two Interpenetrating Magnetic Sublattices in the Double Perovskite Sr₂CoOsO₆

Abstract

The insulating, fully ordered, double perovskite Sr2CoOsO6 undergoes two magnetic phase transitions. The Os(VI) ions order antiferromagnetically with a propagation vector k = (1/2, 1/2, 0) below TN1 = 108 K, while the high-spin Co(II) ions order antiferromagnetically with a propagation vector k = (1/2, 0, 1/2) below TN2 = 70 K. Ordering of the Os(VI) spins is accompanied by a structural distortion from tetragonal I4/m symmetry to monoclinic I2/m symmetry, which reduces the frustration of the face centered cubic lattice of Os(VI) ions. Density functional theory calculations show that the long-range Os-O-Co-O-Os and Co-O-Os-O-Co superexchange interactions are considerably stronger than the shorter Os-O-Co interactions. The poor energetic overlap between the 3d orbitals of Co and the 5d orbitals of Os appears to be responsible for this unusual inversion in the strength of short and long-range superexchange interactions.

Lattice-Site-Specific Spin Dynamics in Double PerovskiteSr2CoOsO6

“…This contrasts with the spin configurations presented in Ref. [24] where the proposed AFM order below 70 K appears incompatible with the glassiness we observe.…”

“…suggested in Ref. [24] that the cobalt moments align within the ac plane. However, an interpretation that is more consistent with our data from other techniques (discussed below) is obtained if the moments in the AF1 phase align within the ab plane and an additional ordering in AF2 0 occurs along c. At 2 K the c component of the Co moment reaches a value of μ c;k 2 ðCoÞ ¼ 2.1ð1Þ μ B , resulting finally in a total magnetic moment μ tot ðCoÞ ¼ 2.6ð1Þ μ B via a vector sum over its ab and c components.…”

Effects of chemical pressure on the magnetic ground states of the osmate double perovskitesSrCaCoOsO6andCa2CoOsMorrow1, Yan2, McGuire3 et al. 2015Phys. Rev. BSelf Cite387410View full textAdd to dashboardCite

“…PbO 2 was included separately as an in-situ oxygen gas source as described in an earlier study [11]. Further synthetic details and precautions are elaborated in Ref.…”

“…When the B−O−B′ superexchange is strong, as is the case for Sr 2 CrOsO 6 (T C = 725 K), high temperature ferrimagnetism is observed [10]. When it is very weak, as is the case for Sr 2 CoOsO 6 , AFM ordering of weakly coupled B and B′ sublattices results [11,12]. When the B−O−B′ interaction is intermediate between these two extremes, highly frustrated magnetic ground states and incommensurate magnetic order are expected to emerge.…”

Magnetic order and electronic structure of the5d3double perovskiteSr2ScOsO6

“…2 [13,29]. The occupancies determined from XRPD were subsequently used in the NPD structural refinements.…”