Origin of magnetic excitation gap in double perovskite 
<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msub><mml:mi>Sr</mml:mi><mml:mn>2</mml:mn></mml:msub><mml:msub><mml:mi>FeOsO</mml:mi><mml:mn>6</mml:mn></mml:msub></mml:mrow></mml:math>

Taylor, Arthur J.; Morrow, Ryan; Lumsden, M. D.; Calder, Stuart; Upton, M. H.; Kolesnikov, A. I.; Stone, M. B.; Fishman, Randy; Paramekanti, Arun; Woodward, Patrick M.; Christianson, A. D.

doi:10.1103/physrevb.98.214422

Cited by 19 publications

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References 32 publications

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“…However, if intersite exchange competes with SOC, it can lead to magnetic ordering from exciton condensation [22,27]; clear experimental candidates for such an exciton condensate are yet to be found. Further down, a d 3 configuration would naively be expected to form an orbital singlet state with spin S = 3/2; however, neutron scattering and resonant inelastic X-ray scattering experiments have found that 5d transition metal oxides bely this expectation, finding magnetically ordered states with large spin gaps which clearly reveal the dominance of SOC over Hund's coupling [28][29][30]. Skipping to d 1 ions, we are led to a j eff = 3/2 angular momentum state.…”

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confidence: 99%

Octupolar order in d -orbital Mott insulators

2020

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Motivated by experimental and theoretical interest in realizing multipolar orders in d-orbital materials, we discuss the quantum magnetism of J = 2 ions on the face-centered cubic lattice which can be realized in spin-orbit coupled oxides with 5d 2 transition metal ions. Based on the crystal field environment, we argue for a splitting of the J = 2 multiplet, leading to a low lying non-Kramers doublet which hosts quadrupolar and octupolar moments. We discuss a microscopic mechanism whereby the combined perturbative effects of orbital repulsion and antiferromagnetic Heisenberg spin interactions leads to ferro-octupolar coupling between neighboring sites, and stabilizes ferrooctupolar order. This same mechanism is also shown to disfavor quadrupolar ordering. We study spin dynamics in the ferro-octupolar state using a slave-boson approach, uncovering a gapped and dispersive magnetic exciton. For sufficiently strong magnetic exchange, the dispersive exciton can condense, leading to conventional type-I antiferromagnetic order which can preempt octupolar order. Our proposal for ferrooctupolar order, with specific results in the context of a model Hamiltonian, provides a comprehensive understanding of thermodynamics, µSR, X-ray diffraction, and inelastic neutron scattering measurements on a range of cubic 5d 2 double perovskite materials including Ba2ZnOsO6, Ba2CaOsO6, and Ba2MgOsO6. Our proposal for exciton condensation leading to type-I magnetic ordering is argued to be relevant to materials such as Sr2MgOsO6.PACS numbers: 75.25.aj, 75.40.Gb, 75.70.Tj Multipolar symmetry-breaking orders have been extensively discussed in f -orbital based lanthanide and actinide compounds, which host ions where spin-orbit coupling (SOC) is a dominant energy scale [1]. For instance, the "hidden order" state of URu 2 Si 2 has been proposed to host hexadecapolar symmetry breaking [2]. Another well-known example is cubic NpO 2 [3-6], where a large body of experiments have been reconciled in terms of a primary antiferro-triakontadipolar (rank-5 magnetic multipolar) symmetry breaking which drives secondary antiferro-quadrupolar order. In certain pyrochlore magnets, all-in all-out magnetic order has been proposed to lead to "effective octupoles" on tetrahedra [7]. Ongoing experimental [8-10] and theoretical investigations [11][12][13][14] of PrTi 2 Al 20 and PrV 2 Al 20 have also uncovered quadrupolar and ferro-octupolar orders.Recently, unconventional multipolar orders have also been proposed in d-orbital metals to occur as Pomeranchuk instabilities of spin-orbit coupled Fermi surfaces [15]. Specifically, metallic oxides which have d-orbital ions with large SOC, such as LiOsO 3 and Cd 2 Re 2 O 7 , have been proposed as potential candidates to realize this physics [15]. Experiments have indeed discovered an oddparity nematic metal in Cd 2 Re 2 O 7 below T c ∼ 200 K via optical second-harmonic generation [16]. Other proposed materials for hosting multipolar orders include A 2 OsO 4 (with A = K,Rb,Cs) [17].However, to the best of our knowledg...

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Octupolar order in d -orbital Mott insulators

2020

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“…Moreover, the magnitudes of J H and ζ are consistent with values obtained for other 5d systems. 35,[42][43][44] The fact that the values we obtain are significantly smaller than the free ion limit (ζ 5d = 0.50 eV and J H = 3B + C = 0.44 eV from Ref. 45) is characteristic of a significant nephelauxetic (orbital expanding) effect.…”

Section: A Ligand Field Theory Calculationsmentioning

confidence: 53%

Spin and orbital excitations through the metal-to-insulator transition in Cd2Os2O7 probed with high-resolution resonant inelastic x-ray scattering

et al. 2020

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High-resolution resonant inelastic x-ray scattering measurements (∆E = 46 meV) have been performed on Cd2Os2O7 through the metal-to-insulator transition (MIT). A weakly dispersive magnetic excitation at 120 meV evolves continuously through the MIT, in agreement with recent Raman scattering results, and provides further confirmation for an all-in, all-out magnetic ground state. Asymmetry of this feature is likely a result of coupling between the electronic and magnetic degrees of freedom. We also find that the orbital excitations exhibit a degree of 5d 4 character, which differs from the nominal 5d 3 . This has been verified by semiempirical ligand field theory and ab initio quantum chemistry calculations. We explore the possible origins for this behavior, including the possibility that the free ion model breaks down for Cd2Os2O7.

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“…On the other hand, the heat capacity study on the cubic Ba2DyRuO6 reveals only a single anomaly at 47 K [48], similar to La2NaRuO6 [11,41]. Further, Sr2FeOsO6 exhibits two magnetic transitions at TN1=140 K and TN2=67 K, where both the Fe and Os moments order and the second transition is associated with the change in magnetic structure from AF1 to AF2 [49]. Considering the observation of a spin gap only below TN2 in the inelastic study of Sr2FeOsO6, it was suggested that spin-orbit coupling is important for ground state selection in this compound [49].…”

Section: (B) Physical Propertiesmentioning

confidence: 93%

Muon spin rotation and neutron scattering investigations of the B -site ordered double perovskite Sr2DyRuO6

et al. 2020

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The magnetic ground state of B-site ordered double perovskite Sr2DyRuO6 has been investigated using muon spin rotation and relaxation (µSR), neutron powder diffraction (NPD) and inelastic neutron scattering (INS), in addition to heat capacity and magnetic susceptibility (ac and dc) measurements. A clear signature of a long-range ordered magnetic ground state has been observed in the heat capacity data, which exhibit two sharp anomalies at 39.5 and 36 K found as well in the magnetic data. Further confirmation of long-range magnetic ordering comes from a sharp drop in the muon initial asymmetry and a peak in the relaxation rate at 40 K, along with a weak anomaly near 36 K. Based on temperature dependent NPD, the low temperature magnetic structure contains two interpenetrating lattices of Dy 3+ and Ru 5+ , forming an antiferromagnetic ground state below 39.5 K with magnetic propagation vector k = (0,0,0). The magnetic moments of Dy 3+ and Ru 5+ at 3.5 K are pointing along the crystallographic b-axis with values of µ Dy = 4.92(10) µB and µ Ru = 1.94(7) µB, respectively. The temperature dependence of the Ru 5+ moments follows a mean field type behaviour, while that of the Dy 3+ moments exhibits a deviation indicating that the primary magnetic ordering is induced by the order of the 4d-electrons of Ru 5+ rather than that of its proper 4f-Dy 3+ electrons. The origin of the second anomaly observed in the heat capacity data at 36.5 K must be connected to a very small spin reorientation as the NPD studies do not reveal any clear change in the observed magnetic Bragg peaks' positions or intensities between these two transitions. INS measurements reveal the presence of crystal field excitations (CEF) in the paramagnetic state with overall CEF splitting of 73.8 meV, in agreement with the point change model calculations, and spin wave excitations below 9 meV at 7 K. Above TN, the spin wave excitations transform into a broad diffuse scattering indicating the presence of short-range dynamic magnetic correlations.

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Origin of magnetic excitation gap in double perovskite Sr2FeOsO6

Cited by 19 publications

References 32 publications

Octupolar order in d -orbital Mott insulators

Octupolar order in d -orbital Mott insulators

Spin and orbital excitations through the metal-to-insulator transition in Cd2Os2O7 probed with high-resolution resonant inelastic x-ray scattering

Muon spin rotation and neutron scattering investigations of the B -site ordered double perovskite Sr2DyRuO6

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