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Summary of Collaborative Investigation – Na 5 ACu 4 (AsO 4 ) 4 Cl 2 (A = Rb, Cs)

Summary of Collaborative Investigation – Na 5 ACu 4 (AsO 4 ) 4 Cl 2 (A = Rb, Cs). Jeffrey Clayhold, Miami University, USA Shiou-Jyh Hwu, Clemson University, USA Raivo Stern & Toomas Rõõm, National Institute of Chemical Physics & Biophysics, Estonia

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Summary of Collaborative Investigation – Na 5 ACu 4 (AsO 4 ) 4 Cl 2 (A = Rb, Cs)

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  1. Summary of Collaborative Investigation – Na5ACu4(AsO4)4Cl2 (A = Rb, Cs) Jeffrey Clayhold, Miami University, USA Shiou-Jyh Hwu, Clemson University, USA Raivo Stern & Toomas Rõõm, National Institute of Chemical Physics & Biophysics, Estonia Sergei Zvyagin, Marcelo Jaime &Neil Harrison National High Magnetic Field Laboratory, USA

  2. CuII-As-O CuII-As-O CuII-As-O b ACl / Na6O8 ACl / Na6O8 Cu-As-O ACl/Na6O8 Cu-As-O Na5ACu4(AsO4)4Cl2 (A = Rb, Cs): A Composite Structure of Alternating Magnetic and Insulating Slabs Na5RbCu4(AsO4)4Cl2 (Fmmm, no. 69) a = 14.632(2) Å b = 18.872(2) Å c = 14.445(2) Å V = 3988.8(3) Å3 Z = 8

  3. O Cu As a Cl c a Tetrameric m-oxo [Cu4O12]16- Clusters Cu-O: 1.93-1.99Å Cu-Cl: 2.78Å Cu-O-Cu: 108.7o - 110.9o

  4. q = -86 K g = 1.97 100 010 101 Temperature-Dependent Magnetic Susceptibility and Specific Heat Measurements A second-order phase transition Clayhold, et al.Phys. Rev. B2002, 66, 052403.

  5. Field Dependent Specific Heat Measurements Specific heat per temperature unit (C/T) for H along b-axis Notice the peak (marking TN) shifting to lower temperatures as applied field grows

  6. Field Dependence of TN from Specific Heat and NMR Measurements Field dependence of the Neel temperature (TN) for low fields

  7. Na5RbCu4(AsO4)4Cl2: Tunable-Frequency Electron Spin Resonance Measurements • Direct observation of the gap in the AFM ordered phase • (Δ ~ 18 K) • (ii) Potential evidence of the “gigantic” Dzyaloshinskii-Moriya interaction Zvyagin, et al., unpublished

  8. Na5RbCu4(AsO4)4Cl2: Far-infrared spectroscopy • Low frequency phonon modes • No structural phase transition below 60K T.Rõõm, U. Nagel, D. Hüvonen

  9. Na5RbCu4(AsO4)4Cl2: Polarization dependence • Optical properties are isotropic in the ac-plane Step 15deg T.Rõõm, U. Nagel, D. Hüvonen

  10. Na5RbCu4(AsO4)4Cl2: FIR in magnetic field T. Rõõm, et al.

  11. Na5RbCu4(AsO4)4Cl2: magnetization up to 40T Change of slope around 15T at 0,5K Stern, et al., unpublished

  12. Na5RbCu4(AsO4)4Cl2: magnetization up to 40T No change of slope around 15T at 20K? Stern, et al., unpublished

  13. Na5RbCu4(AsO4)4Cl2: magnetization up to 40T Temperature dependence for B in ac plane Stern, et al., unpublished

  14. Na5RbCu4(AsO4)4Cl2: magnetization and ESR Please ignore the black line - will check its accuracy Raivo Stern, et al., unpublished

  15. 3.23 Å 4.19 Å 3.24 Å a 4.26 Å c Spin-exchange Interactions between Neighboring Cu2+ Cations Spin-exchange coupling constants: superexchange: Ja 6 meV, Jc 3 meV super-superexchange: J’a 6 meV, J’c 5 meV

  16. rarely seen Na6O8 cluster Partial Structure of Salt Lattice

  17. Connectivity at Covalent/Ionic Interface Na6O8 cluster in Na5RbCu4(AsO4)4Cl2 Na -O = 2.31 Å - 2.57 Å Na ···Na = 3.51 Å - 3.56 Å

  18. Environment of Na+ Cations

  19. Resolved Na+ Sites in RT MAS NMR Stern, et al., unpublished

  20. Low-Temp NaMAS NMR 294.5K 203.5K 139.0K 107.4K 106.3K 104.3K 87.4K 86.3K 85.6K 72.4K 40.7K 200 100 0 -100 -200 -300 -400 ppm

  21. A single Rb+ Site in RT MAS NMR Stern, et al., unpublished

  22. Na5RbCu4(AsO4)4Cl2: single crystal 87Rb NMR B0 = 14.1 T || [010] • Direct observation of the transition into the AFM ordered phase • (TN = 14.3 K in B0 = 14.1 T) • (ii) The complicated 87Rb NMR line shape suggests a complicated, incommensurate (IC) ordered phase • (iii) A plane-wave modulated IC spin state? Stern, et al., unpublished

  23. 87Rb Quadrupolar Coupling

  24. 87Rb NMR Linewidth

  25. Tentative Phase Diagram AFM LT1 PM LT2 T 74 110 0 50 100 150 200 250 300 N Temperature [K]

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