Browsing by Author "Ponomaryov, A.N."

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    Dimensional reduction and incommensurate dynamic correlations in the S=1/2 triangular-lattice antiferromagnet Ca3ReO5Cl2
    ([London] : Nature Publishing Group UK, 2022) Zvyagin, S.A.; Ponomaryov, A.N.; Wosnitza, J.; Hirai, D.; Hiroi, Z.; Gen, M.; Kohama, Y.; Matsuo, A.; Matsuda, Y.H.; Kindo, K.
    The observation of spinon excitations in the S=1/2 triangular antiferromagnet Ca3ReO5Cl2 reveals a quasi-one-dimensional (1D) nature of magnetic correlations, in spite of the nominally 2D magnetic structure. This phenomenon is known as frustration-induced dimensional reduction. Here, we present high-field electron spin resonance spectroscopy and magnetization studies of Ca3ReO5Cl2, allowing us not only to refine spin-Hamiltonian parameters, but also to investigate peculiarities of its low-energy spin dynamics. We argue that the presence of the uniform Dzyaloshinskii-Moriya interaction (DMI) shifts the spinon continuum in momentum space and, as a result, opens a zero-field gap at the Γ point. We observed this gap directly. The shift is found to be consistent with the structural modulation in the ordered state, suggesting this material as a perfect model triangular-lattice system, where a pure DMI-spiral ground state can be realized.
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    Extremely well isolated two-dimensional spin-1/2 antiferromagnetic Heisenberg layers with a small exchange coupling in the molecular-based magnet CuPOF
    (Woodbury, NY : Inst., 2020) Opherden, D.; Nizar, N.; Richardson, K.; Monroe, J.C.; Turnbull, M.M.; Polson, M.; Vela, S.; Blackmore, W.J.A.; Goddard, P.A.; Singleton, J.; Choi, E.S.; Xia, F.; Williams, R.C.; Lancaster, T.; Pratt, F.L.; Blundell, S.J.; Skourski, Y.; Uhlarz, M.; Ponomaryov, A.N.; Zvyagin, S.A.; Wosnitza, J.; Baenitz, M.; Heinmaa, I.; Stern, R.; Kühne, H.; Landee, C.P.
    We report on a comprehensive characterization of the newly synthesized Cu2+-based molecular magnet [Cu(pz)2(2-HOpy)2](PF6)2 (CuPOF), where pz=C4H4N2 and 2-HOpy=C5H4NHO. From a comparison of theoretical modeling to results of bulk magnetometry, specific heat, μ+SR, ESR, and NMR spectroscopy, this material is determined as an excellent realization of the two dimensional square-lattice S=12 antiferromagnetic Heisenberg model with a moderate intraplane nearest-neighbor exchange coupling of J/kB=6.80(5) K, and an extremely small interlayer interaction of about 1 mK. At zero field, the bulk magnetometry reveals a temperature-driven crossover of spin correlations from isotropic to XY type, caused by the presence of a weak intrinsic easy-plane anisotropy. A transition to long-range order, driven by the low-temperature XY anisotropy under the influence of the interlayer coupling, occurs at TN=1.38(2) K, as revealed by μ+SR. In applied magnetic fields, our H1-NMR data reveal a strong increase of the magnetic anisotropy, manifested by a pronounced enhancement of the transition temperature to commensurate long-range order at TN=2.8 K and 7 T. © 2020 authors.