Dresden 2020 – wissenschaftliches Programm

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TT: Fachverband Tiefe Temperaturen

TT 5: Frustrated Magnets - General 1 (joint session TT/MA)

TT 5.6: Vortrag

Montag, 16. März 2020, 10:45–11:00, HSZ 304

Effective chainlike physics in frustrated S = 1/2 spin-trimer Heisenberg magnets Na2Cu3Ge4O12 and K2Cu3Ge4O12 — •Oleg Janson1 and Satoshi Nishimoto1,21Leibniz Institute für Festkörper- und Werkstoffforschung (IFW Dresden) — 2Technische Universität Dresden (TU Dresden)

The trimerized S = 1/2 Heisenberg magnet Na2Cu3Ge4O12 exhibits an incommensurate magnetic order below TN = 2 K [1], which is nearly two orders of magnitude smaller than the Weiss temperature θW ≃ 200 K. Its potassium sibling K2Cu3Ge4O12 features similar structural Cu3O8 trimers, but their connectivity is different. Here, despite the sizable antiferromagnetic θW = 49 K, the magnetic susceptibility χ(T) reveals no sign of long-range magnetic ordering down to 2.5 K [2]. For both materials, χ(T) data can not be described within the Heisenberg trimer model. To provide a microscopic insight into the spin models of both materials, we perform microscopic modeling by means of DFT band structure calculations. We find, besides the dominant intertrimer exchange J1, three (two) further antiferromagnetic exchanges that give rise to a quasi-1D frustrated model in Na2Cu3Ge4O12 (K2Cu3Ge4O12). The ground states of the spin Hamiltonians are studied using exact diagonalization and DMRG. We also compute the central charge c and the static structure factor S(q), and discuss the possibility to describe the physics of these highly frustrated materials within an effective Heisenberg chain model.
[1] Y. Yasui et al., J. Appl. Phys. 115, 17E125 (2014).
[2] C. Stoll et al., Inorg. Chem. 57, 14421 (2018).

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