Evaluating the spin model of 5d transition-metal–based anisotropic triangular-lattice antiferromagnets
Low-dimensional spin systems, in which quantum effects are pronounced, provide fertile playground for unusual ground states and magnetic excitations. A prototypical model is the S = 1/2 anisotropic triangular-lattice magnet characterized by antiferromagnetic nearest-neighbor exchanges J and J' along and between chains, respectively. This system interpolates between a one-dimensional spin chain (J'/J = 0) the regular triangular-lattice antiferromagnet (J'/J = 1), and its ground state remains theoretically controvertial. Experimentally, inorganic realizations of the anisotropic triangular lattice have thus far been limited to Cs2CuX4 (X = Cl, Br), making the search for second-generation model compounds an important objective.
As a new family of model compounds, our collaborators Prof. D. Hirai recently developed the mixed-anion series A3ReO5X2 containing the 5d transition metal renium. In this system, the A site can be substituted with Ca, Sr, Ba, or Pb, and the halogen site X with Cl or Br, allowing a total of seven compounds to be synthesized. Using high-field magnetization measurements combined with finite-temperature Lanczos calculations, we showed that the exchange-anisotropy ratio J'/J spans a broad range of 0.25–0.45 across the series [A, B]. In the Ca-based members, the absence of inversion symmetry in the crystal structure gives rise to a Dzyaloshinskii–Moriya interaction, whereas in Pb3ReO5Cl2, relatively strong interlayer exchange, mediated as a perturbation by electron hopping through Pb 6p orbitals, leads to a magnetic phase transition at low temperatures [B]. By contrast, the Sr- and Ba-based compounds do not exhibit magnetic long-range order down to the lowest temperatures. μSR and inelastic neutron scattering reveal dynamic spin fluctuations and magnetic excitations indicative of a Tomonaga–Luttinger liquid [B]. These findings demonstrate that the spin Hamiltonian of A3ReO5X2 can be tuned flexibly by chemical substitution, and they provide significant new insight into the ground states of anisotropic triangular-lattice antiferromagnets.
[B] M. Gen et al., Nat. Commun. in press. [arXiv:2311.06040]
As a new family of model compounds, our collaborators Prof. D. Hirai recently developed the mixed-anion series A3ReO5X2 containing the 5d transition metal renium. In this system, the A site can be substituted with Ca, Sr, Ba, or Pb, and the halogen site X with Cl or Br, allowing a total of seven compounds to be synthesized. Using high-field magnetization measurements combined with finite-temperature Lanczos calculations, we showed that the exchange-anisotropy ratio J'/J spans a broad range of 0.25–0.45 across the series [A, B]. In the Ca-based members, the absence of inversion symmetry in the crystal structure gives rise to a Dzyaloshinskii–Moriya interaction, whereas in Pb3ReO5Cl2, relatively strong interlayer exchange, mediated as a perturbation by electron hopping through Pb 6p orbitals, leads to a magnetic phase transition at low temperatures [B]. By contrast, the Sr- and Ba-based compounds do not exhibit magnetic long-range order down to the lowest temperatures. μSR and inelastic neutron scattering reveal dynamic spin fluctuations and magnetic excitations indicative of a Tomonaga–Luttinger liquid [B]. These findings demonstrate that the spin Hamiltonian of A3ReO5X2 can be tuned flexibly by chemical substitution, and they provide significant new insight into the ground states of anisotropic triangular-lattice antiferromagnets.
References
[A] S. A. Zvyagin, M. Gen et al., Nat. Commun. 13, 6310 (2022). (Original paper [17])[B] M. Gen et al., Nat. Commun. in press. [arXiv:2311.06040]
