Sergei Zvyagin, HLD Dresden.

Spin-1/2 triangular-lattice Heisenberg antiferromagnets represent one of the most important classes of frustrated quantum magnets, demonstrating a complex interplay between geometrical frustration, quantum fluctuations, and magnetic order. In spite of their simple magnetic structures (Figure, inset), they possess highly unusual magnetic properties and a very rich – and not fully understood – phase diagram. One major obstacle in this area of research is the lack of materials with appropriate, ideally tuned, magnetic parameters. Using Cs2CuCl4 as a model system, we demonstrate an alternative approach, where, instead of the chemical composition, the spin Hamiltonian is altered by hydrostatic pressure. The approach combines high-pressure high-field electron spin resonance (ESR), performed at the Tohoku University in Sendai, Japan, and magnetization measurements, done at the National High Magnetic Laboratory in Tallahassee, USA. The results allowed us not only to quasi-continuously tune the exchange parameters, but also to accurately monitor them by measuring the pressure-dependent shift of the ESR lines (Figure). The application of a pressure of up to about 2 GPa increases the exchange-coupling parameters in this compound by up to 70%, triggering, at the same time, a cascade of new low-temperature field-induced phase transitions, absent at zero pressure.

Figure: Pressure dependence of ESR in Cs2CuCl4 at 1.9 K. a) Frequency-field diagram of magnetic excitations at different pressures, i.e., acoustic (mode A) and optical (mode B) magnon. The inset shows a schematic picture of magnetic sites and exchange couplings in a triangular layer of Cs2CuCl4. b) ESR spectra of the optical magnons taken at a frequency of 330 GHz at different pressures (the spectra are offset for clarity).

Pressure-tuning the quantum spin Hamiltonian of the triangular lattice antiferromagnet Cs2CuCl4, S. A. Zvyagin, D. Graf, T. Sakurai, S. Kimura, H. Nojiri, J. Wosnitza, H. Ohta, T. Ono, and H. Tanaka, Nat. Commun. 10, 1064 (2019).

https://www.nature.com/articles/s41467-019-09071-7

Contact: S.Zvyagin@hzdr.de