Thermodynamics of Spin-Orbital Coupled Magnets: The Case of Dimers and Timers

Recently, there has been great interest in 4d and 5d magnetic insulators with strong spin-orbit coupling (SOC) - which have shown the potential to realise low-energy spin Hamiltonians featuring a variety of complex anisotropic couplings of fundamental interest. In this contribution, we focus on the theoretical description of recently reported spin-liquid candidate materials based on mixed valence M₂O₉ dimers [1] and M₃O₁₂ trimers [2,3]. The challenge of modelling these materials lies in their complex local electronic structures, which should manifest in e.g. complex spin-orbital ground states, instabilities towards charge order, and strong structural sensitivity of the magnetic response. We focus, in particular, on experimental signatures and consequences of various possible ground states as a function of SOC strength and electronic filling. Of particular experimental importance is the inapplicability of Curie-Weiss analysis due to the non-commutability of SOC with magnetic fields.

[1] T. Dey, et al., Phys. Rev. B 96, 174411 (2017).
[2] L. T. Nguyen, et al., Phys. Rev. Materials 3, 014412 (2019).
[3] G. Cao, et al., arXiv: 1901.04125 (2019).