CM Seminar: New Realisations of Frustrated Spin Systems

Dr Lucy Clark, University of Liverpool.

A spin liquid is a unique magnetic state of matter. It is a strongly correlated state but one that can evade conventional long-range magnetic order, even at very low temperatures. Our ability to stabilise spin liquid ground states in magnetic materials is critical to explore and understand their exotic emergent phenomena experimentally. An essential mechanism through which we can suppress long-range magnetic order is by inducing a competition of the magnetic exchange interactions within a material.

Thus, frustrated spin systems, such as geometrically frustrated magnets, are an important class of materials in which to seek and explore spin liquid states. Here, I will give an overview of our recent work in this field. In particular, I will focus on some of the unusual chemical methods we have developed to realise more, and different, frustrated spin systems and our use of a variety of neutron scattering and muon spectroscopy techniques to unravel their nature. I will begin with a discussion of the hexagonal antiferromagnetic, TbInO3, which contains a two-dimensional geometrically frustrated magnetic sublattice of Tb3+ ions.

I will show that, despite significant antiferromagnetic exchange interactions between the Tb3+ ion moments in TbInO3, the system fails to order above 100 mK. We believe that this spin liquid-like behaviour stems from the interplay between crystal field effects and strong spin-orbit coupling and propose a model for the crystal field spectrum of TbInO3 based on our time-of-flight inelastic neutron scattering data [1]. I will then go on to consider magnetic frustration in three-dimensions. In particular, I will briefly discuss our study of the unconventional spin-glass state in Lu2Mo2O7 [2] and go on to show how we can tune the nature of the magnetic ground state in this family of materials by controlling the oxidation state of Mo ions by thermal ammonolysis.

I will show that our neutron scattering studies of Mo5+-based S = ½ Lu2Mo2O5N2 provide evidence for a gapless spin liquid state [3] driven by enhanced quantum fluctuations in comparison to the parent oxide [4]. Finally, I will touch on our development of novel ionothermal synthesis methods that led to the discovery of the first realisations of V4+-based S = ½ kagome antiferromagnets [5] and our efforts to understand these fascinating new materials [6, 7].

References

[1] L. Clark et al. in preparation (2018).
[2] L. Clark et al. Journal of Solid State Chemistry 203, 199 (2013).
[3] L. Clark et al. Physical Review Letters 113, 117201 (2014).
[4] Y. Iqbal et al. Physical Review Materials 1, 071201(R) (2017).
[5] L. Clark et al. Angewandte Chemie International Edition 54, 15457 (2015).
[6] L. Clark et al. Physical Review Letters 110, 207208 (2013).
[7] J. –C. Orain et al. Physical Review Letters 118, 237203 (2017).