Correlated proton disorder and frustrated magnetism in hydroxide perovskites

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Hydroxide perovskites represent a rich class of materials that were recently demonstrated to host correlated proton disorder, similar to that known in hexagonal water ice. Many of these compounds host magnetic transition-metal ions. Of particular interest are so-called double hydroxyperovskites with a rock-salt–type arrangement of magnetic and nonmagnetic transition-metal ions on the B site, which realize a geometrically frustrated fcc magnetic sublattice. The theory of frustrated magnetism on the fcc lattice is a subject of intense current research, indicating that this magnetic model may hold great promises for the realization of quantum-disordered ground states known as spin liquids. However, experimental realizations of such lattices remain very limited. The high chemical tunability of hydroxide perovskites makes them an excellent platform for studying frustrated magnetism, yet the experimental characterization of their magnetic properties are lacking until now. For some double hydroxyperovskites containing 5d transition-metal ions (such as Ir, e.g.), even the crystal structure still awaits to be clarified. Therefore, in this project we intend to synthesize magnetic hydroxide perovskites, perform their crystallographic characterization, and study their magnetic properties by thermodynamic measurements and neutron scattering. One of the central scientific questions that our project ultimately aims to address is the interplay of proton disorder with magnetic frustration. We will use experimental parameters such as temperature and hydrostatic pressure to tune the proton dynamics, perhaps even driving some of the systems to a proton-ordering transition, which should let us directly observe the influence of proton dynamics on magnetic correlations in a frustrated spin system for the first time.