Correlated proton disorder and frustrated magnetism in hydroxide perovskites

氢氧化物钙钛矿代表了一类丰富的材料，最近被证明具有相关的质子无序，类似于六边形水冰中已知的质子无序。这些化合物中有许多是磁性过渡金属离子。特别令人感兴趣的是所谓的双羟基钙钛矿，其在B位点上具有磁性和非磁性过渡金属离子的岩盐型排列，其实现几何上受抑的fcc磁性亚晶格。面心立方晶格上的阻挫磁性理论是当前研究的一个热门课题，这表明这种磁性模型可能对实现量子无序基态（自旋液体）有很大的希望。然而，这种晶格的实验实现仍然非常有限。氢氧化物钙钛矿的高化学可调性使其成为研究阻挫磁性的良好平台，但迄今为止缺乏对其磁性的实验表征。对于一些含有5d过渡金属离子（例如Ir）的双羟基钙钛矿，甚至晶体结构也有待澄清。因此，在这个项目中，我们打算合成磁性氢氧化物钙钛矿，进行晶体学表征，并通过热力学测量和中子散射研究其磁性。我们的项目最终旨在解决的核心科学问题之一是质子无序与磁挫折的相互作用。我们将使用实验参数，如温度和静水压力来调整质子动力学，甚至可能驱动一些系统的质子有序过渡，这应该让我们直接观察质子动力学对磁关联的影响在挫折自旋系统的第一次。

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.