Magnetic field induced phases in one-dimensional (1D) antiferromagnetic quantum magnets

低维量子磁体表现出许多新的现象，特别是奇异(场致)相。特别是对于磁耦合路径的几何受挫情况，已经观察到了许多不同的新相，但到目前为止还没有全面的理论理解。因此，对于这一主题，从实验方面来说，有必要对这些相进行详细的描述，以便为理论建模定义基准。在这一后续项目中，我们计划研究受挫低维量子磁体中的这种场诱导相，因为这些相以一种独特的方式代表了(几乎完全)可计算的模型系统。该项目包括研究(I)受挫的海森堡链亚麻酸铅矿中的场诱导相，以及(Ii)Kagome体系Haydeeite的(压力相关)基态性质。在之前的项目中，我们首次用微观宏观技术广泛地表征了Liarit PbCuSO_4(OH)_2体系。作为我们研究的结果，我们可以将该材料建模为具有铁磁近邻和反铁磁次近邻耦合的受挫自旋链。此外，我们首次确定了一系列新的相，这再次带来了一系列新的科学主题。我们现在希望详细讨论这些主题。此外，在第二个子项目中，我们计划详细研究受挫的Kagome晶格陶粒Cu3 Mg(OH)6Cl2的性质。从最近的文献中发现，理论预测与实验观察之间存在显著的差异。此外，实验观察本身既不是完全确定的，也不是没有矛盾的。根据我们在确定这类受挫磁体中复合态的经验，我们希望对海泡石的性质进行相应的研究。为了对基本现象有一个全面而连贯的概念，在这两种情况下，我们计划将热力学研究与微观核磁共振研究和(In)弹性中子散射结合起来，这是外部参数如压力或磁场的函数。

Low-dimensional quantum magnets exhibit a multitude of novel phenomena, notably such as exotic (field-induced) phases. Especially for the case of geometrical frustration of the magnetic coupling paths a number of different and new phases have been observed, while so far there is no comprehensive theoretical understanding. Therefore, regarding this topic, from the experimental side there is need for a detailed description of such phases, in order to define benchmarks for theoretical modellings.Within this follow-up projects, we plan to investigate such field-induced phases in frustrated low-dimensional quantum magnets, as these represent in a unique manner model systems that are (almost exactly) computable. The project covers studies on (i) the field-induced phases in the frustrated Heisenberg chain linarite, as well as on (II) the (pressure dependent) ground state properties of the Kagome system haydeeite.Within the preceeding project, for the first time we have extensively characterized the system Linarit PbCuSO_4(OH)_2 using micro- as macroscopic techniques. As result of our investigations we could model the material as frustrated spin chain, with a ferromagnetic nearest-neighbor and an antiferromagnetic next-nearest-neighbor coupling. Further, for the first we have identified a series of novel phases, which again brought a series of new scientific topics. These topics we wish to address now in detail. Furthermore, in a second subproject we plan to study in detail the properties of the frustrated Kagome lattice haydeeite Cu_3Mg(OH)_6Cl_2. From recent publications it was found that there are significant discrepancies between theoretical prediction and experimental observation. Moreover, the experimental observations itself are neither fully established nor free of contradictions. With our experience in determining complex states in such frustrated magnets we wish to carry a corresponding study of the properties of haydeeite.To obtain a comprehensive and coherent idea of the basic phenomena, in both cases we plan to combine thermodynamic studies with microscopic NMR investigations and (in)elastic neutron scattering, this as function of external parametters such as pressure or magnetic field.