Magnetic and transport properties of ternary iron chalcogenides with reduced dimensionality

本研究计划的重点是一维（1D）线性链状三元铁硫属化物AFeX 2（A = K，Rb，Cs，Tl; X = S，Se）和二维（2D）平面三元铁硫属化物A（1-x）Fe（2−y）X2（A = K，Rb; X = S，Se）的研究。前者在高温下发生反铁磁相变，后者是化学计量比接近2：4：5的反铁磁有序共存的超导体，超导转变温度高于30 K。该项目假设整个研究周期：（i）高质量单晶的合成，（ii）通过广泛的互补实验方法对其物理性质进行详细研究，（iii）对收集的数据进行扩展的常规分析，揭示与所研究材料的降维有关的人工制品，以及（iv）基于能带结构、电子态密度、自旋和电荷分布、电场梯度、声子色散和元素特定声子态密度的现代从头计算，发展自洽统一方法。从热容量，磁矩，红外吸收，电子自旋共振和穆斯堡尔谱测量的实验数据集将在一个一致的方式进行检查的基础上从头算研究的结果。这种扩展的分析将为建立自旋链模型提供坚实的基础，用于解释磁化率随温度升高而异常准线性增加的现象，这种现象在许多线性链铁硫属化物中观察到，在Néel温度以上的很宽的温度范围内。自旋链化合物磁化率的量子统计模型将在我们的测量数据库上开发和验证。FeX 4四面体的共同构建块激发了一维反铁磁自旋链和二维层状超导体的比较研究，重点是磁性和超导性之间的相关性。DFG和RFBR的项目支持将加强奥格斯堡和喀山团队之间的现有合作，并释放两个团队的协同作用。

The proposed research project is focused on the investigation of one-dimensional (1D) linear-chain ternary iron chalcogenides AFeX2 (A = K, Rb, Cs, Tl; X = S, Se) and two-dimensional (2D) planar ternary iron chalcogenides A(1-x)Fe(2−y)X2 (A = K, Rb; X = S, Se). The former undergo an antiferromagnetic phase transition at elevated temperatures, the latter are superconductors with coexisting antiferromagnetic order at stoichiometries close to 2:4:5 with superconducting transition temperatures above 30 K. The project supposes the whole cycle of studies: (i) synthesis of high-quality single crystals, (ii) detailed investigation of their physical properties by means of a wide range of complementary experimental methods, (iii) extended conventional analysis of the collected data, disclosure of the artifacts related to the reduced dimensionality of the studied materials, and (iv) development of a self-consistent unified approach based on modern ab initio calculations of band structures, electron densities of states, spin- and charge distributions, electric-field gradients, phonon dispersions and element specific phonon density of states. The set of experimental data from heat capacity, magnetic moment, infrared absorption, electron spin resonance and Mössbauer spectroscopy measurements will be examined in a consistent way based on results of the ab initio studies. This extended analysis will provide a solid basis for building of spin-chain models for interpreting the unusual quasi-linear increase of magnetic susceptibility with increasing temperature, observed in many of linear-chain iron chalcogenides in a wide range of temperatures above the Néel temperature. Quantum statistical models of the magnetic susceptibility of spin-chain compounds will be developed and verified on the database of our measurements. The common building blocks of FeX4 tetrahedra motivate the comparative investigation of 1D antiferromagnetic spin chains and 2D layered superconductors with the focus on correlations between magnetism and superconductivity. The project support from DFG and RFBR will strengthen the existing collaboration between Augsburg and Kazan teams and unlock the synergy of the two groups working together.