Study of magnetic and electronic phase diagrams of novel Kondo Insulators, Heavy Fermions and complex oxides

新型近藤绝缘体、重费米子和复合氧化物的磁相图和电子相图研究

• 批准号: 278191572
• 负责人: Professor Dr. Jochen Litterst
• 金额: --
• 依托单位: Theoretical Physics Department (aufgelöst)
• 依托单位国家: 德国
• 项目类别: Research Grants
• 财政年份: 2015
• 资助国家: 德国
• 起止时间: 2014-12-31 至 2022-12-31
• 项目状态: 已结题
• 来源: https://gepris.dfg.de/gepris/projekt/278191572?language=en
• 关键词: Study; magnetic; electronic; phase; diagrams

Transition metal oxides A2B’B‘‘O6 having double perovskite structure often possess extraordinary magnetic and electronic properties. The systems La2-xCaxCoIrO6 and La2-xAxCoMnO6 (A=Ca,Sr or Ba) show composition dependent electronic valency states of Co, Mn and Ir causing complex magnetic and electronic phase diagrams. A special peculiarity is a strong so-called spontaneous Exchange Bias behavior. Reason for the strong asymmetry in magnetic hysteresis curves is suspected to be the co-existence of ferro- and antiferromagnetic as well as spin-glassy volumes. Our first investigations of the magnetic properties of these oxides using muon spin rotation (µSR) as local probe at atomic level have revealed that magnetic phase diagrams are more complex than anticipated from macroscopic magnetization measurements. Especially the role of the found electronic spin dynamics still present even at low temperatures and of the spin-glassy volume fractions needs to be clarified. We plan to investigate the magnetic phase diagrams using µSR. The electronic properties will be studied by XPS, XANES and XMCD (cooperation with Brazilian groups). The objective is an improved understanding of the Exchange Bias effects in these materials with the aim of designing new materials with improved properties. The synthesis of the materials to be studied will also be done by the Brazilian groups.In a second part of the project there are studied double perovskites with composition Sr2CuTe1-xWxO6 (x between 0 and 1). These materials possess a strong quasi 2-dimensional magnetic coupling between CuII with Spin ½. For x=0 and 1 µSR an neutron scattering find long-range antiferromagnetic order that can be theoretically well described by magnetic coupling to next and next-nearest Cu. For the solid solutions with x around 0.5 one expects suppression of magnetic order due to frustration of magnetic couplings and disorder. Our first µSR measurements on this systems have confirmed this (no magnetic order observed down to at least 0.25 K) and one may suspect that for mixtures around x=0.5 a quantum spin liquid is appears as ground state. We plan to follow the development of spin dynamics down to lowest temperatures (below 100 mK), to investigate the magnetic phase diagrams for the various compositions x and to compare our results with theoretical model calculations for the magnetic coupling.

具有双钙钛矿结构的过渡金属氧化物A2B‘B’O6往往具有优异的磁学和电学性质。La_(2-x)CaxCoIrO_6和La_(2-x)Co_xCoMnO_6(A=Ca、Sr或Ba)体系显示Co、Mn和Ir的电子价态与组成有关，产生了复杂的磁相图和电子相图。一个特殊的特点是强烈的所谓的自发交换偏向行为。磁滞回线高度不对称的原因可能是铁磁和反铁磁以及自旋玻璃化体积的共存。我们首次使用µSR作为原子水平上的局域探针对这些氧化物的磁性进行了研究，发现磁性相图比宏观磁化测量所预期的要复杂得多。特别是，发现的电子自旋动力学的作用即使在低温下仍然存在，自旋玻璃化体积分数的作用需要澄清。我们计划使用µSR来研究磁相图。电子性质将通过XPS、XANES和XMCD(与巴西集团合作)进行研究。目的是为了更好地理解这些材料中的交换偏置效应，目的是设计具有更好性能的新材料。在该项目的第二部分中，研究了组成为Sr2CuTe1-xWxO6(x介于0和1之间)的双钙钛矿。这些材料在CuII和自旋1/2之间具有很强的准2维磁耦合。对于x=0和1µSR，中子散射发现了长程反铁磁序，理论上可以很好地用与次近邻的铜的磁耦合来描述。对于x约为0.5的固溶体，由于磁耦合和无序的受挫，预计磁有序被抑制。我们在这个系统上的第一次µSR测量证实了这一点(没有观察到至少0.25K的磁序)，人们可能会怀疑，对于x=0.5左右的混合物，量子自旋液体似乎是基态。我们计划跟踪自旋动力学的发展，直到最低温度(低于100MK)，研究不同成分x的磁相图，并将我们的结果与磁耦合的理论模型计算进行比较。