Intrinsic Pinning in Magnetic Iron-Based Superconductors; a Route to High Critical Current Conductors at High Magnetic Fields

磁性铁基超导体的本征钉扎；

• 批准号: EP/X015033/1
• 负责人: Simon Bending
• 金额: $ 58.16万
• 依托单位: University of Bath
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2023
• 资助国家: 英国
• 起止时间: 2023 至 无数据
• 项目状态: 未结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FX015033%2F1
• 关键词: Intrinsic; Pinning; Magnetic; Iron; Based

The discovery of superconductivity by Kamerlingh Onnes in 1911 was one of the most remarkable discoveries of the 20th century. A superconductor is a material that can carry large electrical currents without any resistance, that is without losing any energy. Although superconductors offered clear benefits for the transmission of electrical power, many problems needed to be solved before they could find mainstream applications. The first discovered superconductors had to be cooled to extremely low temperatures, close to absolute zero on the Kelvin scale, requiring the development of suitable cryogenic cooling systems which themselves had significant energy losses. Since the discovery of copper oxide-based superconductors in 1986 and iron-based superconductors in 2006 with much higher operation temperatures, this problem has been largely solved. However, we now know that only certain types of superconducting materials, so-called 'type II' ones, are capable of operation at the very high magnetic fields needed for medical magnetic resonance imaging or magnetic confinement in fusion reactors. However, these 'type II' materials are only able to achieve this by allowing tiny tubes of magnetic field called vortices to enter them which start to generate heat (and lose energy) if they are driven into motion by large flowing supercurrents. Fortunately nature has found a solution to this problem, and vortices can become trapped at defects present in the material preventing them from moving and losing energy. Developing high current superconducting wires therefore requires introducing as many defects into the material as possible without significantly degrading other useful superconducting properties. Even then the current carrying capacity of superconductors at very high magnetic fields (when they become flooded with many vortices) can still be too low for intended applications. In this project we will investigate new types of iron-based superconductors that have recently been discovered in which magnetism and superconductivity coexist. This behaviour is very unusual as magnetism and superconductivity are normally antagonistic phenomena; they involve opposite arrangements of the quantum spins of electrons. Each electron can be visualised as having a tiny compass 'needle' (the spin) attached to it; in ferromagnets all the 'needles' point in the same direction, while in conventional superconductors the electrons form pairs in which the 'needles' point in opposite directions. Remarkably, in these new iron-based materials the presence of ferromagnetism does not destroy superconductivity, and a patchwork of regions called domains where the magnetic 'needles' point in different directions coexists with the superconducting state. These magnetic domains and the boundaries between them represent a new type of defect that can strongly trap vortices, leading to enhanced current carrying capacities, even in very high magnetic fields.In this project we will bring together a team of experts with a diverse range of skills that can grow, pattern, measure and undertake theoretical studies on magnetic iron-based superconductors. We will carefully investigate how the patchwork of magnetic domains present can trap superconducting vortices and control their dynamic properties and will develop advanced theoretical models to understand our results. Once the conditions have been established for achieving the highest current densities at high magnetic fields we will apply them to iron-based superconducting thin films grown by our partner in Karlsruhe (Germany) with the ultimate goal of realising high performance commercial wires that can be produced by very low-cost methods. Although the main motivation for this project is to develop new materials that meet the requirements for key applications, we will also generate a lot of new scientific knowledge that will be of great value to the wider research community working on superconducting materials.

Kamerlingh Onnes 于 1911 年发现的超导性是 20 世纪最引人注目的发现之一。超导体是一种可以承载大电流而没有任何电阻，即不损失任何能量的材料。尽管超导体为电力传输提供了明显的好处，但在其获得主流应用之前还需要解决许多问题。第一个发现的超导体必须冷却到极低的温度，接近开尔文温标的绝对零，需要开发合适的低温冷却系统，而该系统本身会产生巨大的能量损失。自从1986年发现氧化铜基超导体和2006年工作温度更高的铁基超导体以来，这个问题已在很大程度上得到解决。然而，我们现在知道，只有某些类型的超导材料，即所谓的“II 型”材料，能够在医学磁共振成像或聚变反应堆磁约束所需的极高磁场下工作。然而，这些“II 型”材料只能通过允许称为涡流的微小磁场管进入它们来实现这一点，如果它们被大流动的超电流驱动运动，涡流就会开始产生热量（并损失能量）。幸运的是，大自然已经找到了解决这个问题的方法，涡流可能会被材料中存在的缺陷所困，从而阻止它们移动和损失能量。因此，开发高电流超导线材需要在材料中引入尽可能多的缺陷，而不会显着降低其他有用的超导性能。即使这样，超导体在极高磁场下（当它们被许多涡流淹没时）的载流能力对于预期应用来说仍然太低。在这个项目中，我们将研究最近发现的新型铁基超导体，其中磁性和超导性共存。这种行为非常不寻常，因为磁性和超导通常是对立的现象。它们涉及电子量子自旋的相反排列。每个电子都可以被想象为附有一个微小的罗盘“针”（自旋）；在铁磁体中，所有“针”都指向同一方向，而在传统超导体中，电子形成对，其中“针”指向相反的方向。值得注意的是，在这些新型铁基材料中，铁磁性的存在不会破坏超导性，并且磁“针”指向不同方向的称为磁域的区域拼凑而成，与超导状态共存。这些磁域及其之间的边界代表了一种新型缺陷，可以强烈捕获涡流，从而增强载流能力，即使在非常高的磁场中也是如此。在这个项目中，我们将汇集具有不同领域的专家团队。可以培养、设计、测量和进行磁性铁基超导体理论研究的技能。我们将仔细研究拼凑而成的磁域如何捕获超导涡旋并控制其动态特性，并将开发先进的理论模型来理解我们的结果。一旦在高磁场下实现最高电流密度的条件确立，我们将把它们应用于我们在卡尔斯鲁厄（德国）的合作伙伴生长的铁基超导薄膜，最终目标是实现可生产的高性能商业电线通过非常低成本的方法。尽管该项目的主要动机是开发满足关键应用要求的新材料，但我们也将产生大量新的科学知识，这些知识对于更广泛的超导材料研究界具有重要价值。