Inhomogeneous magnetism and superconductivity

非均匀磁性和超导性

• 批准号: EP/F016611/1
• 负责人: Mark Blamire
• 金额: $ 38.74万
• 依托单位: University of Cambridge
• 依托单位国家: 英国
• 项目类别: Research Grant
• 财政年份: 2008
• 资助国家: 英国
• 起止时间: 2008 至 无数据
• 项目状态: 已结题
• 来源: https://gtr.ukri.org/projects?ref=EP%2FF016611%2F1
• 关键词: Inhomogeneous; magnetism; superconductivity

The past fifteen years has seen considerable research into the coupling of superconductivity and magnetism. These two effects are both mediated by coupling between electrons, but ferromagnetism leads to the parallel alignment of spins while conventional (so called spin-singlet) superconductivity requires anti-parallel spin alignment. As a result the coupling of superconductivity into ferromagnets is generally much weaker than the coupling into non-magnetic metals (the so-called proximity effect). However, at very short-range (a few nanometres) the coupling between superconductivity and ferromagnetism at the interface between the two materials results in complex behaviour which is distinct from that of either material. Most notably, the pairs of electrons which are responsible for superconductivity have a rapidly oscillating phase in the ferromagnet which can lead to negative rather than positive supercurrents appearing in devices in which a thin ferromagnetic barrier separates two superconductors. Devices based on this effect are currently being developed for quantum computation. More controversially, a few very recent experiments have detected a much longer-ranged proximity effect in which superconductivity can penetrate a ferromagnet over distances of hundreds on nanometres. This effect seems to be confirmation of theoretical predications that if the magnetism is inhomogeneous (i.e. all the spins do not point in a single direction) or the electrons are 100% spin polarised then a so-called spin-triplet state of superconductivity should appear. The aim of our proposed project is to investigate carefully the conditions required for the formation of this spin-triplet state and to understand how to control it so that potential applications can be developed. In particular we will look at classes of ferromagnet which have a spiral rather than linear magnetic order, we will also grow artificial magnetic structures in which such spirals can be changed by applying a magnetic field and we will explore how the presence of magnetic domain walls (which are regions in which the magnetism changes direction in a material) affects the superconducting properties.

过去15年来，对超导性和磁性的耦合进行了大量研究。这两种效应都是通过电子之间的耦合介导的，但是铁磁性导致旋转的平行比对，而常规（所谓的旋转单词）超导性则需要反行自旋比对。结果，超导性进入铁磁体的耦合通常比耦合到非磁金属（所谓的接近效应）要弱得多。然而，在非常短的范围（一些纳米）下，两种材料之间的界面上的超导性和铁磁学之间的耦合会导致复杂的行为，这与两种材料的耦合都不同。最值得注意的是，负责超导性的一对电子对在铁磁铁中具有迅速振荡的阶段，这可能导致在薄铁磁障碍物分离两个超导体的设备中会导致负面而不是正值的超电流。目前正在开发基于此效果的设备进行量子计算。更具争议性的是，一些最近的一些实验检测到了较长的接近效应，其中超导性可以在数百个纳米的距离内穿透铁磁铁。这种效果似乎是理论上的鉴定，即如果磁性不均匀（即所有旋转都不沿单个方向指向），或者电子是100％自旋极化，则应出现所谓的超导性的自旋旋转状态。我们提议的项目的目的是仔细研究这种自旋三个状态所需的条件，并了解如何控制它，以便可以开发潜在的应用。特别是，我们将研究具有螺旋性而不是线性磁性顺序的铁磁体类别，我们还将种植人工磁性结构，可以通过应用磁场来改变此类螺旋，我们将探索磁性域壁的存在（材料中的磁性方向变化的区域）如何影响超支属性。

项目成果

Evidence for spin mixing in holmium thin film and crystal samples

• DOI: 10.1103/physrevb.83.144518
• 发表时间: 2011-04
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: I. T. Usman;K. Yates;J. Moore;K. Morrison;V. Pecharsky;K. Gschneidner;T. Verhagen;J. Aarts;V. Zverev;J. Robinson;J. Witt;M. Blamire;L. Cohen

Field modulation of the critical current in magnetic Josephson junctions

• DOI: 10.1088/0953-2048/26/5/055017
• 发表时间: 2013-05-01
• 期刊: SUPERCONDUCTOR SCIENCE & TECHNOLOGY
• 影响因子: 3.6
• 作者: Blamire, M. G.;Smiet, C. B.;Robinson, J. W. A.
• 通讯作者: Robinson, J. W. A.

Critical current of a Josephson junction containing a conical magnet

包含锥形磁体的约瑟夫森结的临界电流

• DOI: 10.1103/physrevb.79.224505
• 发表时间: 2009
• 期刊: Physical Review B
• 影响因子: 3.7
• 作者: Halász G