A POLARISED POSITRON BEAM FOR PROBING MAGNETIC STRUCTURES

这项拟议的研究是一项为期12个月的试点项目，旨在开发和测试一束单能自旋极化正电子束，然后将其用作具有科学和技术意义的材料中原子和纳米尺度的磁性结构的探测器。人们发现，使用放射性同位素产生的低能正电子束具有高度极化，这一发现得到了广泛报道，但除了一两个早期的演示实验外，从未被利用过。磁性材料(如用于技术应用的磁性半导体、磁性纳米粒子)物理学中的新问题表明，非破坏性的、深度敏感的极化正电子束应该可以有效地作为这些系统中自旋极化电子的探测器。目前一个重要的例子是化合物半导体中与磁性锰相关的团簇的形成和迁移问题，其中偏振正电子能谱应该是一个很好的探针。为了对测试样品进行中试实验，巴斯大学的标准磁传输束必须进行改装，主要是在源/慢化剂阶段。这项提案要求提供资金，以便能够购买合适的来源胶囊，安装和启用对现有仪器进行必要的更改，并进行试验性测量，以测试其有效性。成功将使巴斯集团走在这一领域世界活动的前列。

The proposed research is a 12-month pilot project to develop and test a beam of mono-energetic spin-polarised positrons which can then be used as a probe of magnetic structures on the atomic and nanoscale in materials of scientific and technological interest.The discovery that low-energy positron beams created using radioactive isotopes are highly polarised has been widely reported but, apart from one or two early demonstration experiments, has never been exploited. New questions in the physics of magnetic materials (eg magnetic semiconductors for technological applications, magnetic nanoparticles) suggest that a non-destructive, depth-sensitive polarised positron beam should be effective as a probe of spin-polarised electrons in these systems. An important current example is the issue of magnetic manganese-related cluster formation and migration in compound semiconductors, of which polarised positron spectroscopy should be an excellent probe. In order to perform pilot experiments on test samples the standard magnetic-transport beam at the University of Bath has to be modified, principally at the source/moderator stage. This proposal asks for funds to enable the purchase of a suitable source capsule and to install and commission the necessary changes to the existing apparatus, and to perform pilot measurements to test its effectiveness. Success will put the Bath group at the forefront of world activity in this area.