A POLARISED POSITRON BEAM FOR PROBING MAGNETIC STRUCTURES

这项研究是一项为期十二个月的试验计划，目的是发展和测试一束单能自旋极化正电子，然后用作探测具科技价值的材料在原子和纳米尺度上的磁性结构。利用放射性同位素产生的低能正电子束是高度极化的，这一发现已被广泛报道，但除了一两个早期的示范实验外，从未被利用过。磁性材料物理学中的新问题（例如用于技术应用的磁性半导体，磁性纳米颗粒）表明，非破坏性的，深度敏感的极化正电子束应该是这些系统中自旋极化电子的有效探针。目前一个重要的例子是化合物半导体中与磁性锰相关的簇的形成和迁移问题，其中极化正电子光谱应该是一个很好的探针。为了对测试样品进行试验性实验，必须对巴斯大学的标准磁传输束进行修改，主要是在源/慢化剂阶段。该提案要求提供资金，以便能够购买合适的源盒，安装和调试现有设备的必要改动，并进行试点测量以测试其有效性。成功将使巴斯集团在这一领域处于世界活动的前列。

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.