A POLARISED POSITRON BEAM FOR PROBING MAGNETIC STRUCTURES

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.