Muon spin rotation and relaxation experiments on thin films

The recent development at the Paul Scherrer Institute of a beam of low ener gy muons allows depth dependent muon spin rotation and relaxation investiga tions in thin samples, multilayers and near surface regions (low energy mu SR, LE-mu SR). After a brief overview of the LE-mu SR method, some represen tative experiments performed with this technique will be presented. The fir st direct determination of the field profile just below the surface of a hi gh-temperature superconductor in the Meissner phase illustrates the power a nd sensitivity of low energy muons as near-surface probe and is an example of general application to depth profiling of magnetic fields. The evolution of the flux line lattice distribution across the surface of a YBa2Cu3O7 fi lm in the vortex phase has been investigated by implanting muons on both si des of a normal-superconducting boundary. A determination of the relaxation time and energy barrier to thermal activation in iron nanoclusters, embedd ed in a silver thin film matrix (500 nm), demonstrates the use of slow muon s to measure the properties of samples that cannot be made thick enough for the use of conventional mu SR. Other experiments investigated the magnetic properties of thin Cr(001) layers at thicknesses above and below the colla pse of the spin density wave.