Thin film, near-surface and multi-layer investigations by low-energy mu+SR

At the Paul Scherrer Institute (PSI, Villigen, Switzerland) the beam of low-energy positive polarised muons (LE-mu(+)) with tunable energy between 0.5 and 30 keV allows the extension of the muon-spin-rotation technique (mu SR) to studies on thin films and multi-layers (LE-mu+SR). The range of these muons in solids covers the near-surface region up to implantation depths or about 300 nm. As a sensitive local magnetic probe with a complementary observation time window to other techniques LE-mu+SR offers the unique possibility to gain new insights in these nano-scale objects. After outlining the current status of the LE-mu(+) beam line we demonstrate the potential of this new technique by presenting the results of recent experiments: i) the direct observation of non-local effects in a superconducting Pb film, ii) the oxygen isotope effect on the in-plane penetration depth in optimally doped YBa2Cu3O7-delta, and iii) the first observation of the conduction electron spin polarisation in the Ag spacer of a Fe/Ag/Fe tri-layer.