High pressure mu SR studies: rare earths and related materials

After a short introduction to mu SR with respect to the study of magnetic p roperties, followed by a brief outline of the principle of the high pressur e-low temperature mu SR spectrometer installed at the Paul Scherrer Institu te, we discuss some measurements on rare earth materials employing this ins trument. They are concerned with: (1) The pressure dependence of the spin t urning process in ferromagnetic Gd. (2) The volume dependence of the intern al magnetic field in the heavy rare earth metals Gd, Dy, and Ho in their or dered magnetic states. (3) The response of the (first order) magnetic trans ition in the frustrated antiferromagnets of type RMn2 (R = Y,Gd) to pressur e. (4) The variation of magnetic parameters with pressure in La2CuO4 (powde r sample), the antiferromagnetic parent compound of the high T-C supercondu ctors of type La2-x(Sr, Ba)(x)CuO4. In conclusion a short outlook on furthe r developments is given.