THE TEMPERATURE AND PRESSURE-DEPENDENCE OF THE FERMI CONTACT FIELD OFPOSITIVE MUONS IN FERROMAGNETIC NI

The spin precession frequency omega mu/pi 2 of positive muons and the transverse mu(+) spin relaxation rate Gamma(2) have been measured on t hree Ni single crystals as a function of temperature and hydrostatic p ressure between 7 and 660 K and up to pressures of 0.6 GPa. It is show n that above 260 K the Fermi contact field acting on the mu(+) magneti c moments is proportional to the saturation magnetization, whereas at lower temperatures it is temperature independent apart from a small an omaly at about 8 K. The volume dependence B-Fermi does not exhibit any structure that might be attributed to the occupation of metastable si tes by the mu(+). The observed relaxation rates are compatible with th e hypothesis that they are caused by internal strains associated with dislocations.