Electron-lifetime anisotropy in magnesium

De Haas--van Alphen measurements have been performed to study electron lifetimes in ultrapure magnesium and in very dilute magnesium alloys. For selected orbits the observed Dingle temperatures (T/sub D/) were found to be independent of magnetic field direction for fields in the basal plane, whereas in the (1010) plane a strong anisotropy was observed. In pure magnesium T/sub D/ decreased by a factor of 5 as the field was rotated from the <1120 > axis towards <0001>, reaching a minimum value of less than 0.08 K, which corresponds to an electron lifetime of at least 1.5 x 10-11 sec for these orbits. The lifetime anisotropy is attributed to dislocation scattering in these crystals for which the dislocation density was characterized experimentally and found to be in the range of 103--105 cm-2. The results are compared with previous de Haas--van Alphen studies of dislocations, as well as previous lifetime measurements obtained by the electron-interference technique. An analysis in terms of the dephasing theory due to Watts is presented, and it is suggested that the presence of dislocation multipole arrays is important