Abstract
A fully relativistic multiple scattering theory for low-energy electron diffraction (LEED) from ferromagnets has been extended to allow for arbitrary magnetisation orientation and to take account of thermal lattice vibrations. Time-reversal and spatial symmetries were used to derive general results and to reduce the computational labour. Numerical results are presented for the ferromagnetic surfaces Ni(001), Fe(110) and Gd(0001). The exact spin-orbit and exchange-induced scattering asymmetries are found to be excellently approximated by spin-orbit-only and exchange-only asymmetries as well as by experimentally more convenient asymmetries in the cases of Ni and Fe, and more moderately so in the case of Gd. A new type of scattering asymmetry, which is brought about by an interplay between spin-orbit and exchange interaction already for unpolarised primary electrons, is predicted to reach sizeable values (up to about 40% for Gd) and to respond very sensitively to assumed changes in the magnetisation of the top layer. This suggests, firstly, the feasibility of studying surface ferromagnetism by unpolarised LEED and, secondly, an enhanced accuracy and reliability when using polarised electrons.