Electron Spin Polarization : a New Tool in Photoemission and Magnetism

A review of the technique of measuring the spin polarization P of photoemitted electrons and of results of measurements from a variety of magnetic materials is presented. Photoelectric magnetization curves are obtained by measuring P as a function of applied magnetic field, while measuring P as a function of photon energy gives a spectrum of spin polarization which locates magnetic states in an energy level scheme. The positive P observed for Ni and Co is in disagreement with the predictions of the band model of ferromagnetisrn. On disordering, magnetic semiconductors exhibit new states in the gap which are found to be singly occupied and to enhance the ferromagnetic coupling of the localized 4f spins. At the single crystal surface of the Heisenberg ferromagnet EuO a paramagnetic sheet was found to exist. This dead layer causes spin exchange scattering for electrons emitted from the ferromagnetic bulk. P is found to increase on doping with trivalent metal ions : excess electrons enhance the molecular field in the paramagnetic surface sheet. 1 . Photoelectrons from magnetic materials exhibit electron spin polarization (ESP). If the spindirection is not severely affected in the process of photoemission, electrons emitted from magnetic materials must show a spin polarization. Conservation of the expectation value of spin direction is usually t o be expected in photoemission, because the enlission processes are fast compared t o the spin relaxation