Spin-Polarized Electrons and Magnetism 2000

Abstract

The spin polarization P of the electron states of a ferromagnet is obtained from photoemission experiments provided one corrects for the spinfiltering in the transport of the photoexcited electrons to the surface. It turns out that there exist two types of ferromagnetic metal: one with positive P at the Fermi energy E _f (Fe, Gd, La_0.7Sr_0.3MnO₃ … ) and the other with negative P(Ef) (Ni, Co, Fe₃O₄ …) This together with progress in understanding the role of the metal-oxide interface in determining the spin polarization of the current through magnetic tunnel junctions makes possible the injection of polarized electron currents of either sign from ferromagnetic emitters into quantum wells, insulators, or other ferromagnetic metals leading to a wealth of new insight as well as applications such as realized in GMR-(Giant magnetoresistance) and TMR-(Tunneling magnetic resistance) devices. Generally, in such spin electronics, the electric currents are manipulated through the spin state of the electrons. Basic to the understanding of spin electronics as well as electron emission from solids is the understanding of the spin attenuation in transport of the electrons. We have performed two different experiments to elucidate the underlying spin dependent electron-electron scattering. In the first experiment, the electrons are excited with a femtosecond laser pulse and their spin dependent relaxation is observed via a subsequent laser pulse inducing photoemission. In the second experiment, spin-polarized electrons from a GaAs-type of electron source are injected into a ferromagnetic film and their absorption and spin rotation is observed.