As electrons are injected at various energies into ferromagnetic material with their spin polarization vector perpendicular to the axis of the magnetization, we observe precessional motion of the spin polarization on the femtosecond time scale. Because of angular momentum conservation, the magnetization vector must precess as well. We show that spin injection will generate the precessional magnetization reversal in nanosized ferromagnetic bits. At reasonable injected current densities this occurs on the picosecond time scale.
It is shown that the spin asymmetry of the elastic transmission of electrons through ferromagnetic films can approach unity. The polycrystalline Co films are a few nanometers thick and saturated with the magnetization M in the plane. The contribution of spin-productive scattering events is below 5%. If the electron spin at incidence is chosen to be perpendicular to M, it rotates into the direction of M and also precesses around it. [S0031-9007(98)07521-8] PACS numbers: 73.50.Yg, 79.20.Kz The application of polarized electron beams to the study of magnetism took its beginning when the first spinpolarized electrons were obtained by photoemission from magnetic materials [1]. The most obvious way of looking at photoemission of electrons theoretically is to assume that the fast photoelectron does not interact appreciably with the other electrons in the metal so that the photoemission experiment often is thought of as measuring the energy spectrum of its own hole state left behind. This theory of renormalized one-electron states has been discussed in the present context by Anderson [2], Doniach [3], Gutzwiler [4], and many others [5]. However, it could never explain the fact that no negative spin polarization is detected in photoemission from states near the Fermi energy E F in Co [6,7]. This and many other features observed in emission of low energy electrons from transition metals are now understood by considering the scattering of the excited electron on the partially filled d states of all of the atoms encountered in transport through the transition metal [8]. To study this important phenomenon more thoroughly, we have measured the total scattering cross section as a function of electron energy. In contrast to numerous earlier investigations [9], we have observed very large transmission asymmetries A of up to 80% with an electron beam passing through a thin ferromagnet depending on whether its spin is parallel or antiparallel to the magnetization M. Furthermore, when the spin polarization vector P 0 of the incident electron beam is chosen to be perpendicular to M, then it rotates into the direction of M and simultaneously also precesses around M. There is a complete analogy to the magneto-optic phenomena observed when a light beam passes through ferromagnetic material. But, even when measured on the length scale of the penetration depth, the magneto-"optic" effects observed with electron beams are at least 1 order of magnitude larger as compared to those observed with light beams. This arises because the electron beam couples directly to the magnetization, while the coupling of the light beam must be mediated by the spin-orbit interaction. The observations presented here have a number of immediate important implications. For instance, the scattering cross section governs the nonequilibrium magnetization dynamics which is presently at the forefront of fundamental research in magnetism [10][11][12][13]. Furthermore, experiments of the type described here might help to improve the performance of spin filters, spin ...
If electrons are reflected from a ferromagnet, the spin moves depending on the magnetization vector of the ferromagnetic surface. The spin motion, consisting of a precession around the magnetization direction and a rotation into it, is measured and explained in terms of the electronic band structure of the ferromagnet. If applications within a solid-state device are considered, sizeable transverse torques on the magnetization due to the spin precession can be expected.
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