ELFT HÍRADÓ

[udvardi AT bolyai.phy.bme.hu (Udvardi Laszlo)]

                                 MEGH'IV'O
               A Budapesti Muszaki Egyetem, Fizikai Int'ezet
                    Elm'eleti Fizika Tansz'ek tudom'anyos
                              szemin'arium'ara

                                   T'ema:
              Spin Transfer in Ferromagnet-Normal Metal Systems

                                  El"oad'o:

                                Arne Brataas
                             Department of Physics
               Norwegian University of Science and Technology
                                 Trondheim


            Id"opont: 2002. december 13.-'an  10.15 'ora

   Hely :     Budafoki 'ut 8 (F-'ep"ulet, III. lh., mfsz.,
                      Szemin'ariumi szoba

            Minden 'erdekl"od"ot sz'i vesen l'atunk !


                        Udvardi La'szlo'

Abstract: 

 Mesoscopic ferromagnet-normal metal systems have recently attracted
considerable attention. Slonczewski and Berger proposed that a spin-
current could cause a switching of the magnetization orientation. The
idea is that the spin-current induces a torque, a "spin-torque", on the
spins of the conduction electrons, which subsequently transmit this
torque to the magnetization. We formulate a theory of spin dependent
transport of an electronic circuit involving ferromagnetic elements with
non-collinear magnetizations which is based on the conservation of spin
and charge current. The theory considerably simplifies the calculation
of the transport properties of complicated ferromagnet-normal metal
systems. We illustrate the theory by computing the spin-torque in three-
terminal systems with diffusive, tunnel and ballistic junctions. We
demonstrate that there is also a reverse mechanism: Precessing
ferromagnets are predicted to inject a spin current into adjacant
conductors. This opens the way to create a pure spin source "spin
battery" by ferromagnetic resonance. When the normal metal is a spin
sink this "pumping" of spins slows down the precession corresponding to
an enhanced Gilbert damping constant in the Landau-Lifshitz equation.
Our estimates for permalloy thin films explain the trends observed in
recent experiments.