Regensburg 2010 – scientific programme
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MA: Fachverband Magnetismus
MA 14: Spin Dynamics / Spin Torque I
MA 14.7: Talk
Wednesday, March 24, 2010, 11:15–11:30, H10
Extension of Yafet’s theory of spin relaxation to ferromagnets — •Christian Illg1, Daniel Steiauf2, and Manfred Fähnle1 — 1Max-Planck-Institut für Metallforschung, Heisenbergstraße 3, 70569 Stuttgart, Germany — 2Materials Department, University of California, Santa Barbara, CA 93106-5050, USA
By making use of Kramer’s degeneracy of the electronic states in a nonmagnetic material, Yafet [1] has derived an expression for the longitudinal spin relaxation time T1 due to scattering of electrons at phonons in the presence of spin-orbit coupling, using rate equations near the equilibrium state and Fermi’s golden rule for the scattering rates.
This expression involves the properties of electronic and phononic states and the matrix elements for the scattering. In a ferromagnet, Kramer’s degeneracy does not hold and then the electronic dispersion and density of states become spin-dependent. Moreover, the symmetry of the scattering matrix element changes. It is shown that an analogous (yet more complicated) expression for T1 can be derived for ferromagnets when taking into account the conservation of the total number of electrons. This expression can be used as a starting point for the ab-initio calculation of T1, and this quantity is required for an interpretation of the ultrafast demagnetization of ferromagnets after excitation with a femtosecond laser pulse.
Y. Yafet, in Solid State Physics (Eds.: F. Seitz and D. Turnbull, Academic, New York, 1963), Vol. 14.