Regensburg 2004 – wissenschaftliches Programm

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MA: Magnetismus

MA 27: Spinabh
ängiger Transport II

MA 27.12: Vortrag

Donnerstag, 11. März 2004, 18:00–18:15, H22

Magnon-assisted transport due to itinerant electron exchange scattering in ferromagnetic tunnel junctions — •Grigory Tkachov — Institute for Theoretical Physics, Regensburg University, 93040 Regensburg, Germany

We propose an itinerant electron model for inelastic tunneling spectra of ferromagnetic junctions observed in recent experiments [1]. In our approach the exchange (Fock) part of the Coulomb interaction between electrons with opposite spins is used to derive a transfer Hamiltonian describing single-electron tunneling with a simultaneous spin flip [2]. In such an inelastic process a tunneling electron (e.g. a spin-up one) excites an electron from a "spin-downNo-dq Fermi sea of the other ferromagnet into an empty state above the Fermi level while substituting the latter inside the "spin-downNo-dq Fermi sea. These exchange-induced spin flips can be treated as a collective spin excitation of the Fermi sea electrons. Since the electron-magnon coupling is mediated by the Coulomb potential, the tunneling matrix elements of the inelastic current depend on the magnon wave-vector and, therefore, on its energy. This dependence can explain strongly non-monotonous inelastic tunneling spectra measured in Refs.[1].

[1] J.S. Moodera, J. Nowak, and R.J.M. van de Veerdonk, Phys.Rev.Lett. 80, 2941 (1998); Y. Ando, J. Murai, H. Kubota, and T. Miyazaki, J. Appl. Phys. 87, 5209 (2000); J.H. Yu, H.M. Lee, Y. Ando, and T. Miyazaki, Appl. Phys. Lett. 82, 4735 (2003).

[2] S. Zhang, P.M. Levy, A.C. Marley, and S.S.P. Parkin, Phys.Rev.Lett. 79, 3744 (1997).