MAGNONS TRANSMISSION THROUGH AN ATOMIC WIRE CONNECTING TWO ULTRATHIN HEISENBERG FERROMAGNETS

Abstract

The magnons transport properties of molecular wires connecting two Heisenberg ferromagnets are studied within the framework of the matching method and with use of a realistic atomic structure. The model system consists of two nanostructured ferromagnetic films on either side of the junction and the atomic wire consists of a linear molecule connecting two ultrathin solid ferromagnetic films. A theoretical model is presented for the study of the transmission and the reflection of spin waves at the atomic wire junction. The calculation was made at the atomic scale for two identical waveguides with ordered spins and coupled by Heisenberg exchange interaction between first neighbors. Our analysis yields a detailed understanding of the spin-wave coherent scattering at the linear molecular junction. We calculate, in particular, the coherent reflection R and transmission T coefficients, which constitute the elements of the scattering matrix in accordance with the Landauer–Büttiker scattering formalism, as well as the magnon transmittance of the atomic wire for spin-waves incident from the interior of the film on the junction. The most representative numerical results obtained for the system of two slabs made up of three Fe ferromagnetic atomic layers connected with an Fe or Gd atomic wire are presented as function of the dimensionless frequency Ω in the magnons energy band. The coherent reflection and transmission scattering cross sections show characteristic spectral features, depending on the length of the wire, on the cut-off frequencies for the propagating magnons, as well as on the magnons incidence angle. The results illustrate the occurrence of Fano resonances in the transmitted spectra due to the interaction of localized spin states on the atomic wire with the propagating spin waves of the waveguide. An interesting physical effect is observed for this magnetic atomic junction, namely the frequency selective conductance of the spin waves via Fano resonances, by an appropriate choice of the spin-wave incident angle.