Rabi oscillations in the spin-dependent quantum conductance under modulated magnetic fields: application to domain walls in magnetic nanowires.

FERNANDEZ, LUCAS JONATAN; HORACIO M. PASTAWSKI

Rosario, Santa Fé

Congreso; Reunión Nacional de Sólidos 2013; 2013

IFIR - CONICET

We describe the spin-dependent quantum conductance in a wire where the magnetic field is spatially modulated. We apply this formulation to a ferromagnetic nanowire with a domain wall (DW) where the local field varies smoothly both in direction and intensity. Since the magnetization at the domain imposes a spin quantization direction, its perpendicular component inside the DW act as a perturbation that mixes spin projections. We identify two striking diabatic regimes that depend on the magnitude of the field inside the DW as compared with that in the domains. 1) If the intesity is weak enough (head-to-head DW) the local Zeeman energies result in an avoided crossing. Thus, the spin flip probability follows the Landau-Zener formula. 2) For a strong transverse field (Neel DW), the spin-dependent conductance shows oscillations as function of the DW width. We interpret them in terms of Rabi oscillations. Time and length scales obtained from this simplified view show an excellent agreement with the exact dynamical solution of the spin-dependent transport. We introduce and solve a model for spatially continuous dephasing that extends the D'Amato-Pastawski model. It allows us to show that Rabi oscillations are not particularly sensitive to decoherence. These results remain valid for other situations involving modulated magnetic structures and thus they open new prospects for the use of quantum interferences in spin based devices.