MAGNETIZATION REVERSAL IN ULTRATHIN FERROMAGNETIC-FILMS WITH PERPENDICULAR ANISOTROPY

This paper presents a detailed study of the magnetization reversal dyn amics in ultrathin cobalt films (t(Co) = 6-12 Angstrom) sandwiched by gold (1 1 1) layers, their magnetic anisotropy being perpendicular to the film surface. The domain wall (DW) velocity and nucleation rate ar e determined from direct time-resolved domain structure imaging. Measu rements as a function of the applied magnetic field and temperature en able us to estimate the magnetic parameters, such as activation volume s, coercive fields, Gilbert damping parameters, etc., controlling the magnetization reversal. Depending upon the applied magnetic field valu e three different regimes are evidenced and studied. Al low fields the DW pinning by structural inhomogeneities controls the thermally activ ated magnetization reversal dynamics. Above the propagation held value the dynamics is due to viscous DW motion. In higher fields a DW veloc ity breakdown is observed. The DW jaggedness and its change with the a pplied field and temperature is examined through the DW fractal dimens ion. A simple DW motion simulation taking into account an activation v olume distribution explains qualitatively the data.