The dynamical behavior of magnetic domain walls and magnetic bubbles in single-, double-, and triple-layer garnet films

Abstract

The dynamical behavior of straight magnetic domain walls and propagating magnetic bubbles in single-, double-, and triple-layer lanthanum gallium garnet films is reported. In the study of straight walls in the single-layer films, a good agreement is obtained between the observed and the calculated values of the domain-wall width parameter Δ, the derivative of the peak velocity to in-plane field at high in-plane fields, and the derivative of the saturation velocity to in-plane field at a moderate drive field and high in-plane fields H1. The saturation velocity (at H1=0) decreases with decreasing film thickness, which is in disagreement with theoretical predictions. A propagating bubble in a single-layer film exhibits an overshoot. In double- and triple-layer films, the observed and calculated Δ values disagree in most cases, and the straight wall and propagating bubble saturation velocities are significantly higher than in single-layer films. Overshoots and low-frequency oscillations are observed in the saturation regime of straight walls. The resulting high wall masses are attributed to stacking of horizontal Bloch lines on the film surface(s). From the measurements in in-plane fields, we conclude that the saturation velocity and the peak velocity in a double- and a triple-layer film depend on the polarity of the in-plane field, which is always perpendicular to the straight wall. It is found that the saturation region in double- and triple-layer films can be subdivided in three parts. This is explained qualitatively, and a calculation is made of the saturation velocity in double- and triple-layer films. This calculation shows good agreement with experimental results.

10.1007/s11451-008-2001-4

“…In [139], the rocking technique was used to study bubble domains; the data obtained in fields H p < 8M applied along the driving gradient field were in qualitative agreement with the V m (H p ) dependence calculated numerically in [137]. The dynamics of a straight DW in a field H p applied perpendicular to the DW plane was studied in [134] on a (Y,La) 3 (Fe,Ge) 5 O 12 film; for H p > 8M, the experimentally measured derivative dV m /dH p was found to be close to the coefficient π∆γ/2. However, no conclusion can be drawn from the experimental data concerning the mechanism of steady-state motion breakdown because the velocity V m ~ 65 m/s as determined in the lowest of the fields used (H p = 0.06H A ) is far higher than the limiting velocities derived within both the 1D and 2D models.…”

“…If the field applied in the film plane is strong (H p > 8M), then rigorous analysis gives a field dependence of the type V m ~ H p in both the cases where the field H p is parallel to the DW plane [51,128,[131][132][133] and perpendicular to this plane [115,130]. In the case where the strong field applied perpendicular to the DW plane (H p ӷ 8M) exceeds the stray field of surface charges and suppresses twisting of spins, we have [134] …”

“…The mass m eff should increase if the DW contain HBLs [46]. Perhaps, this fact explains low-frequency oscillations of DWs observed in [134] in multilayer garnet films.…”

“…Using the 1D model, it was shown in [140] that, if the DW is parallel to the easy axis of additional anisotropy, its [135]): (I) experimental data, (1) calculations using a formula from [127] with a field H p applied along the normal to the DW plane, (2) calculations using formulas from [107,127] with a field H p applied along the DW plane, (3) calculations using a formula from [128], (4) calculations using a formula from [134], and (5) fitting of the experimental data by a linear relation. maximum velocity increases with the constant K p of this anisotropy and is greater than the velocity of the DW oriented perpendicular to the easy axis.…”

“…Experimental data were taken from [98,121,134,[162][163][164][165][166] and were the most reliable, because the measurements reported in those papers were made using either dynamic bubble collapse or expanding bubbles and stripe domains using highspeed photography; furthermore, the required film characteristics were also reported in those papers. The data obtained by the bubble translation method were not used, because such measurements were performed in low fields H and, perhaps, did not correspond to the saturation region.…”