Domain-wall motion in thin permalloy films in pulsed magnetic field

The behavior of a separate 180-degree domain wall subjected to the action of a pulse magnetic field is investigated in Permalloy films of the thickness range of 260-4000 Å. The nature of the wall motion is strongly dependent on the accuracy of adjusting the direction of the field relative to the easy axis. In respect to the type of dependence of the wall velocity on the pulse-field amplitude
H
, studied films may be divided into four groups. In two groups there is a nonlinear dependence
\upsilon(H)
, the main dynamic characteristic of which should be the second coefficient of mobility
G"
measured at a comparatively high velocity. In the thickness region of 700-900 Å, the mobility
G"
has a clearly defined minimum caused by the high crosstie density. The possibility of calculating the spin-damping coefficient α from data on domain-wall mobility is discussed. The use of conventional formulas derived for the unidimensional domain wall leads to α values nearly 10 times higher than α
r
calculated from the width of the ferromagnetic resonance line. It is concluded that in the film thickness range of 400-900 Å and in thicker films it is still impossible to calculate the spin-damping factor α from data of domain-wall mobility because the complicated wall structure should be taken into account.