Wall motion and rotational magnetization in thin permalloy films

Abstract

Dynamic and nearly static magnetization reversal mechanisms in thin permalloy films are investigated experimentally using pulse techniques and vector locus configurations. At least for the driving field strength used, easy-axis switching waveforms indicate that wall motion is predominant when no transverse field is applied. At a given transverse bias field, the simultaneous pick-up signals from aligned and crossed loops show that the voltage-time integral at zero crossing time of the transverse signal becomes dominant for increasing drive field. The complicated irreversible magnetization phenomena on the astroid are illustrated experimentally on the coordinate system by the vector locus for a 10 kc/s sinusoidal driving field and pulse field having 0.5 ns rise-time. Wall motion and rotation during flux reversal are clearly distinguished on these configurations for various combinations of externally applied fields. The critical angle for coherent rotation is in good agreement with that derived from the Stoner-Wohlfarth model at a 10 kc/s sinusoidal field. However, for excess driving pulse fields, the dynamic vector locus suggests that until the walls nucleate and start to move, the coherent rotation continues over the critical angle suggested by the astroid. This gives a clear answer as to the cause of the nonlinearity on the plots of the inverse reversal time vs. driving field with the transverse bias field as a parameter.