Magnetic thin film domain wall motion under dynamic fields

Abstract

Previous computer simulation models are utilized to study two-dimensional domain wall motion in submicron thin permalloy films driven by in-plane sinusoidal fields. Under suitable ac fields applied in the easy direction, the wall motion is periodic and regular, yielding a phase lag in magnetization response giving the same effective wall mass as obtained previously from pulse fields. With a hard axis ac field, rich patterns of wall motions are observed, in contrast to a dc hard axis field. Unlike wall creep, a small dynamic hard axis field alone is sufficient to drive the wall in the film thickness direction or along the hard axis (wall streaming or worm motion). Accompanying this motion, wall structure transitions between Bloch and Néel may also take place, depending on both the amplitude and the frequency of the applied field. Such transitions are more favorable for larger amplitude and lower frequency fields. The frequency dependence of the magnetization response of a domain wall to a transverse field may also be characterized by approximate scalings of the hysteresis loops. At frequencies up to 500 MHz, the domain magnetization is conducted by wall motion, wall structure transition or a combination of both; whereas at higher frequencies, these effects are largely suppressed.