Dynamics of Magnetization Reversal: From Continuous to Patterned Ferromagnetic Films

Abstract

An overview on the dynamics of the field-induced magnetization reversal in ultrathin ferromagnetic films and in related laterally patterned nanostructures down to the nanosecond range is presented. The associated experimental techniques are briefly described. For quasi-perfect films, spin reversal is controlled by intrinsic nanostructural nucleation and pinning centers. Nucleation is thermally activated, and its rate varies exponentially with applied field H. For ultrathin films, domain walls propagate uniformly. When H is not large enough to overcome pinning energy barriers, the domain wall motion proceeds by successive thermally activated small jumps. When H is larger than the depinning force, a viscous wall motion with velocity linear in H is observed. A simple model is proposed to reconcile low and high field behaviors. More refined theoretical random field treatments and numerical simulations are presented. An alternative way is to analyze the data in terms of the movement of a 1-D interface in a disordered medium. The dynamics of the nucleation and domain wall processes are extensively investigated in a quasi-perfect Pt/Co(0.5 nm)/Pt film structure. Until now, few results on the dynamics of magnetization reversal in isolated submicron-sized magnetic elements arranged into periodic arrays are available. In this review, we report on the local and collective magnetic dynamic behavior and noncoupled or coupled dot arrays with out-of-plane anisotropy. In noninteracting dot arrays, reversal is controlled by the large distribution of local nucleation fields already present in the unpatterned film. As predicted theoretically, the dynamics of assemblies of coupled and noncoupled dots differ strongly.