Cooperative motion of domain walls in magnetic multilayers

It is well known that the sequence of induced emf spikes in a Barkhausen spectrum bears no resemblance to the sequence of spikes in successive field cycles; in general, no two spectra are ever alike. The present study reports the observation of remarkably reproducible Barkhausen spectra over repeated field cycling in TbFe/FeCo exchange spring multilayers. Their reproducibility is shown to have origins in the highly synchronized and cooperative motion of domain walls in different layers. Whereas a handful of previous studies have shown limited reproducibility in small field excursions, in small samples, or over small distances, the reproducibility of magnetic avalanches in the present study occurs along the entire major magnetization loop, and the emf avalanches can be reproducibly transmitted over macroscopic distances (∼1 cm). The complexity of these highly reproducible spectra varies with the in-plane field direction, and reveals a new mode of magnetization reversal along the hard axis. Results also provide an avenue for information transmission over macroscopic distances in a magnetic medium.