Emergence of the stripe-domain phase in patterned permalloy films

Abstract

The occurrence of stripe domains in ferromagnetic permalloy $(\mathrm{Py}={\mathrm{Fe}}_{20}{\mathrm{Ni}}_{80})$ is a well-known phenomenon which has been extensively observed and characterized. This peculiar magnetic configuration appears only in films with a thickness above a critical value $({d}_{cr})$, which is strongly determined by the sputtering conditions (i.e., deposition rate, temperature, magnetic field). So far, ${d}_{cr}$ has usually been presented as the boundary between the homogeneous (H) and stripe-domain (SD) regime, respectively, below and above ${d}_{cr}$. In this work we study the transition from the H to the SD regime in thin films and microstructured bridges of Py with different thicknesses. We find there is an intermediate regime, over a quite significant thickness range below ${d}_{cr}$, which is signaled in confined structures by a quickly changing domain-wall configuration and by a broadening of the magnetoresistance dip at the coercive field. We call this the emerging stripe-domain (ESD) regime. The transition from the ESD to the SD regime is accompanied by a sharp increase of the magnetoresistance ratio at the thickness where stripes appear in MFM.