Emergence of the stripe-domain phase in patterned Permalloy films

TL;DR

This paper investigates the transition from homogeneous to stripe-domain magnetic configurations in Permalloy films, revealing an intermediate emerging stripe-domains regime characterized by domain-wall changes and magnetoresistance broadening.

Contribution

It identifies and characterizes an intermediate emerging stripe-domains regime in Permalloy films, expanding understanding of magnetic phase transitions with respect to film thickness.

Findings

Discovery of an intermediate ESD regime below critical thickness

Broadening of magnetoresistance dip signals ESD transition

Sharp increase in magnetoresistance ratio marks stripe formation

Abstract

The occurrence of stripe domains in ferromagnetic Permalloy (Py=Fe$_{20}$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-domains (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-domains (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.