MFM and FORC+ study of switching mechanism in Co$_{25}$Pd$_{75}$ films

TL;DR

This study investigates the switching mechanism in Co$_{25}$Pd$_{75}$ films with perpendicular magnetic anisotropy using MFM and FORC techniques, revealing domain nucleation and dendritic growth as key processes.

Contribution

It introduces a combined MFM and FORC methodology to analyze the switching mechanism in CoPd films, providing new insights into domain behavior during magnetization reversal.

Findings

Switching occurs via domain nucleation and dendritic growth.

Unreversed domains shrink into small dots before disappearing.

MFM and FORC effectively reveal the switching process.

Abstract

Recent research on CoPd alloys with perpendicular magnetic anisotropy (PMA) has suggested that they might be useful as the pinning layer in CoFeB/MgO-based perpendicular magnetic tunnel junctions (pMTJ's) for various spintronic applications such as spin-torque transfer random access memory (STT-RAM). We have previously studied the effect of seed layer and composition on the structure (by XRD, SEM, AFM and TEM) and performance (coercivity) of these CoPd films. These films do not switch coherently, so the coercivity is determined by the details of the switching mechanism, which was not studied in our previous paper. In the present paper, we show that information can be obtained about the switching mechanism from magnetic force microscopy (MFM) together with first order reversal curves (FORC), despite the fact that MFM can only be used at zero field. We find that these films switch by a mechanism of domain nucleation and dendritic growth into a labyrinthine structure, after which the unreversed domains gradually shrink to small dots and then disappear.