Plasma process induced physical damages on multilayered magnetic films for magnetic domain wall motion

The effect of ion irradiation on magnetic domain wall motion (DWM) in a perpendicularly magnetized Co/Ni multilayered film was investigated. The DWM in the Co/Ni multilayered film was sometimes inhibited owing to damage in Co/Ni induced by ion irradiation from Ar/NH3/CO plasma during the etching of the upper layer of a Co/Pt multilayered film depending on the etched depth over Co/Ni. When the DWM was disturbed, modifications of crystallinity were observed by transmission electron microscopy (TEM) near the etched surface region of Co/Ni. Also, the segregation of Pt which was knocked on from the upper layer of Co/Pt, was observed by energy dispersive X-ray line-scan analysis by TEM (TEM–EDX). In contrast to that, the sample which had fine DWM property showed clear lattice image of Co/Ni. A Monte Carlo simulation of Ar+ ion irradiation predicted an atom-displacement range of about 3.5 nm depth from the etching surface when the ion acceleration voltage was 900 V. It was deep enough to degrade the area near the top region of the Co/Ni multilayered magnetic thin film. Eliminating these physical modifications during the etching process would be the key to the fabrication of reliable nonvolatile devices using domain wall motion.