Vortex-antivortex creation and annihilation on CoFeB crosstie patterns

Abstract

The creation and annihilation of vortex and antivortex pairs in crosstie walls on CoFeB islands were investigated using magnetic force microscopy (MFM) in the presence of applied field. The first vortex-antivortex pair (V-AV) is nucleated in a 4-domain Landau pattern from a section of a 180° degree Néel wall as a consequence of the formation of an end domain closure pattern. The V-AV pair creation satisfies the condition for the closure domain vortices to have the same chiralities. Pair annihilation occurs in two steps: a rapid advance of the vortices toward the more or less fixed antivortices followed by a deceleration caused by the decrease in local susceptibility. There is a spread in the annihilation fields that does not depend upon the core polarity but is determined by energy minimization.