Investigation of magnetic domain configuration and vortex-antivortex creation and annihilation on CoFeB patterns

Abstract

The characteristics of patterned CoFeB films have attracted much attention for spin configurations and magnetization processes of nanostructured elements in that CoFeB has desirable properties including magnetic softness, large magneto-impedance, high spin polarization, and epitaxial registry with MgO(100). In this experiment, micron-sized CoFeB islands with various thicknesses, deposited by a sputtering process, were investigated in order to study their slow micro-magnetic properties as a function of an externally applied magnetic field as well as their remanent domain configurations. Magnetic Force Microscopy (MFM) of the array at zero applied field revealed that despite a large variation in CoFeB thickness, the remanent domain configurations could be classified into several unique domain configurations. Selected islands of dimensions from 0.25µm x 0.25µm to 16µm x 16µm were studied using MFM equipment. In addition, the creation and annihilation of magnetic vortex and antivortex pairs in cross-tie walls on CoFeB islands of 16 µm x 4 µm were investigated using MFM in the presence of an applied field. The first vortex-antivortex pair 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 vortex-antivortex pair creation satisfies the condition that the closure domain vortices have the same chiralities. Pair annihilation was found to occur 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.