Micromagnetic and MFM studies of a domain wall in thick {1 1 0} FeSi

Abstract

A 180° domain wall on a {1 1 0} surface of a 0.3 mm thick crystal of FeSi (3.25% Si), and containing a Bloch line, has been studied by magnetic force microscopy (MFM) with particular attention to disturbance by the probe. A technique for distinguishing the contributions to the MFM signal arising from the undisturbed structure and from the disturbance to that structure, by repeating the observations with probe moment reversed, is discussed. Valid to first order, and applicable only to mild reversible perturbations, it is used to compare the observed wall structure with that of a micromagnetic model. Asymmetry in the MFM signal is consistent with the presence of a Néel cap that closes the flux to one side of the wall at the surface. Scanning by the probe sometimes created (or destroyed) kinks in attractive wall sections. These kinks are identified as junctions between lengths of wall having a common Bloch core but opposite Néel cap orientations. Comparison is made with a micromagnetic model of such a kink. The kinks and the Bloch line could be moved by scanning, depending on the polarisation and flying height of the tip.