Influence of antiphase and ferroelastic domain boundaries on ferromagnetic domain wall width in multiferroic Ni-Mn-Ga compound

Abstract

This paper reports on the experimental measurements of magnetic domain wall (DW) widths by Lorentz transmission electron microscopy in Ni-Mn-Ga ferromagnetic shape memory alloys. The wall widths were measured and compared in both austenitic and martensitic states, at positions pinned on antiphase boundaries (APB) or coinciding with the twin boundaries (TB) together with walls at APB-free and TB-free positions. The thickest DW widths of about 28 nm were measured in APB-free positions in austenite. DW in APB-free and TB-free positions in martensite had widths of about 10 nm for in-plane and 13 nm for perpendicular easy axis orientation. The narrowest DWs with widths about 7–8 nm were measured for walls pinned on APBs in austenite or for walls coinciding with the TBs in martensite. The measurements are broadly in agreement with theoretical wall width predictions in thin foil.