New Method to Measure Directly the 180° Bloch Wall Energy

Abstract

Using the Bitter technique, the traces of a single 180° Bloch wall are observed by a device composed of two microscopes, one on each side of the sample. The wall is twisted by an inhomogeneous magnetic field. The measured displacements of the wall traces are related to the surface energy γ0 of the Bloch wall which in turn is related to the Heisenberg exchange constant A. In an iron-silicon alloy with 3% Si we find γ0=1.48 ergs/cm2 and A=1.48×10−6 ergs/cm at room temperature, in fair agreement with the value A∼1.7×10−6 ergs/cm derived from Bloch's law and spin-wave theory at 0°K.