Structure of Subdivided Bloch Walls

The subdivision of Bloch walls into periodic right- and left-handed Bloch segments observed by Williams and Goertz, by DeBlois and Graham, and recently by Harrington is shown to be caused by screw rotation of the spin; not only along the width of the wall, but also along the length of the wall with different periodicity. The width of the wall and the distance between the right-handed and left-handed segments are determined by an approximate minimization of the total energy of the wall which is composed of exchange, anisotropy, and magnetostatic energies. These values agree well with the experimental results. The spin structure of this complex wall gives rise, out of itself, to right- and left-handed Bloch segments and the positive and negative Néel segments. The zig-zagging of the wall under externally applied field, observed by DeBlois and Graham, is also explained.