Figure 4
Illustration: Alan Stonebraker

Figure 4: Domain walls in a ferromagnet. (a) Bloch walls where the spins rotate in a plane perpendicular to Q are in most cases not ferroelectric. (b) The spin rotation across a NĂ©el wall is similar to the cycloidal spiral in Fig. 3(c), and, by Eq. (1), it will develop a spontaneous polarization P localized at the domain wall. (c) If now one puts such a wall in the gradient of an electric field, it will be pulled in or pushed out of the region of stronger field, depending on the sign of its dipole moment [36].