Neel wall

Domain wall structures in thin films and small particles can be different from those in massive samples, because some energy contributions may become significant when sample dimensions are decreased. In thin films, the magnetisation vector tends to remain parallel to the film plane to avoid any contribution to the magnetostatic energy. The spins within a domain wall also rotate within the film plane, which leads to Neel walls. Fig. 4.31. Neel walls appear in thin films below a critical thickness limit. 

Fig. 4.31. A Neel wall. Spin rotation within the wall occurs without external magnetic flux (schematic).

Neel walls, twist- and tilt-reverses are the three major disclinations in actual LCDs. A Neel wall disclination may be caused by weak azimuthal anchoring. A twist-reverse is a defect in which the twist direction is opposite to the chirality of the added chiral agent. A tilt-reverse is a defect in which the inclination direction induced by applying a voltage is the opposite of the intended direction. These tilt-reverse defects may be caused by the lateral electric field generated by the fringe field of the pixel electrodes. 

Deposition of metachromatio material in tissues other than the central nervous system was noted quite early by Witte (1921) in the anterior lobe of the pituitary and in liver, renal tubuli and testes by Norman (1947) in the gallbladder wall and renal tubuli, and by Einarson and Neel (1942) in the kidneys. In a case described by Kaltenbach (1922), hepatosplenomegaly was found at autopsy, but metachromasia was not looked for. 

Figure 14. Distribution of directors at an interface presenting a constant anchoring angle (as in Fig. 12) and around the extremity of a thin thread, with patterns (as in Fig. 10). A discontinuity line appears unavoidably at the interface and is attached to the core of the defect. In the bulk, these lines create Neel or Bloch walls, or hybrid textures.

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