MOTION OF ixnivinrAi. domain walls 



1031 



Fig. 5 — Picture of a section of the movable wall along one leg of sample. The 

 line has been slightly emphasized by retouching after the picture was taken. The 

 edge of the leg can be seen at the bottom of the figure. 



It is unlikely that the wall is so distorted from a plane when in rapid 

 motion, however, since then the driving force and the viscous damping 

 resistance to motion are both much larger than the effects of these 

 imperfections. The imperfections, of course, are primarily effective in 

 tietermining the coercive force, as read from the hysteresis loop. 



The domain pattern as traced out on each of four samples is discussed 

 below : 



Sample 1. Although they had spikes associated with them, the sta- 

 tionary walls expected at the corners could be seen, at least in part. In 

 addition, at one of the acute angle corners there was some rather ex- 

 tensive domain wall structure. This structure had one form when the 

 sample was magnetized in one direction, another when it was magnetized 

 in the other. It was due to the presence of a small void at this corner 

 whose magnetic energy was reduced by having domains of reversed 

 magnetization around it. The existence of this void was established from 

 stiiicture which {ippcared in the spots on an X-ray Laue photograph 

 taken at this point. The process of magnetization in this sample con- 

 sisted in (a) the growth of the wall from the nucleus around this void 

 imtil it existed all around the ring, and (b) the motion of this wall to 

 the other side of the sample, where it again shrank to a configuration 



