1024 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



magnetization in such materials. In the ferromagnetic metals, it is well 

 known that these losses ordinarily arise largely from the eddy currents 

 which are induced by the motion of the domain walls. In the ferrites, 

 however, the conductivity is so low that the contribution of eddy cur- 

 rents to the losses is never overwhelming and is often negligible; the 

 losses must therefore in large part arise from other sources not yet under- 

 stood. It is the purpose of this paper to present some recent studies of 

 these losses and to discuss their relevance to the losses in ferrites gen- 

 erally. 



In any ordinary sample of a ferromagnetic material, a study of domain 

 wall motion and the associated energy losses is complicated by the fact 

 that the domain pattern is very complex. Any attempt to provide a 

 theoretical explanation of data taken on such samples must invoh^e an 

 averaging process over many domain walls of varying area, crystal 

 orientation, etc. This makes it extremely difficult to describe the be- 

 havior of such patterns uniquely and quantitatively, although some 

 progress has been made. ' A method of avoiding this difficulty has been 

 developed by Williams, Bozorth, Shockley, Kittel and Stewart '^ in 

 working on silicon iron. This method consists in cutting a polygonal 

 ring from a single crystal in such a way that each leg of the ring lies 

 along one of the easy directions of magnetization in the crystal. In 

 silicon iron this leads to a rectangular ring with each leg along a [100] 

 crystal direction. In the ferrite which we use this technique to study 

 here, the easy directions are [111] directions, and we use a diamond 

 shaped sample as shown by the solid lines in Fig. 1. Each leg is along a 

 [111] direction, and the major face is a (110) plane. If the sample is good 

 enough, the domain pattern is that indicated by the dotted lines in Fig. 

 1. This pattern consists of four stationary walls, one at each corner, and 

 one movable wall which goes all the way around the sample. The mag- 

 netization thus travels around the sample in two paths, one clockwise 

 and the other counter-clockwise, and the position of the movable wall 

 therefore determines the net circumferential magnetization. In such 

 samples we study quantitatively and in some detail the motion of an 

 individual movable wall. 



Williams, Shockley and Kittef studied the motion of the movable 

 wall on one of the rectangles cut from a single crystal of silicon iron. 

 They found the motion to be viscously damped, as Sixtus and Tonks 

 had in earlier experiments with more complicated domain walls. I^e- 

 cause of the simplicity of their domain pattern, Williams, Shockley and 

 Kittel were able to cak^ulate the eddy current losses in their experi- 

 ments, and to show that they accounted for most of the observed damp- 



