1028 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



•0.8 -0.6 -0.4 



-0.2 O 0.2 0.4 



H IN OERSTEDS 



Fig. 2 — Hysteresis loop taken on sample before heat treatment in a magnetic 

 field. 



preparing the samples for observing their domain pattern and for per- 

 forming our experiments on them. 



Four samples have been prepared in this way for our studies on 

 (NiO)o.75 (FeO)o.25 FesOs . 



Domain Pattern Observations 



The method used to observe the domain walls on these surfaces is 

 the same as that used by Williams and his collaborators. We will there- 

 fore not describe it in detail. It consists essentially of observing through 

 a microscope the pattern formed by a magnetic colloid on the surface. 



The observation of domain patterns, even on these carefully pre- 

 pared samples, is difficult. There is still some pitting on the surfaces. 

 Also, many of the surfaces become rounded in the process of polishing. 

 This produces surface spikes of the sort discussed by Williams, Bozorth 

 and Shockley.^ The result is that on many surfaces the domain pattern 

 of the sample as a whole has to be discerned in a substantial amount 



