THE BELL SYSTEM 



TECHNICAL JOURNAL 



VOLUME XXXIII tf ETT i;.M H I;H 1954 numbers 



Copyright, 1954, American Telephone and Telegraph Company 



Motion of Individual Domain Walls in a 

 Nickel-Iron Ferrite 



By J. K. GALT 



(Manuscript received May 11, 1954) 



Samples have been cut from single crystals of the nickel-iron ferrite 

 (Xi())(i.75 (FeO)o. 25^6203 in such a way that they contain one and only one 

 movable ferromagnetic domain wall. The viscous damping coefficient for 

 this wall, which is a measure of the losses associated with domain wall 

 motion in this material, has been measured as a function of temperature. 

 This damping shows a very large increase as the temperature goes down to 

 the region of 77°K. The value of this damping is correlated with the Landau- 

 Lifshitz equation for the rotational motion of magnetization by means of 

 previously available theoretical analysis. In addition, it is suggested that 

 the sharp increase in damping at low temperatures is due to a relaxation 

 associated with a rearrangement of the valence electrons on the divalent and 

 trivalent iron ions in the ferrite. A tentative phenomenological theory of the 

 losses based on this mechanism is presented. 



INTRODUCTION 



The mechanism which contributes most to the permeabihty of high- 

 permeability magnetic materials is the motion of ferromagnetic domain 

 walls. These walls are thin lamellae in which the direction of the spon- 

 taneous magnetization of the material changes from one domain to 

 another. As a result, this mechanism contributes a major part of the 

 energy losses whir'h accompany rapid changes in th(> direction of the 



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