1052 THE BELL SYSTEM TECHNICAL JOURNAL, SEPTEMBER 1954 



from ferromagnetic resonance data' or from the conductivity of Fe304 . 

 The above method of calculating r from domain wall data is less sat- 

 isfactory at room temperature. 



The idea of associating losses in ferrites such as this one with 

 changes of order in the divalent and trivalent iron ions explains the fact 

 that the damping obser\^ed in domain walls at room temperatuie in 

 Fe304 , where none of the divalent iron is replaced by nickel, is larger 

 than that observed in (NiO)o.75(FeO)o.25Fe203 . Finally, as Wijn and van 

 der Heide^' have pointed out, and as (31) and (33) show more analyti- 

 call}^, this mechanism is a very satisfactory explanation of the sharp 

 change in domain wall relaxation frequency observed by Gait, Matthias, 

 and Remeika.^^ 



ACKNOWLEDGEMENTS 



The author wishes to express his gratitude to many friends and col- 

 leagues for assistance with various aspects of this research. The crystals 

 from which these samples were cut were obtained through Dr. G. W. 

 Clark from the Linde Air Products Co. H. J. Williams has been of 

 considerable help in observing the domain patterns. Most of the work of 

 cutting the samples from bulk crystal and preparing them was done by 

 J. A. Andrus, Mrs. M. R. Tiner, and R. E. Enz. The hysteresis loops 

 were taken in collaboration with P. P. Cioffi and F. J. Dempsey. The 

 special pulser used in obtaining the data was designed by H. R. Moore 

 and built by H. G. Hopper. The chemical analyses were made by H. E. 

 Johnson, J. F. Jensen, and J. P. Wright. Enlightening discussions were 

 had with J. F. Dillon, Jr., C. Herring, A. N. Holden, B. T. Matthias, 

 W, T. Read, H. J. Williams, and A. M. Clogston, who derived inde- 

 pendently a result somewhat similar to that in (31). Useful comments 

 were made on the manuscript by R. M. Bozorth, S. INIillman and P. W. 

 Anderson. 



REFERENCES 



1. Ratio, Wright and Emerson, Phvs. Rev., 80, p. 273, 1950. Rado, Wright, Emer- 



son and Terris, Phvs. Rev., 88, p. 909, 1952. G. T. Rado, Revs. Mod. Phvs., 

 25, p. 81, 1953. Welch, Nicks, Fairweather and Roberts, Phvs. Rev., 77, p. 

 403, 19.50. 



2. D. Polder and J. Smit, Revs. Mod. Phvs., 25, p. 89, 1953. J. J. Went and H. P. J. 



Wijn, I'hvs. Rev., 82, }). 269, 1951. Wijn, Gevers and van der Burgt, Revs. 

 Mod. Phvs., 25, p. 91 , 1953. H. P. J. Wijn and H. van der Heide, Revs. Mod. 

 Phvs., 25, p. 98, 1953. H. P. J. Wijn, Thesis, Leiden, 1953. Separaat 2092, 

 N. V. Philips Gloeilampenfabrieken, Eindhoven, Holland. 



3. H. J. Williams, Phvs. Rev., 52, p. 7-47, 1937. H. J. Williams and W. Shockley, 



I'hys. Rev., 75, p. 178, 1949. Williams, Bozorth and Shockley, Phys. Rev., 



