MOTION' OF INDIVIDVAL DOMAIN WALLS 1053 



75, p. 155, 1940. Williams, Sliorklcv and Kittel, Phys. Hov., 80, j). 1()!K), llC)!). 

 H. J. Williams, HoU Lahs. Kcconl 30, p. 385, 1952. 

 3a. K. H. Stewart, Vvov. Plus. Soc, 63A. p. TGI, 1950 and J. IMivs. ct Hadium, 

 12, p. 325, 1951. 



4. K. J. Sixtus and L. Tonks, Phys. Rev., 42, p. 419, 1932. 



5. W. A. Yager and R. M. Bozorth, Phys. Rev., 72, p. SO, 1947. 



6. L. Landau and E. Lifshitz, Physik. Z. Sowjctunion, 8, i). 153, 1935. 



7. J. K. Gait, Phys. Rev., 85, p. G64, 1952. 



8. Gait, Andrus and Hopper, Revs. Mod. Phys., 25, ]). 93, 1953. 



9. W. L. Bond, Phys. Rev., 78, p. 646, 1950, Abstract I 10. 



10. P. P. Cioffi, Phys. Rev., 67, p. 200, 1945 and Rev. Sci. Instr., 21, p. 624, 1950. 



11. P. Weiss and R. Forrer, Ann. Phys., Series 10, 12, p. 279, 1929. After the pres- 



ent work was completed, the author became aware of the extensive measure- 

 ments of Pauthenet (Ann. Phys., Series 12, 7, j). 710, 1952) on Ms in nickel 

 ferrite and magnetite, among other materials. Interpolation between Pau- 

 thenet's values for these two materials suggests that the value of Ms we have 

 used for (NiO)o.75 (FeO)o.25 Fe^Os is about 6% too high at 445°K and 3% too 

 low at 77°K, with intermediate errors between these temperatures and room 

 temperature. Since, however, the accuracy of our data is not significantly 

 better than this, and since our conclusions would be unaffected by any such 

 changes, no correction has been made to our data. 



12. R. Becker, J. Phys. et Radium, 12, p. 332, 1951. 



13. C. Kittel, Phys. Rev., 80, p. 918, 1950; J. Phys. et Radium, 12, p. 291, 1951. 



14. C. Kittel, Revs. Mod. Phys., 21, p. 541, 1949. See Eciuation 3.3.9. Since a wall 



perpendicular to the [100] direction in a crystal with a positive anisotropy 

 energy constant is discussed in this reference, g(5o) = and is left out. The 

 author is grateful to A. M. Clogston for pointing out the need for it in the 

 present research. It was ignored in References 7 and 8 with the result that 

 the values given for X in those references were somewhat in error. Correct val- 

 ues are given in Table I. 



15. E. J. W. Verwey and J. H. de Boer, Rec. Trav. Chim., 55, p. 531, 1936. E. J. W, 



Verwey and P. W. Haa^-mann, Physica, 8, p. 979, 1941. Verwey, Haaymann 

 and Romeijn, J. Chem. Phys., 15, p. 181, 1947. 



16. M. E. Fine and X. T. Kenny, paper to be published. 



17. H. P. J. Wijn and H. van der Heide, Revs. Mod. Phys., 25, p. 99, 1953. H. P. J. 



Wijn, Thesis, Leiden, 1953. Separaat 2092, N. V. Philips Gloeilampenfabrie- 

 ken, Eindhoven, Holland. 



18. The author wishes to acknowledge a conversation with B. T. ^Matthias in 



which this mechanism was independently suggested in connection with the 

 present research. 



19. J. L. Snoek, New Developments in Ferromagnetic Materials, Ellsevier, 1947. 



20. It should be mentioned that Xeel (J. Phys. et Radium 12, p. .3.39, 1951; 13, p. 



249, 1952) has suggested that the after-effect losses discussed by Snoek'^ in 

 connection with the diffusion of carbon and oxygen in iron arise from an 

 anisotropy relaxation. Xeel's analysis, however, leads him to jjredict zero 

 loss for large motions of a 180° domain wall, which is contrary to our ex- 

 perimental results. We suggest that he is led to an erroneous result because 

 he allows the anisotropy energy itself to follow a relaxation of the form of 

 Equation (18), whereas kinetic lo.sses of this sort are due to the relaxation 

 of one of two conjugate thermodynamical variables whose product is an 

 energy. In our case these variables are the torque on the magnetization due 

 to anisotropy, and the angle of rotation of the magnetization. It is this 

 torque which satisfies the relaxation eciuation. 



21. C. Herring and C. Kittel, Phvs. Rev., 81, p. 869, 1951. See i;<iuation o. 



22. L. R. Bickford, Jr., Phvs. Rev., 78, p. 449, 1950. 



23. C. Kittel, Phys. Rev., 76, p. 743, 1949. 



