Frequency Dependence of Elastic Constants and Losses in Nickel

2.5 X 10"4, and use of equation (2) with this and other appropriate values indicates that the domain size is / - 0.035 m m , (21) as reported above. A check on this value can be obtained from the frequency, / m , corresponding to the maximum of the 3 vs / curve. If we use equation (16), Ppfm/R - 0.13, (22) w i t h / = 1.5 X 10* (Fig. 11), we find I -- 0.045 m m , in reasonable agreement. An actual photograph of domains in a single crystal of nickel, taken by H. J. Williams and reproduced in Fig. 13, shows the presence of domains of various sizes ranging from about 0.01 to 0.2 mm. Any such range in domain sizes will naturally tend to flatten the maximum of the 6 vs / curve and, on account of the form of the 6 vs / function, will push the maximum to a higher frequency than that corresponding to the initial slope, and will give a lower maximum value to the decrement frequency curve. The average domain size derived from our experiments is somewhat larger than that previously obtained in 68 Permalloy. 6 This may be expected, for nickel has a very high magnetostriction and the movement of domain boundaries by stress will be relatively large, possibly so large that the regions swept over by the domain walls will correspond to whole domains of the original domain structure, when the stresses are equal to those used in our experiments. The domain size which we have determined is based on this interpretation. APPENDIX METHOD OF MEASUREMENT--FORMULAE From transmission line theory (see reference of footnote 12) the ratio of outputs, r, defined in the text and applicable to the circuit of Fig.