1. T. Luhman and M. Suenaga, Appl. Phys. Lett.
29:61 (1976).
2. T. Luhman and M. Suenaga, IEEE Trans. Magn.
MAG-13:800 (1976).
3. H. Hillman, H. Kuckuck, H. Pfister, G. Rupp, E. Springer, M. Wilhelm, K. Wohlleken, and G. Zeigler, IEEE Trans. Magn.
MAG-13:792 (1976).
4. C. F. Old and J. P. Charlesworth, Cryogenics
16:469 (1976).
5. L. R. Testardi, in Physical Accoustics, Vol. 10 (W. P. Mason and R. N. Thurston, eds.), Academic Press, New York (1973), p. 193.