1. L. Berger, J. Phys. Chem. Solids 35, 947 (1974).JPCSAW0022-3697
2. L. Berger, J. Appl. Phys. 49, 2156 (1978).JAPIAU0021-8979
3. V. R. V. Ramanan and L. Berger, Inst. Phys. Conf. Ser. (London) No. 39, 182 (1978).
4. V. R. V. Ramanan and L. Berger, to be published.
5. C. Kooy and U. Enz, Philips Res. Repts. 15, 7 (1960).