1. 1. Beno, M. A. et al. Appl. Phys. Lett, (in the press).
2. 2. Capponi, J. J. et al. Europhys. Lett. 3, 1301–1308 (1987).
3. 3. Beech, F., Miraglia, S., Santoro, A. & Roth, R. S. Phys. Rev. Lett, (in the press).
4. 4. David, W. I. F. et al. Nature 327, 310–312 (1987).
5. 5. Greedan, J. E., O'Reilly, A. & Stager, C. V. Phys. Rev. (submitted).