1. Young, D. P. et al.Nature 397, 412–414 (1999).
2. Bloch, F. Z. Phys. 57, 545–555 (1929).
3. Wigner, E. P. Phys. Rev. 46, 1002–1011 (1934).
4. Stoner, E. C. Proc. R. Soc. Lond. A 165, 372–414 (1938).
5. Herring, C. in Magnetism Vol. IV (eds Rado, G. T. & Suhl, H.) 9-31; 71-80(Academic, San Diego, 1966).