1. N D Mermin and H Wagner, Phys. Rev. Lett. 17, 1133 (1966); 17, 1307 (1966)
2. V L Berezinskii, Sov. Phys. JETP 32, 493 (1971)
3. V L Berezinskii, Sov. Phys. JETP 34, 610 (1972)
4. C M Schneider and J Kirschner, Handbook of surface science edited by K Horn and M Scheffler (Elsevier, Amsterdam, 2000), p. 511
5. P Bruno, Phys. Rev. Lett. 87, 137203 (2001)