Literally two‐dimensional magnets

The theoretical description of phase transitions remains a challenging problem in statistical physics. Looking for mathematically simple systems, theorists have investigated one‐ and two‐dimensional models. Such models, however present a challenge to experimenters: The world remains—except in very special cases—stubbornly three dimensional. Recent experiments, however, have produced what are apparently truly two‐dimensional magnets: manganese stearate films deposited on quartz plates and oxygen adsorbed on exfoliated graphite. Because the substrates are nonmagnetic and have completely different structures from the adsorbed substances, the magnetic ordering can only be two‐dimensional. These systems may become useful in investigations of the general properties of phase transitions as well as the specifically two‐dimensional theories (PHYSICS TODAY, August 1978, page 17, and April 1980, page 17).