Physics of Scale Activities

1952
Spherical model of a ferromagnet
Let the spin values of the Ising ferromagnet take on continuous values, and the partition function becomes a tractable integral. Berlin and Kac constrained the sum of the squares of the spin values to be equal to the number of lattice sites, and obtained an exactly soluble three- dimensional model that exhibited a phase transition in non- zero field. The model did not approximate any known physical systems, but it did later prove useful as a first step in Wilson's application of the renormalization group.

Primary: T. H. Berlin and M. Kac, "The spherical model of a ferromagnet," Phys. Rev. 86 (1952): 821-835.

Secondary: Domb 1996, 179. Hoddeson et al. 1992, 574.
--Karl Hall