The spherical model of Be
The spherical model of Berlin and Kac can be used to show that this quantity varies linearly with defect concentration. Landau-Ginzburg theory defines four critical exponents related to this quantity, two of which are the degree of the critical isotherm and the heat capacity. One way of deriving this quantity is through a theory in which the effective field is replaced by its mean equilibrium value; that method produces disagreements with experiment of up to a factor of two, and is known as the Weiss theory. When this quantity is approached from below, the magnetization goes continuously to zero, and rotation symmetry is broken at this point, which represents a second-order phase transition. Above this analogue of the Neel point, magnetic ordering is lost. For 10 points, identify this temperature above which a ferromagnet becomes paramagnetic.
The spherical model of Berlin and Kac can be used to show that this quantity varies linearly with defect concentration.
Curie temperature [or Curie point]