text: One immediate consequence of this equation and its solution is that, if the applied field is non-zero, then the magnetization is non-zero at any temperature. This implies there is no longer a spontaneous symmetry breaking that occurs at any temperature. Furthermore, some interesting thermodynamic and universal quantities can be obtained from this above condition. For example, at the critical temperature where , one can find the dependence of the order parameter on the external field:
  indicating a critical exponent .
  Furthermore, from the above condition, it is possible to find the zero-field susceptibility , which must satisfy
  In this case, recalling in the zero-field case that  at low temperatures, while  for temperatures above the critical temperature, the zero-field susceptibility therefore has the following temperature dependence:
  which is reminiscent of the Curie-Weiss law for the temperature dependence of magnetic susceptibility in magnetic materials, and yields the mean-field critical exponent .
  It is noteworthy that although the critical exponents so obtained are incorrect for many models and systems, they correctly satisfy various exponent equalities such as the Rushbrook equality: .
  First-order transitions
  Landau theory can also be used to study first-order transitions. There are two different formulations, depending on whether or not the system is symmetric under a change in sign of the order parameter.
  I. Symmetric Case
  Here we consider the case where the system has a symmetry and the energy is invariant when the order parameter changes sign.