Field Theories of the Second-Order, Phase-Change

MEAN-FIELD THEORIES OF THE SECOND-ORDER, PHASE-CHANGE 

The second-order, phase-change exhibited by ferromagnets (Section 6), antiferromagnets (Section 7) and by superconductors (Section 8) have a phenomenological description in terms of the mean-field equation, 

By analogy to the liquid-vapor equilibrium the system is said to be condensed for 2 0. The critical temperature is expressed in terms of a Heisenberg exchange parameter 

The mean-field equation will be derived from two models the uniform interaction model and the Ising model. Neither of the two derivations depend explicitly on spin. They will be applied to the freeon theory of ferromagnetism Section 6 and freeon theory of high-Tc superconductivity in Section 7. 

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