Unification of Extant Theories of the Heisenberg Ferromagnet

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Abstract
Four recently proposed theories of the Heisenberg ferromagnet have been examined within a Green function formulation. The decoupling parameters were chosen for each theory so that the expressions for the renormalization factor and the magnetization are identical to those originally derived. Comparisons of the approximations introduced and of the results are more readily made within this single theoretical framework. The temperature dependence of the magnetization has been numerically computed for each of the four theories for simple cubic, body-centered cubic, and face-centered cubic lattices with spin ½.