AN INTERPOLATION APPROACH TO THE GREEN FUNCTION THEORY OF FERROMAGNETISM,
PENNSYLVANIA UNIV PHILADELPHIA
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The difficult problem of decoupling the Green functions of a Heisenberg ferromagnet is approached from an ad hoc point of view. The Green functions pertaining to spin problems do not obey a simple Dyson equation the higher order Green function is proportional to the lower order Green function the proportionality factor being the mass operator plus an anomalous additive term. The form of both the mass operator and the anomalous term is here evaluated by re quiring agreement of the theory with rigorous results known from low temperature and high temperature expansions. At low temperatures, the anomalous term makes a particularly signifi cant correction to the results for spin 12, but becomes relatively unimportant for higher spins. Near the Curie temperature, however, the con tribution of the anomalous term is important even for larger spin values. The resultant theory agrees with previous Curie- temperature estimates to within about one percent.
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