SPONTANEOUS MAGNETIZATION IN IDEALIZED FERROMAGNETS.
Technical rept. no. 19,
CALIFORNIA UNIV SAN DIEGO LA JOLLA
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An attempt, not entirely successful, is made to clarify the relation between two definitions of spontaneous magnetization in a Heisenberg or Ising ferromagnet with short range interaction. One definition uses the average magnetization in the presence of an external magnetic field, the other the probability distribution of the magnetization in the absence of a field. In connection with the latter, the analog for magnetic systems of the monotone pressure-volume relation in a gas computed in the canonical ensemble is demonstrated. The analysis requires that the total z component of magnetization commute with the Hamiltonian. Author