Internal energy and magnetic moment of three-dimensional ferromagnets

Abstract

The unique relationship between the reduced internal energy and magnetic moment is investigated for a three-dimensional ferromagnet on the basis of a many-body k-space spin-wave solution of an anisotropic Heisenberg Hamiltonian of general site spin S. Spin-wave interactions up through terms quartic in Boson creation and annihilation operators are considered. The three-dimensional lattice on which the Hamiltonian is developed is in terms of the so-called "bundle representation" for three independent axes as applicable to systems of orthorhombic and higher symmetry. The Hamiltonians considered are general enough to encompass models ranging from the ordinary (isotropic) Heisenberg Hamiltonian to the anisotropic Ising Hamiltonian, all for general values of S. (C) 2003 Wiley Periodicals, Inc.