Calculation of critical indices for systems with strong dipole interaction

Abstract

In ferromagnets and ferroelectrics, dipole interaction reduces critical fluctuations and changes the critical indices. In the present paper the critical indices of susceptibility and specific heat for three-dimensional systems with dipole forces are calculated without taking account of anisotropy. This formulation of the problem has been justified over a wide temperature range for cubic ferromagnets and ferroelectrics of the displacement type where the influence of the cubic anisotropy is small in comparison with the dipole forces. Cubic anisotropy appears in a very small neighborhood of the Curie point, transforming the transition into a phase transition of the first kind [1]. Uniaxial ferromagnets with weak anisotropy also have a dipole region where the anisotropy is significant [2]. The critical indices for systems with dipole interactions in (4-ɛ)-dimensional space have been calculated in [3, 4]. The Hamiltonian of a ferromagnet (ferroelectric) without allowance for anisotropy is of the form