Tricritical points in ferromagnets with cubic single-ion anisotropy

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Abstract

Certain physical systems with n⩾2 component Hamiltonians exhibit first order phase transitions, even though Landau theory predicts a continuous transition and an appropriate stable fixed point exists. Such a situation can occur if the LGW Hamiltonian parameters lie outside the domain of attraction of the stable fixed point. These parameters are calculated as functions of microscopic constants and temperature (T) for ferromagnets with single-ion cubic anisotropy (K). The phase diagram in the plane (K, T) is constructed and the domain of attraction of the isotropic n=3 stable fixed point, and then the coordinates of the tricritical points for this system are found. It is shown that in both cases, K > 0 and K < 0, such ranges of the ratio K/J exists for which the phase transition is expected to be of the first order. The usefulness of the model under consideration to the description of the transitions between phases with distinct propagation vectors are discussed.

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