Thermal Properties of the System of Magnetic Bosons : Bose-Einstein Ferromagnetism

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Thermal and magnetic properties of the system of ideal magnetic bosons exposed to a magnetic field are investigated. The Boson particle is assumed to have a spin of magnitude one and a magnetic moment m_0. The result are summarized as follows : 1) The grand thermodynamical potential of the system has a certain singularity on the field versus temperature (T-H) plane, in which two sorts of singular lines SL_1 and SL_3 as shown in Fig. 1 appear. 2) The Bose-Einstein (BE) condensation occurs in a lower temperature and higher field region bounded by the line SL_3 or ACB on the T-H plane. 3) A spontaneous magnetization appears below a critical temperature, at which the zero field susceptibility diverges. This nature is called the "BE Ferromagnetism" in this paper. 4) The system exhibits a phase transition of first order on the line SL_1 and that of third order on SL_3. The transition reduces to the second order one at the critical temperature T_0. 5) The critical exponents at T_0 are found to be α=α=0, β=γ=1 and δ=2, which satisfy the Griffiths inequalities. In conclusion, the system of magnetic bosons which can really exist is also discussed.
理論物理学刊行会の論文
1982-02-25