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A generalized spherical version of the Blume-Emery-Griffits model with ferromagnetic and antiferromagnetic interactions

S. E. Savel'ev·Guillermo Ramirez-Santiago
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Abstract

We have investigated analitycally the phase diagram of a generalized spherical version of the Blume-Emery-Griffiths model that includes ferromagnetic or antiferromagnetic spin interactions as well as quadrupole interactions in zero and nonzero magnetic field. We show that in three dimensions and zero magnetic field a regular paramagnetic-ferromagnetic (PM-FM) or a paramagnetic-antiferromagnetic (PM-AFM) phase transition occurs whenever the magnetic spin interactions dominate over the quadrupole interactions. However, when spin and quadrupole interactions are important, there appears a reentrant FM-PM or AFM-PM phase transition at low temperatures, in addition to the regular PM-FM or PM-AFM phase transitions. On the other hand, in a nonzero homogeneous external magnetic field $H$, we find no evidence of a transition to the state with spontaneous magnetization for FM interactions in three dimensions. Nonethelesss, for AFM interactions we do get a scenario similar to that described above for zero external magnetic field, except that the critical temperatures are now functions of $H$. We also find two critical field values, $H_{c1}$, at which the reentrance phenomenon dissapears and $H_{c2}$ ($H_{c1}\approx 0.5H_{c2}$), above which the PM-AFM transition temperature vanishes.

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S. E. Savel'ev, Guillermo Ramirez-Santiago. 2000-11-03. A generalized spherical version of the Blume-Emery-Griffits model with ferromagnetic and antiferromagnetic interactions. https://doi.org/10.1103/physrevb.63.054424

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