The phase transitions and thermodynamics of the antiferromagnetic system with the presence of the next-to-nearest-neighbor interaction on the body-centered cubic lattice are studied within an exactly solvable model using the recursive lattice approach. It is shown that, besides the Néel and collinear antiferromagnetic phases and the paramagnetic phase discussed in the literature, the model clearly exhibits the existence of an intermediate phase that separates the antiferromagnetic phases. This new phase is observed in a narrow interval of the frustration parameter for nonzero temperatures and is realized in the form of a discrete (single-point-like) ground state in the zero-temperature limit. Transitions between all model phases are studied and it is shown that all transitions between each antiferromagnetic phase of the model and the paramagnetic one as well as between the antiferromagnetic phases and the intermediate phase have the second-order phase transition nature. The magnetization, entropy, and specific heat capacity properties of all phases of the model are studied in detail. Three different ground states are identified and their macroscopic degeneracies are determined. The anomalous Schottky-type behavior of the specific heat capacity in the vicinity of the highly macroscopically degenerated ground state realized for exactly given value of the frustration parameter is observed and discussed. Besides, the existence of the intermediate phase leads to the nontrivial temperature behavior of the specific heat capacity where, in addition to the Schottky-type anomaly related to the frustration, three discontinuous jumps related to the three consecutive second-order phase transitions between corresponding model phases are observed.

中文翻译：

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预测以体心立方晶格的反铁磁J1-J2spin-12系统中自旋液体状相的存在

在一个精确可解的模型中，使用递归晶格方法研究了反铁磁系统在体心立方晶格上存在最近邻相互作用时的相变和热力学。结果表明，除了文献中讨论的Néel和共线反铁磁性相和顺磁性相之外，该模型还清楚地表明存在分离反铁磁性相的中间相的存在。对于非零温度，该新阶段在受挫参数的狭窄间隔中观察到，并且以零温度极限中的离散（单点状）基态形式实现。研究了所有模型相之间的跃迁，结果表明，模型的每个反铁磁相与顺磁性相之间以及反铁磁相与中间相之间的所有跃迁均具有二阶相变性质。详细研究了模型各相的磁化，熵和比热容特性。确定了三种不同的基态，并确定了它们的宏观简并性。观察并讨论了在完全给定的挫折参数值的情况下，在高度宏观退化的基态附近实现的比热的异常肖特基型行为。此外，中间相的存在导致比热容具有非平凡的温度行为，其中，