We investigate the thermodynamic behavior of antiferromagnetic films in external magnetic fields oriented perpendicular to the staggered magnetization. Within the systematic effective Lagrangian framework we first calculate the two-point function and the dispersion relation for the two types of magnons up to one-loop order. This allows us to split the two-loop free energy density into a piece that originates from noninteracting dressed magnons, and a second piece that corresponds to the genuine magnon–magnon interaction. We then discuss the low-temperature series for various thermodynamic quantities, including the parallel staggered and uniform perpendicular susceptibilities, and analyze the role of the spin–wave interaction at finite temperature.

我们研究了反铁磁薄膜在垂直于交错磁化方向的外部磁场中的热力学行为。在系统有效的拉格朗日框架内，我们首先计算两类磁振子的两点函数和色散关系，直至一环阶。这使我们能够将两环自由能密度分成一个非相互作用的修整磁振子，另一个对应于真正的磁振子-磁振子相互作用。然后，我们讨论了各种热力学量的低温序列，包括平行交错和均匀的垂直磁化率，并分析了自旋波相互作用在有限温度下的作用。