ABSTRACT

The multiferroic properties of NaCu${}_2$O${}_2$ (NCO) around the phase transition temperature $T_N$ are studied theoretically. The total polarization P is zero without magnetic field h due to the antiferroelectric state induced by the alternate stacking of CuO${}_2$ layer with opposite spin vector chirality. Applying h P increases, goes through a maximum and vanishes at $T_N$. The magnetic field dependence of $P(h)$ is an evidence that NCO is multiferroic. For h = 0 there is no anomaly in the dielectric constant ${ϵ}^{\prime }$ at $T_N$ which is an evidence for the antiferroelectric behavior of the compound. It is observed that $P(h)$ and ${ϵ}^{\prime }(h)$ in NCO is quite different compared to that of LiCu${}_2$O${}_2$. Around the Neel temperature $T_N$ we observe in NCO an anomaly in the specific heat and the phonon energy due to strong anharmonic spin-phonon interaction. This kink disappears by applying an external magnetic field h.

摘要

NaCu的多铁性${}_2$哦${}_2$ (NCO) 相变温度附近 ${吨}_N$进行了理论研究。由于由 CuO 交替堆叠引起的反铁电态，在没有磁场h 的情况下，总极化P为零${}_2$具有相反自旋矢量手性的层。应用h P增加，经过最大值并在${吨}_N$. 的磁场依赖性$磷(H)$是 NCO 是多铁性的证据。对于h = 0，介电常数没有异常${\epsilon }^{\prime }$ 在 ${吨}_N$这是化合物反铁电行为的证据。据观察，$磷(H)$ 和 ${\epsilon }^{\prime }(H)$ 在 NCO 中与 LiCu 相比有很大不同${}_2$哦${}_2$. 尼尔温度${吨}_N$由于强非谐自旋-声子相互作用，我们在 NCO 中观察到比热和声子能量的异常。这种扭结通过施加外部磁场h消失。