Jahn-Teller活性氟钙钛矿$A\mathrm{CrF_3}$ $A=\mathrm{Na^+},\mathrm{K^+}$：作为$A$ -位函数的热-和磁-光关联
The Jahn-Teller active fluoroperovskites $A\mathrm{CrF_3}$ $A=\mathrm{Na^+},\mathrm{K^+}$: thermo- and magneto optical correlations as function of the $A$-site
摘要：
铬（II）氟钙钛矿$A\mathrm{CrF_3}(A\mathrm{=Na^+,K^+})$在低温下是强相关的Jahn-Teller活性材料。在本文中，我们研究的作用，$A$ -网站离子在这个家庭的氟钙钛矿使用实验方法（XRD，光吸收光谱和磁场）和DFT模拟。温度依赖的光吸收实验表明，只有在2K时，$A$ = Na的自旋允许跃迁$E_2$和$E_3$才能完全合并.在2 K下的光吸收测量结果表明，$\mathrm{NaCrF_3}$中自旋允许跃迁的振荡强度随外加电场的增加而增加.在低于Neél温度的${\rm KCrF_3}$中观察到抑制自旋翻转跃迁的直接磁结构相关性。在${\rm NaCrF_3}$中，自旋翻转跃迁在低于9 K时突然消失，揭示了与晶体结构变化无关的磁光相关性。这表明，随着长程有序性的降低，单个${\rm CrF_6^{4-}}$八面体中的局部JT效应控制了所观察到的行为。我们的结果表明，从模式发现的等电子$A_x{\rm MnF}_{3+x}$系统的明显偏差。的$A$ -网站阳离子的大小被证明是中央在支配的物理性质和相变在$A{\rm CrF}_3$，开辟了可能性的变化的组合物，以创建新的物质状态与可调性能。
英文摘要：
Chromium (II) fluoroperovskites $A\mathrm{CrF_3}(A\mathrm{=Na^+,K^+})$ are strongly correlated Jahn-Teller active materials at low temperatures. In this paper, we examine the role that the $A$-site ion plays in this family of fluoroperovskites using both experimental methods (XRD, optical absorption spectroscopy and magnetic fields) and DFT simulations. Temperature-dependent optical absorption experiments show that the spin-allowed transitions $E_2$ and $E_3$ only merge completely for $A$= Na at 2 K. Field-dependent optical absorption measurements at 2 K show that the oscillating strength of the spin-allowed transitions in $\mathrm{NaCrF_3}$ increases with increasing applied field. Direct magneto-structural correlations which suppress the spin-flip transitions are observed for ${\rm KCrF_3}$ below its Neél temperature. In ${\rm NaCrF_3}$ the spin-flip transitions vanish abruptly below 9 K revealing magneto-optical correlations not linked to crystal structure changes. This suggests that as the long range ordering is reduced local JT effects in the individual ${\rm CrF_6^{4-}}$ octahedra take control of the observed behavior. Our results show clear deviation from the pattern found for the isoelectronic $A_x{\rm MnF}_{3+x}$ system. The size of the $A$-site cation is shown to be central in dictating the physical properties and phase transitions in $A{\rm CrF}_3$, opening up the possibility of varying the composition to create novel states of matter with tuneable properties.
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