潜在多铁性Aurivillius相Bi $_5$ FeTi PDMATHAAC O $_{15}$：第一性原理的阳离子位置偏好、电极化的强度和磁耦合
The potentially multiferroic Aurivillius phase Bi$_5$FeTi$_3$O$_{15}$: cation site preference, electric polarization, and magnetic coupling from first principles
摘要：
利用第一性原理电子结构计算方法研究了具有潜在多铁性的Aurivillius相材料Bi $_5$ FeTi $_3$ O $_{15}$的结构、铁电和磁性.计算进行PBE和PBESol交换相关泛函。我们的结论是PBE系统高估的晶格常数和铁电畸变的幅度，而PBESol导致良好的协议与现有的实验数据。然后，我们通过比较钙钛矿$B$-位点的10种不同分布来评估Fe $^{3+}$阳离子的潜在位点偏好。我们发现一个轻微的偏好的“内部”网站，与最近的实验观察。我们得到了一个大的值$\sim$ 55 $μ$ C/cm $^2$的自发电极化的强度，这是相当独立的特定的Fe分布。最后，我们计算了磁耦合常数的强度，发现Fe $^{3+}$阳离子之间的强反铁磁耦合在最近的邻居的位置，而更远的邻居之间的耦合是相当弱的。这就提出了一个问题，即尽管磁性离子的浓度很低，但在这个系统中是否会发生磁性长程有序。
英文摘要：
We study the structural, ferroelectric, and magnetic properties of the potentially multiferroic Aurivillius phase material Bi$_5$FeTi$_3$O$_{15}$ using first principles electronic structure calculations. Calculations are performed both with PBE and PBEsol exchange correlation functionals. We conclude that PBE systematically overestimates the lattice constants and the magnitude of the ferroelectric distortion, whereas PBEsol leads to good agreement with available experimental data. We then assess a potential site preference of the Fe$^{3+}$ cation by comparing 10 different distributions of the perovskite $B$-sites. We find a slight preference for the "inner" site, consistent with recent experimental observations. We obtain a large value of $\sim$55 $μ$C/cm$^2$ for the spontaneous electric polarization, which is rather independent of the specific Fe distribution. Finally, we calculate the strength of the magnetic coupling constants and find strong antiferromagnetic coupling between Fe$^{3+}$ cations in nearest neighbor positions, whereas the coupling between further neighbors is rather weak. This poses the question whether magnetic long range order can occur in this system in spite of the low concentration of magnetic ions.
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