Giant spin-induced ferroelectric polarization has been observed in the multiferroic $\mathrm{CaM}{\mathrm{n}}_7{\mathrm{O}}_{12}$, the origin of which remains controversial. Various theoretical models have been proposed in this regard, some of which put the preformed orbital order as a prerequisite factor, while others attribute it to the combination of Dzyaloshinskii-Moriya interactions and exchange striction. In this paper, we resolve this issue by replacing Ca with disordered $\mathrm{B}{\mathrm{i}}^{3+}/\mathrm{A}{\mathrm{g}}^{+}$ ions through high-pressure and high-temperature methods, leading to the successful synthesis of single-phase isostructural $\left(\mathrm{B}{\mathrm{i}}_{0.5}\mathrm{A}{\mathrm{g}}_{0.5}\right)\mathrm{M}{\mathrm{n}}_7{\mathrm{O}}_{12}$. No orbital order is observed down to 30 K, while a giant electric polarization of $\sim 1900\mu \mathrm{C}{\mathrm{m}}^{-2}$ is realized below $T_{\mathrm{N}}\approx 80$ K when the system enters an antiferromagnetically ordered state. The low-temperature spin structure adopts the magnetic point group of ${31}^{\prime }$, the same as $\mathrm{CaM}{\mathrm{n}}_7{\mathrm{O}}_{12}$. Our results strongly indicate that the giant ferroelectric polarization is primarily caused by exchange striction instead of orbital order.

中文翻译：

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(Bi0.5Ag0.5)Mn7O12 中无轨道有序的情况下的巨大自旋诱导电极化

在多铁性中观察到巨大的自旋诱导铁电极化$\mathrm{钙调蛋白}{\mathrm{n}}_7{\mathrm{氧}}_{12}$，其起源仍有争议。在这方面人们提出了各种理论模型，其中一些将预先形成的轨道顺序作为先决条件，而另一些则将其归因于 Dzyaloshinskii-Moriya 相互作用和交换严格的结合。在本文中，我们通过用无序取代 Ca 来解决这个问题$\mathrm{乙}{\mathrm{我}}^{3+}/\mathrm{A}{\mathrm{G}}^{+}$通过高压高温的方法，成功合成了单相同构结构的离子$（\mathrm{乙}{\mathrm{我}}_{0.5}\mathrm{A}{\mathrm{G}}_{0.5}）\mathrm{中号}{\mathrm{n}}_7{\mathrm{氧}}_{12}$。低至 30 K 时未观察到轨道序，而巨大的电极化$～\mathrm{1900年}\mu \mathrm{C}{\mathrm{米}}^{-2}$下面实现了${\mathrm{时间}}_{\mathrm{氮}}\approx 80$K 当系统进入反铁磁有序状态时。低温自旋结构采用磁点群${31}^{\prime }$，与$\mathrm{钙调蛋白}{\mathrm{n}}_7{\mathrm{氧}}_{12}$。我们的结果强烈表明，巨大的铁电极化主要是由交换严格而不是轨道有序引起的。