We show that interlayer spins play a dual role in the Cairo pentagonal magnet ${\mathrm{Bi}}_4{\mathrm{Fe}}_5{\mathrm{O}}_{13}\mathrm{F}$, on one hand mediating the three-dimensional magnetic order, and on the other driving spin-reorientation transitions both within and between the planes. The corresponding sequence of magnetic orders unraveled by neutron diffraction and Mössbauer spectroscopy features two orthogonal magnetic structures described by opposite local vector chiralities, and an intermediate, partly disordered phase with nearly collinear spins. A similar collinear phase has been predicted theoretically to be stabilized by quantum fluctuations, but ${\mathrm{Bi}}_4{\mathrm{Fe}}_5{\mathrm{O}}_{13}\mathrm{F}$ is very far from the relevant parameter regime. While the observed in-plane reorientation cannot be explained by any standard frustration mechanism, our ab initio band-structure calculations reveal strong single-ion anisotropy of the interlayer ${\mathrm{Fe}}^{3+}$ spins that turns out to be instrumental in controlling the local vector chirality and the associated interlayer order.

中文翻译：

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开罗五角形磁体Bi4Fe5O13F中的自旋取向转变

我们证明层间自旋在开罗五角形磁铁中起双重作用 ${双}_4{铁}_5{\mathrm{Ø}}_{13}\mathrm{F}$一方面介导三维磁性，另一方面在平面内和平面之间驱动自旋重取向转变。由中子衍射和穆斯堡尔光谱解开的相应磁阶序列具有两个正交的磁性结构，分别由相反的局部矢量手性描述，中间是部分共混的自旋相，具有几乎共线的自旋。从理论上讲，类似的共线相位已被量子涨落所稳定，但${双}_4{铁}_5{\mathrm{Ø}}_{13}\mathrm{F}$与相关的参数制度相距甚远。尽管观察到的面内重新定向无法用任何标准的挫折机制来解释，但我们的从头算带结构计算显示出中间层的强单离子各向异性${铁}^{3+}$ 旋转对于控制局部矢量手性和相关的层间顺序很有帮助。