NdFe $_{0.5}$ Mn $_{0.5}$ O $_{3}$的自旋重取向：中子散射和\emph{Ab-initio}研究
Spin reorientation in NdFe$_{0.5}$Mn$_{0.5}$O$_{3}$: Neutron scattering and \emph{Ab-initio} study
摘要：
采用体磁化强度、中子/X射线衍射和第一性原理密度泛函理论计算方法对NdFe $_{0.5}$ Mn $_{0.5}$ O $_3$的结构、磁性和电子性质进行了详细的研究。该材料以正交$Pbnm$结构结晶，其中Mn和Fe占据相同的晶体学位置（$4b$）。Mn/Fe亚晶格在250 K附近为G型反铁磁相，磁结构属于$Γ_{1}$不可约表示，自旋沿晶体学$b$方向排列.这是非常规的，因为大多数正铁氧体和正铬铁矿在低于Néel温度的$Γ_{4}$表示中是有序的。然后，这种磁性结构在75 °，K $\gtrsim$ T $\gtrsim$ 25 °范围内经历完全的自旋重取向转变，其中磁结构作为两个不可约表示（$Γ_{1}$ + $Γ_{2}$）的和存在，如从中子衍射测量中看到的。在6 K时，磁结构完全属于$Γ_{2}$表象，自旋沿结晶学$c$方向反铁磁排列，具有小的铁磁分量（$F_x$）.用GGA+U和GGA+U+SO形式下的第一性原理计算研究了异常的自旋重取向和磁基态与电子结构之间的相关性。
英文摘要：
The structural, magnetic, and electronic properties of NdFe$_{0.5}$Mn$_{0.5}$O$_3$ have been studied in detail using bulk magnetization, neutron/x-ray diffraction and first principles density functional theory calculations. The material crystallizes in the orthorhombic $Pbnm$ structure, where both Mn and Fe occupy the same crystallographic site ($4b$). Mn/Fe sublattice of the compound orders in to a G-type antiferromagnetic phase close to 250\,K where the magnetic structure belongs to $Γ_{1}$ irreducible representation with spins aligned along the crystallographic $b$ direction. This is unconventional in the sense that most of the orthoferrites and orthochromites order in the $Γ_{4}$ representation below the Néel temperature.This magnetic structure then undergoes a complete spin reorientation transition with temperature in the range 75\,K$\gtrsim$ T $\gtrsim$ 25\,K where the magnetic structure exists as a sum of two irreducible representations ($Γ_{1}$+$Γ_{2}$) as seen from neutron diffraction measurements. At 6\,K, the magnetic structure belongs entirely to $Γ_{2}$ representation with spins aligned antiferromagnetically along the crystallographic $c$ direction having a small ferromagnetic component ($F_x$). The unusual spin reorientation and correlation between magnetic ground state and electronic structure have been investigated using first principles calculations within GGA+U and GGA+U+SO formalisms.
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