单晶准二维蜂窝磁体YbI$_3$中的非典型反铁磁有序
Atypical antiferromagnetic ordering in single crystalline quasi-2D honeycomb magnet YbI$_3$
AI总结：
本文通过单晶生长与多种表征手段研究准二维蜂窝磁体YbI$_3$，发现其在0.6 K发生长程反铁磁有序，且低温热容指数α≈2.5，提示可能存在非常规磁基态。
摘要：
本文研究了YbI$_3$，一种准二维层状材料，其中Yb原子排列在由共边YbI$_6$八面体构成的理想蜂窝网络上，类似于$α-$RuCl$_3$的低温相。以Yb和I为起始前驱体，采用气相输运技术生长出高质量的YbI$_3$单晶。利用单晶X射线衍射、拉曼光谱、磁化强度和热容测量对所生长的晶体进行了表征。YbI$_3$中Yb$^{3+}$的晶体场劈裂基态是一个良好隔离的Kramers双重态，有效矩为$\rm J_{eff} = 1/2$。冷却时，YbI$_3$的低温热容在$\rm T_1 = 0.95$ K处出现一个宽峰，源于Yb磁矩的短程有序，随后在$\rm T_2 = T_N = 0.6$ K处出现一个尖锐峰，源于长程有序。磁性行为呈弱各向异性，$χ^\parallel > χ^\perp$，其中$χ^\parallel$和$χ^\perp$分别指面内（$H \parallel ab$）和面外（$H \perp ab$）磁化率。2 K等温磁化强度在面内饱和于$\rm \approx 1.5 μ_B/Yb^{3+}$，在面外饱和于$\rm \approx 1 μ_B/Yb^{3+}$，表明各向异性为易面型。远低于T$_N$的低温热容按T$^α$变化，$α \approx 2.5$，表明YbI$_3$可能具有非常规磁基态。
英文摘要：
Here, we study YbI$_3$, a quasi-2D layered material with Yb atoms arranged on an ideal honeycomb network of edge-sharing YbI$_6$ octahedra, analogous to the low-temperature phase of $α-$RuCl$_3$. High quality single crystals of YbI$_3$ are grown from Yb and I as starting precursors, using the vapor transport technique. The grown crystals are characterized by single crystal x-ray diffraction, Raman spectroscopy, magnetization, and heat capacity probes. The crystal-field split ground state of Yb$^{3+}$ in \Yb~ is a well-isolated Kramers doublet with an effective moment $\rm J_{eff} = 1/2$. Upon cooling, the low-temperature heat capacity of \Yb~ reveals a broad peak at $\rm T_1 = 0.95$~K due to short-range ordering of the Yb moments, followed by a sharp peak at $\rm T_2 = T_N = 0.6$~K due to long-range ordering. The magnetic behavior is found to be weakly anisotropic with $χ^\parallel > χ^\perp$, where $χ^\parallel$ and $χ^\perp$ refers to the in-plane ($H \parallel ab$) and out-of-plane ($H \perp ab$) susceptibilities. The 2~K isothermal magnetization saturates at $\rm \approx~1.5~μ_B/Yb^{3+}$ (in-plane) and $\rm \approx~1~μ_B/Yb^{3+}$ (out-of-plane), suggesting the anisotropy to be easy-plane type. Low-temperature heat capacity, well below T$_N$, is found to vary as T$^α$ with $α~\approx~2.5$, indicating a possible unconventional magnetic ground state for YbI$_3$.
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