第二阶段MnCl $_{2}$石墨层间化合物的Specific heat：自旋玻璃相和无公度短程自旋有序共存
Specific heat of stage-2 MnCl$_{2}$ graphite intercalation compound: co-existence of spin glass phase and incommensurate short-range spin order
摘要：
第二阶段MnCl $_{2}$ GIC的磁性行为类似于三角晶格上的准二维$XY$反铁磁体。在自旋冻结温度$T_{SG}$（= 1.1 K）以下，它表现出典型的自旋玻璃行为。在$H$ = 0时，AC磁化率在$T$ = $T_{SG}$处显示峰值。根据de Almeida-Almeidas临界线，该峰随着$H$的增加而向低温侧移动。我们已经进行了广泛的研究$T$依赖的比热在没有一个外部场$H$和在$H$的存在下沿$c$平面。磁比热$C_{mag}$在$H$ = 0时，在$T_{SG}$处没有异常，但在5 K和41 K附近出现双宽峰。在$H$ = 0时的磁比热$C_{mag}$由具有$Δ= 1.41 \pm 0.03$ K的$C_{mag} \propto (1/T^{2})\exp(-Δ/T)$描述，而在$H$ = 10 kOe时的$C_{mag}$与$T$成比例。由5 K附近的宽峰引起的熵是总熵的1/3。由于系统的高阻挫性质，剩余熵约占总熵的63%.磁中子散射表明，与无公度波矢量$| {\bf Q}_{incomm}|$（$= 0.522 Å^{-1}$在0.45 K）相关的短程自旋序出现低于5 K，并保持不变，下降到63 mK。在0.45K时，面内自旋相关长度仅为18 $Å$。低于$T_{SG}$的低温相是一种重入自旋玻璃相，其中自旋玻璃相与与$| {\bf Q}_{incomm}|$相关的短程自旋序共存。
英文摘要：
Stage-2 MnCl$_{2}$ GIC magnetically behaves like a quasi 2D $XY$ antiferromagnet on the triangular lattice. It shows a typical spin glass behavior below the spin freezing temperature $T_{SG}$ (= 1.1 K). The AC magnetic susceptibility shows a peak at $T$ = $T_{SG}$ at $H$ = 0. This peak shifts to the low temperature side with increasing $H$, according to the de Almeida-Thouless critical line. We have undertaken an extensive study on the $T$ dependence of specific heat in the absence of an external field $H$ and in the presence of $H$ along the $c$ plane. The magnetic specific heat $C_{mag}$ at $H$ = 0 shows no anomaly at $T_{SG}$, but exhibits double broad peaks around 5 K and 41 K. The magnetic specific heat $C_{mag}$ at $H$ = 0 is described by $C_{mag} \propto (1/T^{2})\exp(-Δ/T)$ with $Δ= 1.41 \pm 0.03$ K, while $C_{mag}$ at $H$ = 10 kOe is proportional to $T$. The entropy due to the broad peak around 5 K is 1/3 of the total entropy. The residual entropy is 63 % of the total entropy because of highly frustrated nature of the system. The magnetic neutron scattering indicates that a short range spin order associated with the incommensurate wave vector $| {\bf Q}_{incomm}|$ ($= 0.522 Å^{-1}$ at 0.45 K) appears below 5 K and remains unchanged down to 63 mK. The in-plane spin correlation length is only 18 $Å$ at 0.45 K. The low temperature phase below $T_{SG}$ is a kind of reentrant spin glass phase where the spin glass phase coexists with a short range spin order associated with $| {\bf Q}_{incomm}|$.
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