Gd-$i$-MAX电子激发中的磁有序与磁弹性
Magnetic Order and Magneto-Elasticity in the Electronic Excitations of Gd-$i$-MAX
AI总结：
本研究通过低温拉曼光谱研究Gd-$i$-MAX在26 K反铁磁相变附近的电子与声子响应，发现磁隙打开、声子硬化及弱自旋-声子耦合。
摘要：
我们报告了利用单晶样品对稀土基磁体（Mo$_{2/3}$RE$_{1/3}$）$_2$AlC（也称为RE-$i$-MAX相，其中RE=Gd、Yb和Dy）中电子集体模式的研究。文中详细研究了低温下Gd-$i$-MAX样品的拉曼光谱，重点关注与26 K反铁磁（AFM）相变相关的声子行为。在25 K以下观察到若干低频声子模式的中心频率显著移动，这与Néel转变相关。积分拉曼强度测量表明，在AFM转变温度以下电子背景降低，表明磁隙打开。我们的分析显示没有新的声子模式。因此，在我们的测量中没有看到声子模式向$Γ$点发生布里渊区折叠的任何迹象。然而，所有声子模式在低温下的硬化表明存在强自旋-声子耦合效应。利用声子频率的温度相关模型，我们确定所有频率的自旋-声子耦合常数$λ$均小于0.1 cm$^{-1}$，这与其他反铁磁材料（如$T_N$分别为68 K和78 K的MnF$_2$和FeF$_2$）中发现的数值处于同一数量级，但显著低于$T_N$为213 K的CuO。
英文摘要：
We report the investigation of electronic collective modes in rare-earth-based magnets (Mo$_{2/3}$RE$_{1/3}$)$_2$AlC (also known as RE-$i$-MAX phases), where RE=Gd, Yb, and Dy, using single crystal samples. A detailed investigation of the Raman spectra of Gd-$i$-MAX samples at low temperatures, with a focus on the phonon behavior in relation to the antiferromagnetic (AFM) phase transition at 26 K is presented. Significant shifts in the central frequencies of several low-frequency phonon modes were observed below 25 K, correlating with the Néel transition. Integrated Raman intensity measurements indicated a reduction in the electronic background below the AFM transition temperature, suggesting the opening of a magnetic gap. Our analysis showed no new phonon modes. Therefore, we do not see any indication of a Brillouin zone folding of phonon mode to the $Γ$-point in our measurement. However, the hardening of all phonon modes at low temperatures points to a strong spin-phonon coupling effect. Using a temperature-dependent model of phonon frequency, we determined the spin-phonon coupling constant $λ$ to be less than 0.1 cm$^{-1}$ for all frequencies, which is of the same order of magnitude as found in other antiferromagnetic materials such as MnF$_{2}$ and FeF$_{2}$ with $T_N=68~K$ and $T_N=78~K$, respectively, but significantly lower than that of $CuO$ with $T_N=213~K$.
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