Department of Physics, Graduate School of Science and Engineering, Saga University, Saga 840-8502, Japan.
J Phys Condens Matter. 2013 Jun 26;25(25):256003. doi: 10.1088/0953-8984/25/25/256003. Epub 2013 May 30.
Raman spectroscopy is a valuable and complementary tool for studying geometrically frustrated magnetic systems due to the intrinsic spin-phonon coupling. Here, we report on a Raman spectroscopic study of the geometrically frustrated spin 1/2 antiferromagnet microcrystalline clinoatacamite Cu2(OH)3Cl, focusing on the anomalous transition into the intermediate phase at T(c1) = 18.1 K. By measuring the temperature-dependent (295-4 K) full spectral profiles and main representative modes in spectral regions from 4000 to 95 cm(-1), we observed probable signatures of successive magnetic transitions near T(c1) = 18 K and T(c2) = 6.4 K in the Raman band frequencies and peak widths of the representative modes. Further, we observed a pronounced Raman spectroscopy background featuring a broad continuum at all temperatures. A quantitative analysis reveals that spin fluctuations may exist on a picosecond time scale in the intermediate phase. The short time scale falls out of the μSR time window; therefore, in the intermediate phase, the μSR study as reported in (2005 Phys. Rev. Lett. 95 057201) apparently only probed the local field of the ordered spins but overlooked the quickly fluctuating ones. This is likely to give a reasonable explanation of the fact that only a small entropy release occurs at T(c1) = 18 K although a long-range order is formed.
拉曼光谱学是研究几何各向异性受阻磁体系统的一种非常有价值且互补的工具，因为它具有内在的自旋-声子耦合。在此，我们报告了对几何各向异性受阻的自旋 1/2 反铁磁微晶斜氯铜矿 Cu2(OH)3Cl 的拉曼光谱研究，重点关注在 T(c1)=18.1 K 时进入中间相的异常转变。通过测量温度依赖的（295-4 K）全光谱轮廓以及在光谱区域 4000 到 95 cm(-1) 的主要代表性模式，我们在拉曼频带频率和代表性模式的峰宽附近观察到在 T(c1)=18 K 和 T(c2)=6.4 K 附近可能发生的连续磁转变的特征。此外，我们观察到在所有温度下都存在显著的拉曼光谱背景，具有一个宽的连续谱。定量分析表明，在中间相可能存在皮秒时间尺度的自旋涨落。短时间尺度超出 μSR 的时间窗口；因此，在中间相，正如（2005 Phys. Rev. Lett. 95 057201）中报道的 μSR 研究显然只探测了有序自旋的局部场，而忽略了快速波动的自旋。这很可能合理地解释了尽管形成了长程有序，但在 T(c1)=18 K 时只发生了较小的熵释放这一事实。
