Magnetic spectral response and lattice properties in mixed-valence Sm1-xYxS solid solutions studied with X-ray diffraction, X-ray absorption spectroscopy, and inelastic neutron scattering
Magnetic spectral response and lattice properties in mixed-valence Sm1-xYxS solid solutions studied with X-ray diffraction, X-ray absorption spectroscopy, and inelastic neutron scattering
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DOI：
10.1103/physrevb.74.035114
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发表时间：
2006-07-01
影响因子：
3.7
通讯作者：
Sadikov, I. P.
中科院分区：
文献类型：
--
作者：
Alekseev, P. A.;Mignot, J. -M.;Sadikov, I. P.
用X射线衍射、X射线吸收谱和中子非弹性散射研究了Sm_（1-x）Y_xS的“黑”（B）和“金”（G）相的混合价现象。晶格常数和声子色散的结果证实，价不稳定性已经发生在B相。另一方面，在热膨胀α（T）中以及在Sm均方位移中的显著温度异常表示对于组分x=0.33和0.45的B-G转变的开始。有人认为，这些异常主要表示的电子-声子耦合的效果。在粉末和单晶上测量的磁谱响应主要由接近36 meV的Sm 2+自旋轨道分量决定。一个强烈的过阻尼Sm 3+的贡献出现只有当x >= 0.33接近室温。的准弹性信号被强烈抑制低于70 K，反映了单重混合价基态的形成。非常值得注意的是，从单晶光谱中发现，36 meV左右的信号来自两个不同的、色散的、相互作用的分支。较低的峰，证实存在从x=0.17至x=0.33至少，是暂时归因于特定的混合价态制度的激发，让人想起的“激子”峰SmB 6以前报道。
Mixed-valence phenomena occurring in the "black" (B) and "gold" (G) phases of Sm1-xYxS have been studied by x-ray diffraction, x-ray absorption spectroscopy, and inelastic neutron scattering. Lattice-constant and phonon-dispersion results confirm that the valence instability occurs already inside the B phase. On the other hand, pronounced temperature anomalies in the thermal expansion alpha(T), as well as in the Sm mean-square displacements, denote the onset of the B-G transition for the compositions x=0.33 and 0.45. It is argued that these anomalies primarily denote an effect of electron-phonon coupling. The magnetic spectral response, measured on both powder and single crystals, is dominated by the Sm2+ spin-orbit component close to 36 meV. A strongly overdamped Sm3+ contribution appears only for x >= 0.33 near room temperature. The quasielastic signal is strongly suppressed below 70 K, reflecting the formation of the singlet mixed-valence ground state. Quite remarkably, the signal around 36 meV is found, from the single-crystal spectra, to arise from two distinct, dispersive, interacting branches. The lower peak, confirmed to exist from x=0.17 to x=0.33 at least, is tentatively ascribed to an excitation specific to the mixed-valence regime, reminiscent of the "exciton" peak reported previously for SmB6.