We investigate the Sn composition dependence of the Yb valence and local magnetization in ${\mathrm{YbMn}}_6{\mathrm{Ge}}_{6-x}{\mathrm{Sn}}_x$ ($4.25\le x\le 5.80$) using x-ray absorption spectroscopy (XANES) and x-ray magnetic circular dichroism at the Yb $L_3$ edge. In these materials, where Mn is ferromagnetically ordered, we observe a decrease of the Yb valence upon reducing the chemical pressure by Sn doping and a suppression of the Yb magnetic moment for strongly hybridized $4f$ states ($\nu \sim 2.77$). In the vicinity of the Yb magnetic instability ($x_c\sim 5.23$), a remarkably sharp peak is observed in the composition dependence of the valence and magnetic moment at low temperature, which is reminiscent of enhanced valence and magnetic susceptibilities predicted by recent theories on unconventional quantum criticality. This anomaly is also present in the room-temperature XANES signal, suggesting that rare-earth intermetallics with a magnetized $3d$ sublattice form a distinct group of heavy-fermion metals where the high energy of the exchange interactions can bring quantum criticality up to high temperature.

中文翻译：

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YbMn6Ge6-xSnx中非常规4f电子量子临界的室温特征

我们研究了锡的Yb价和局部磁化强度对Sn成分的依赖性 ${\mathrm{b锰}}_6{\mathrm{通用电器}}_{6-X}{锡}_X$ （$4.25\le X\le 5.80$）使用X射线吸收光谱（XANES）和Yb处的X射线磁性圆二色性 ${\mathrm{大号}}_3$边缘。在这些材料中，Mn是铁磁有序的，我们观察到通过掺杂Sn降低化学压力会降低Yb价，并抑制强杂交的Yb磁矩。$4F$ 状态 （$\nu 〜2.77$）。在Yb附近的磁不稳定（$X_C〜5.23$），在低温下价和磁矩的成分依赖性中观察到一个非常尖锐的峰，这使人想起了最新的非常规量子临界理论预测的价和磁化率的提高。室温XANES信号中也存在这种异常现象，表明稀土金属间化合物已被磁化$3d$ 亚晶格形成一组重金属，其中交换相互作用的高能量可以使量子临界温度升高。