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arXiv 2202.05445cond-mat.str-elcond-mat.mtrl-sci
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范德华金属铁磁体Fe $_{2.72}$ GeTe $_{2}$中磁激发双重性质的中子能谱证据

Neutron spectroscopy evidence on the dual nature of magnetic excitations in a van der Waals metallic ferromagnet Fe$_{2.72}$GeTe$_{2}$

Song Bao, Wei Wang, Yanyan Shangguan, Zhengwei Cai, Zhao-Yang Dong, Zhentao Huang, Wenda Si, Zhen Ma, Ryoichi Kajimoto, Kazuhiko Ikeuchi, Shin-ichiro Yano, Shun… 展开作者

Song Bao, Wei Wang, Yanyan Shangguan, Zhengwei Cai, Zhao-Yang Dong, Zhentao Huang, Wenda Si, Zhen Ma, Ryoichi Kajimoto, Kazuhiko Ikeuchi, Shin-ichiro Yano, Shun-Li Yu, Xiangang Wan, Jian-Xin Li, Jinsheng Wen

备注：
Main text 15 pages, 5 figures. Supplementary Materials available on PRX
发表信息：
Phys. Rev. X 12, 011022 (2022)
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摘要：

在局部或巡回极端，磁激发可以用海森堡模型来描述，该模型将电子自旋视为局部矩，或者用巡回电子模型来描述，其中电子之间的交换相互作用导致具有上下自旋的电子数量不等。然而，当局域矩和巡回电子都存在于中间范围时，它一直是难以捉摸的。使用非弹性中子散射，我们提供了直接的光谱证据的共存和相互作用的局部时刻和巡回电子之间的范德华金属铁磁体Fe $_{2.72}$ GeTe $_{2}$，它可以维持可调的室温铁磁性下降到单层极限。我们发现，存在铁磁自旋波激发分散从区域中心在低能量导致的本地时刻，和一个柱状宽连续区在高能量高达100 meV以上的巡回电子导致的区域边界。与二维晶体结构不同，低能模式表现出三维性质，而高能模式也具有面外依赖性。这两种模式在居里温度160 K以上都能很好地保持。我们的中子光谱数据表明，在100 K的低能自旋波比在4 K的相干，这是近藤屏蔽在高温下减弱的证据。这些结果清楚地表明了Fe $_{2.72}$ GeTe $_{2}$中局域磁矩和巡游电子的共存以及这两种成分之间的近藤效应。这种行为通常在具有重$f$电子的重费米子系统中被预期，但在具有轻$d$电子的材料中很少清楚地观察到。这些发现有助于理解过渡金属化合物的磁性。

英文摘要：

In the local or itinerant extreme, magnetic excitations can be described by the Heisenberg model which treats electron spins as localized moments, or by the itinerant-electron model where the exchange interaction between electrons leads to unequal numbers of electrons with up and down spins. However, it has been elusive when both local moments and itinerant electrons are present in the intermediate range. Using inelastic neutron scattering, we provide direct spectroscopic evidence on the coexistence of and interplay between local moments and itinerant electrons in a van der Waals metallic ferromagnet Fe$_{2.72}$GeTe$_{2}$, which can sustain tunable room-temperature ferromagnetism down to the monolayer limit. We find that there exist ferromagnetic spin-wave excitations dispersing from the zone center at low energies resulting from local moments, and a column-like broad continuum at the zone boundary at high energies up to over 100 meV resulting from itinerant electrons. Unlike the two-dimensional crystal structure, the low-energy mode exhibits a three-dimensional nature, and the high-energy mode also has an out-of-plane dependence. Both modes persist well above the Curie temperature of 160 K. Our neutron spectroscopic data reveal that the low-energy spin waves at 100 K are more coherent than those at 4 K, which is evidence of the weakening of the Kondo screening at high temperatures. These results unambiguously demonstrate the coexistence of local moments and itinerant electrons, and the Kondo effect between these two components in Fe$_{2.72}$GeTe$_{2}$. Such behaviors are generally expected in heavy-fermion systems with heavy $f$ electrons but rarely clearly observed in materials with light $d$ electrons. These findings shed light on the understanding of magnetism in transition-metal compounds.

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