Neutron Spectroscopy Evidence on the Dual Nature of Magnetic Excitations in a van der Waals Metallic Ferromagnet Fe2.72GeTe2
Neutron Spectroscopy Evidence on the Dual Nature of Magnetic Excitations in a van der Waals Metallic Ferromagnet Fe2.72GeTe2
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范德华金属铁磁体 Fe2.72GeTe2 磁激发双重性质的中子能谱证据
DOI：
10.1103/physrevx.12.011022
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发表时间：
2022
影响因子：
12.5
通讯作者：
Jinsheng Wen
中科院分区：
文献类型：
--
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
在局部或流动极端情况下，磁激发可以通过海森堡模型来描述，该模型将电子自旋视为局部力矩，或者通过流动电子模型来描述，其中电子之间的交换相互作用导致上下自旋的电子数量不等。然而，当局部力矩和流动电子都存在于中间范围时，磁激发的性质一直难以捉摸。利用非弹性中子散射，我们提供了范德华金属铁磁体中局部矩和流动电子的共存和相互作用的直接光谱证据，该铁磁体可以将可调谐的室温铁磁性维持在单层极限。我们发现，存在因局部矩而产生的低能量从区域中心分散的铁磁自旋波激发，以及因流动电子而产生的高达 100 meV 以上的高能量，在区域边界处存在柱状宽连续谱。与二维晶体结构不同，低能模式表现出三维性质，高能模式还具有面外依赖性。两种模式都持续远高于 160 K 的居里温度。我们的中子能谱数据表明，100 K 的低能自旋波比 4 K 的低能自旋波更相干，这是近藤屏蔽在高温下减弱的证据。这些结果明确地证明了局域矩和流动电子的共存以及这两个组件之间的近藤效应。这种行为通常在具有重电子的重费米子系统中出现，但在具有轻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。
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, the nature of the magnetic excitations 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, 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 columnlike 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. Such behaviors are generally expected in heavy-fermion systems with heavyelectrons but are rarely clearly observed in materials with lightelectrons. These findings shed light on the understanding of magnetism in transition-metal compounds.