Hwang Inho, Coak Matthew J, Lee Nahyun, Ko Dong-Su, Oh Youngtek, Jeon Insu, Son Suhan, Zhang Kaixuan, Kim Junghyun, Park Je-Geun
Department of Physics and Astronomy, Seoul National University, Seoul 08826, Republic of Korea. Center for Correlated Electron System, Institute for Basic Science (IBS), Seoul 08826, Republic of Korea.
J Phys Condens Matter. 2019 Dec 18;31(50):50LT01. doi: 10.1088/1361-648X/ab3135.
The widely-studied ferromagnetic van-der-Waals (vdW) metal FeGeTe has great promise for studies of quantum criticality in the 2D limit, but is limited by a relatively high Curie temperature in excess of 200 K. To help render the quantum critical point achievable in such a system within the reach of practically possible tuning methods, we have grown single crystals of a variant of (Fe,Co)GeTe with useful physical properties for both this purpose and the wider study of low-dimensional magnetism and spin transport. (Fe,Co)GeTe is found through x-ray diffraction and electron microscopy to have an equivalent crystal structure to FeGeTe, with a random distribution of the cobalt dopant sites. It exhibits a sharp ferromagnetic transition at a value below 40 K, a stronger anisotropy and a coercive field ten times larger than that of FeGeTe. The transport properties and specific heat show the electronic properties and strong correlations of FeGeTe to be near-unchanged in this doped material. We demonstrate that (Fe,Co)GeTe can be cleanly exfoliated down to monolayer thickness. This unprecedented hard metallic vdW ferromagnet is a valuable new addition to the limited range of materials available for the study of 2D magnetism.
被广泛研究的铁磁范德华（vdW）金属FeGeTe在二维极限下的量子临界性研究方面极具潜力，但受限于其超过200 K的相对较高居里温度。为了使这样一个系统中的量子临界点能够通过实际可行的调谐方法实现，我们生长了一种（Fe,Co）GeTe变体的单晶，它具有对实现此目的以及更广泛的低维磁性和自旋输运研究有用的物理性质。通过X射线衍射和电子显微镜发现，（Fe,Co）GeTe具有与FeGeTe等效的晶体结构，钴掺杂位点呈随机分布。它在低于40 K时表现出尖锐的铁磁转变、更强的各向异性以及比FeGeTe大十倍的矫顽场。输运性质和比热表明，在这种掺杂材料中，FeGeTe的电子性质和强关联几乎没有变化。我们证明（Fe,Co）GeTe可以被干净地剥离到单层厚度。这种前所未有的硬金属vdW铁磁体是二维磁性研究可用材料有限范围内有价值的新成员。
