Strong intrinsic room-temperature ferromagnetism in freestanding non-van der Waals ultrathin 2D crystals

AbstractControl of ferromagnetism is of critical importance for a variety of proposed spintronic and topological quantum technologies. Inducing long-range ferromagnetic order in ultrathin 2D crystals will provide more functional possibility to combine their unique electronic, optical and mechanical properties to develop new multifunctional coupled applications. Recently discovered intrinsic 2D ferromagnetic crystals such as Cr2Ge2Te6, CrI3 and Fe3GeTe2 are intrinsically ferromagnetic only below room temperature, mostly far below room temperature (Curie temperature, ~20–207 K). Here we develop a scalable method to prepare freestanding non-van der Waals ultrathin 2D crystals down to mono- and few unit cells (UC) and report unexpected strong, intrinsic, ambient-air-robust, room-temperature ferromagnetism with TC up to ~367 K in freestanding non-van der Waals 2D CrTe crystals. Freestanding 2D CrTe crystals show comparable or better ferromagnetic properties to widely-used Fe, Co, Ni and BaFe12O19, promising as new platforms for room-temperature intrinsically-ferromagnetic 2D crystals and integrated 2D devices.

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Strong room-temperature ferromagnetism in VSe2 monolayers on van der Waals substrates

Nature Nanotechnology ◽

10.1038/s41565-018-0063-9 ◽

2018 ◽

Vol 13 (4) ◽

pp. 289-293 ◽

Cited By ~ 461

Author(s):

Manuel Bonilla ◽

Sadhu Kolekar ◽

Yujing Ma ◽

Horacio Coy Diaz ◽

Vijaysankar Kalappattil ◽

...

Keyword(s):

Room Temperature ◽

Room Temperature Ferromagnetism ◽

Van Der Waals

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Room temperature ferromagnetism in ultra-thin van der Waals crystals of 1T-CrTe2

Nano Research ◽

10.1007/s12274-020-3021-4 ◽

2020 ◽

Vol 13 (12) ◽

pp. 3358-3363 ◽

Cited By ~ 4

Author(s):

Xingdan Sun ◽

Wanying Li ◽

Xiao Wang ◽

Qi Sui ◽

Tongyao Zhang ◽

...

Keyword(s):

Room Temperature ◽

Room Temperature Ferromagnetism ◽

Van Der Waals

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Nearly Room-Temperature Ferromagnetism in a Pressure-Induced Correlated Metallic State of the van der Waals Insulator CrGeTe3

Physical Review Letters ◽

10.1103/physrevlett.127.217203 ◽

2021 ◽

Vol 127 (21) ◽

Author(s):

Dilip Bhoi ◽

Jun Gouchi ◽

Naoka Hiraoka ◽

Yufeng Zhang ◽

Norio Ogita ◽

...

Keyword(s):

Room Temperature ◽

Room Temperature Ferromagnetism ◽

Van Der Waals ◽

Metallic State

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Highly‐Tunable Intrinsic Room‐Temperature Ferromagnetism in 2D van der Waals Semiconductor Cr x Ga 1− x Te

Advanced Science ◽

10.1002/advs.202103173 ◽

2021 ◽

pp. 2103173

Author(s):

Gaojie Zhang ◽

Hao Wu ◽

Liang Zhang ◽

Shanfei Zhang ◽

Li Yang ◽

...

Keyword(s):

Room Temperature ◽

Room Temperature Ferromagnetism ◽

Van Der Waals

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Above Room-Temperature Ferromagnetism in Wafer-Scale Two-Dimensional van der Waals Fe3GeTe2 Tailored by a Topological Insulator

ACS Nano ◽

10.1021/acsnano.0c03152 ◽

2020 ◽

Vol 14 (8) ◽

pp. 10045-10053 ◽

Cited By ~ 3

Author(s):

Haiyu Wang ◽

Yingjie Liu ◽

Peichen Wu ◽

Wenjie Hou ◽

Yuhao Jiang ◽

...

Keyword(s):

Topological Insulator ◽

Room Temperature ◽

Room Temperature Ferromagnetism ◽

Van Der Waals ◽

Two Dimensional ◽

Wafer Scale

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Nearly room temperature ferromagnetism in a magnetic metal-rich van der Waals metal

Science Advances ◽

10.1126/sciadv.aay8912 ◽

2020 ◽

Vol 6 (3) ◽

pp. eaay8912 ◽

Cited By ~ 9

Author(s):

Junho Seo ◽

Duck Young Kim ◽

Eun Su An ◽

Kyoo Kim ◽

Gi-Yeop Kim ◽

...

Keyword(s):

Room Temperature ◽

Room Temperature Ferromagnetism ◽

Van Der Waals ◽

Spin Current ◽

Perpendicular Magnetic Anisotropy ◽

Long Distance ◽

Effective Spin ◽

Experimental Realization ◽

Spintronic Devices ◽

Source Operation

In spintronics, two-dimensional van der Waals crystals constitute a most promising material class for long-distance spin transport or effective spin manipulation at room temperature. To realize all-vdW-material–based spintronic devices, however, vdW materials with itinerant ferromagnetism at room temperature are needed for spin current generation and thereby serve as an effective spin source. We report theoretical design and experimental realization of a iron-based vdW material, Fe4GeTe2, showing a nearly room temperature ferromagnetic order, together with a large magnetization and high conductivity. These properties are well retained even in cleaved crystals down to seven layers, with notable improvement in perpendicular magnetic anisotropy. Our findings highlight Fe4GeTe2 and its nanometer-thick crystals as a promising candidate for spin source operation at nearly room temperature and hold promise to further increase Tc in vdW ferromagnets by theory-guided material discovery.

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Magnetic critical behavior of the van der Waals Fe5GeTe2 crystal with near room temperature ferromagnetism

Scientific Reports ◽

10.1038/s41598-020-72203-3 ◽

2020 ◽

Vol 10 (1) ◽

Author(s):

Zhengxian Li ◽

Wei Xia ◽

Hao Su ◽

Zhenhai Yu ◽

Yunpeng Fu ◽

...

Keyword(s):

Critical Behavior ◽

Critical Exponents ◽

Room Temperature ◽

Room Temperature Ferromagnetism ◽

Van Der Waals ◽

Three Dimensional ◽

Magnetic Coupling ◽

Magnetic Exchange ◽

Ferromagnetic Exchange ◽

Ferromagnetic Ordering

Abstract The van der Waals ferromagnet Fe5GeTe2 has a Curie temperature TC of about 270 K, which is tunable through controlling the Fe deficiency content and can even reach above room temperature. To achieve insights into its ferromagnetic exchange that gives the high TC, the critical behavior has been investigated by measuring the magnetization in Fe5GeTe2 crystal around the ferromagnetic ordering temperature. The analysis of the measured magnetization by using various techniques harmonically reached to a set of reliable critical exponents with TC = 273.7 K, β = 0.3457 ± 0.001, γ = 1.40617 ± 0.003, and δ = 5.021 ± 0.001. By comparing these critical exponents with those predicted by various models, it seems that the magnetic properties of Fe5GeTe2 could be interpreted by a three-dimensional magnetic exchange with the exchange distance decaying as J(r) ≈ r−4.916, close to that of a three-dimensional Heisenberg model with long-range magnetic coupling.

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Tunable room-temperature ferromagnetism in Co-doped two-dimensional van der Waals ZnO

Nature Communications ◽

10.1038/s41467-021-24247-w ◽

2021 ◽

Vol 12 (1) ◽

Author(s):

Rui Chen ◽

Fuchuan Luo ◽

Yuzi Liu ◽

Yu Song ◽

Yu Dong ◽

...

Keyword(s):

Room Temperature ◽

Spontaneous Magnetization ◽

Magnetic Circular Dichroism ◽

Room Temperature Ferromagnetism ◽

Van Der Waals ◽

Single Atom ◽

Spin Interaction ◽

Two Dimensional ◽

X Ray ◽

Co Doped

AbstractThe recent discovery of ferromagnetism in two-dimensional van der Waals crystals has provoked a surge of interest in the exploration of fundamental spin interaction in reduced dimensions. However, existing material candidates have several limitations, notably lacking intrinsic room-temperature ferromagnetic order and air stability. Here, motivated by the anomalously high Curie temperature observed in bulk diluted magnetic oxides, we demonstrate room-temperature ferromagnetism in Co-doped graphene-like Zinc Oxide, a chemically stable layered material in air, down to single atom thickness. Through the magneto-optic Kerr effect, superconducting quantum interference device and X-ray magnetic circular dichroism measurements, we observe clear evidences of spontaneous magnetization in such exotic material systems at room temperature and above. Transmission electron microscopy and atomic force microscopy results explicitly exclude the existence of metallic Co or cobalt oxides clusters. X-ray characterizations reveal that the substitutional Co atoms form Co2+ states in the graphitic lattice of ZnO. By varying the Co doping level, we observe transitions between paramagnetic, ferromagnetic and less ordered phases due to the interplay between impurity-band-exchange and super-exchange interactions. Our discovery opens another path to 2D ferromagnetism at room temperature with the advantage of exceptional tunability and robustness.

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