Fabrication and magnetic–electronic properties of van der Waals Cr <sub>4</sub>Te <sub>5</sub> ferromagnetic films

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Abstract

The layered Cr ₄Te ₅ epitaxial film was fabricated by PLD technology. It displays a PM–FM phase transition and retains a FM ordering state up to room temperature.

Abstract

Exploiting two-dimensional van der Waals (2D vdW) room temperature ferromagnetic materials is always significant and valuable work. However, the actual number of satisfactory materials with intrinsic ferromagnetism is very limited. Here, the 2D layered Cr ₄Te ₅ epitaxial films prepared by a pulsed laser deposition technique were confirmed to hold a ferromagnetic ordering state up to 300 K. We find that the Cr ₄Te ₅ films can easily achieve epitaxial growth along a single orientation of the hexagonal Al ₂O ₃(0001) substrate. However, as for the cubic SrTiO ₃(001) and multiphase structure mica substrates, the Cr ₄Te ₅ films only show uniaxial growth instead of epitaxial growth. Based on the investigation of electronic transport in the metallic regime, it is revealed that the interaction of electron–magnon scattering only exists in the lower temperature region. Our work renders 2D vdW Cr ₄Te ₅ crystals a very promising material for developing practical spintronic nanodevices.

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Most cited references 22

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2D transition metal dichalcogenides

Oleg Yazyev, Diego José Pasquier, Dmitry A. Ovchinnikov … (2017)

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Layer-dependent ferromagnetism in a van der Waals crystal down to the monolayer limit

Bevin Huang, Genevieve Clark, Efren Navarro-Moratalla … (2017)

Since the discovery of graphene, the family of two-dimensional materials has grown, displaying a broad range of electronic properties. Recent additions include semiconductors with spin–valley coupling, Ising superconductors that can be tuned into a quantum metal, possible Mott insulators with tunable charge-density waves, and topological semimetals with edge transport. However, no two-dimensional crystal with intrinsic magnetism has yet been discovered; such a crystal would be useful in many technologies from sensing to data storage. Theoretically, magnetic order is prohibited in the two-dimensional isotropic Heisenberg model at finite temperatures by the Mermin–Wagner theorem. Magnetic anisotropy removes this restriction, however, and enables, for instance, the occurrence of two-dimensional Ising ferromagnetism. Here we use magneto-optical Kerr effect microscopy to demonstrate that monolayer chromium triiodide (CrI3) is an Ising ferromagnet with out-of-plane spin orientation. Its Curie temperature of 45 kelvin is only slightly lower than that of the bulk crystal, 61 kelvin, which is consistent with a weak interlayer coupling. Moreover, our studies suggest a layer-dependent magnetic phase, highlighting thickness-dependent physical properties typical of van der Waals crystals. Remarkably, bilayer CrI3 displays suppressed magnetization with a metamagnetic effect, whereas in trilayer CrI3 the interlayer ferromagnetism observed in the bulk crystal is restored. This work creates opportunities for studying magnetism by harnessing the unusual features of atomically thin materials, such as electrical control for realizing magnetoelectronics, and van der Waals engineering to produce interface phenomena.

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Discovery of intrinsic ferromagnetism in two-dimensional van der Waals crystals

Cheng Gong, Lin Li, Zhenglu Li … (2017)

The realization of long-range ferromagnetic order in two-dimensional van der Waals crystals, combined with their rich electronic and optical properties, could lead to new magnetic, magnetoelectric and magneto-optic applications. In two-dimensional systems, the long-range magnetic order is strongly suppressed by thermal fluctuations, according to the Mermin–Wagner theorem; however, these thermal fluctuations can be counteracted by magnetic anisotropy. Previous efforts, based on defect and composition engineering, or the proximity effect, introduced magnetic responses only locally or extrinsically. Here we report intrinsic long-range ferromagnetic order in pristine Cr2Ge2Te6 atomic layers, as revealed by scanning magneto-optic Kerr microscopy. In this magnetically soft, two-dimensional van der Waals ferromagnet, we achieve unprecedented control of the transition temperature (between ferromagnetic and paramagnetic states) using very small fields (smaller than 0.3 tesla). This result is in contrast to the insensitivity of the transition temperature to magnetic fields in the three-dimensional regime. We found that the small applied field leads to an effective anisotropy that is much greater than the near-zero magnetocrystalline anisotropy, opening up a large spin-wave excitation gap. We explain the observed phenomenon using renormalized spin-wave theory and conclude that the unusual field dependence of the transition temperature is a hallmark of soft, two-dimensional ferromagnetic van der Waals crystals. Cr2Ge2Te6 is a nearly ideal two-dimensional Heisenberg ferromagnet and so will be useful for studying fundamental spin behaviours, opening the door to exploring new applications such as ultra-compact spintronics.

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Author and article information

Contributors

Jiyu Fan: (View ORCID Profile)

Lei Zhang: (View ORCID Profile)

Journal

Journal ID (publisher-id): CRECF4

Title: CrystEngComm

Abbreviated Title: CrystEngComm

Publisher: Royal Society of Chemistry (RSC)

ISSN (Electronic): 1466-8033

Publication date Created: January 18 2022

Publication date (Electronic): 2022

Volume: 24

Issue: 3

Pages: 674-680

Affiliations

[1 ]Department of Applied Physics, College of Physics Science, Nanjing University of Aeronautics and Astronautics, Nanjing 210016, China

[2 ]Key Laboratory of Aerospace Information Materials and Physics (NUAA), MIIT, Nanjing 211106, China

[3 ]Jiangsu Key Laboratory of Micro and Nano Heat Fluid Flow Technology and Energy Application, School of Physical Science and Technology, Suzhou University of Science and Technology, Suzhou, 215009, China

[4 ]High Magnetic Field Laboratory, Chinese Academy of Sciences, Hefei 230031, China

[5 ]Department of Physics Science and Technology, Baotou Normal College, Baotou 014030, China

[6 ]College of Physics Science and Technology, Yangzhou University, Yangzhou 225002, China

Article

DOI: 10.1039/D1CE01200B

SO-VID: 89f2d669-c666-4d5b-80f9-190f68078d54

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