skip to main content
US FlagAn official website of the United States government
dot gov icon
Official websites use .gov
A .gov website belongs to an official government organization in the United States.
https lock icon
Secure .gov websites use HTTPS
A lock ( lock ) or https:// means you've safely connected to the .gov website. Share sensitive information only on official, secure websites.

Explore Research Products in the PAR
It may take a few hours for recently added research products to appear in PAR search results.


Title: Revealing room temperature ferromagnetism in exfoliated Fe 5 GeTe 2 flakes with quantum magnetic imaging
Abstract Van der Waals (vdW) material Fe 5 GeTe 2 , with its long-range ferromagnetic ordering near room temperature, has significant potential to become an enabling platform for implementing novel spintronic and quantum devices. To pave the way for applications, it is crucial to determine the magnetic properties when the thickness of Fe 5 GeTe 2 reaches the few-layers regime. However, this is highly challenging due to the need for a characterization technique that is local, highly sensitive, artifact-free, and operational with minimal fabrication. Prior studies have indicated that Curie temperature T C can reach up to close to room temperature for exfoliated Fe 5 GeTe 2 flakes, as measured via electrical transport; there is a need to validate these results with a measurement that reveals magnetism more directly. In this work, we investigate the magnetic properties of exfoliated thin flakes of vdW magnet Fe 5 GeTe 2 via quantum magnetic imaging technique based on nitrogen vacancy centers in diamond. Through imaging the stray fields, we confirm room-temperature magnetic order in Fe 5 GeTe 2 thin flakes with thickness down to 7 units cell. The stray field patterns and their response to magnetizing fields with different polarities is consistent with previously reported perpendicular easy-axis anisotropy. Furthermore, we perform imaging at different temperatures and determine the Curie temperature of the flakes at ≈300 K. These results provide the basis for realizing a room-temperature monolayer ferromagnet with Fe 5 GeTe 2 . This work also demonstrates that the imaging technique enables rapid screening of multiple flakes simultaneously as well as time-resolved imaging for monitoring time-dependent magnetic behaviors, thereby paving the way towards high throughput characterization of potential two-dimensional (2D) magnets near room temperature and providing critical insights into the evolution of domain behaviors in 2D magnets due to degradation.  more » « less
Award ID(s):
1904076
PAR ID:
10351205
Author(s) / Creator(s):
; ; ; ; ; ; ; ; ; ; ; ; ;
Date Published:
Journal Name:
2D Materials
Volume:
9
Issue:
2
ISSN:
2053-1583
Page Range / eLocation ID:
025017
Format(s):
Medium: X
Sponsoring Org:
National Science Foundation
More Like this
  1. ; ; ; ; ; ; ; ; ; ; et al (, Advanced Functional Materials)
    Abstract Two‐dimentional magnets are of significant interest both as a platform for exploring novel fundamental physics and for their potential in spintronic and optoelectronic devices. Recent bulk magnetometry studies have indicated a weak ferromagnetic response in tungsten disulfide (WS2), and theoretical predictions suggest edge‐localized magnetization in flakes with partial hydrogenation. Here, room‐temperature wide‐field quantum diamond magnetometry to image pristine and Fe‐implanted WS2flakes of varying thicknesses (45–160 nm), exfoliated from bulk crystals and transferred to NV‐doped diamond substrates, is used. Direct evidence of edge‐localized stray magnetic fields, which scale linearly with applied external magnetic field (4.4–220 mT), reaching up to ±4.7 µT, is observed. The edge signal shows a limited dependence on the flake thickness, consistent with dipolar field decay and sensing geometry. Magnetic simulations using five alternative models favor the presence of edge magnetization aligned along an axis slightly tilted from the normal to the WS2flake's plane, consistent with spin canting in antiferromagnetically coupled edge states. Thses findings establish WS2as a promising platform for edge‐controlled 2D spintronics. 
    more » « less
  2. ; ; ; ; ; ; ; ; ; ; et al (, npj 2D Materials and Applications)
    Abstract Among several well-known transition metal-based compounds, cleavable van der Waals (vdW) Fe3-xGeTe2(FGT) magnet is a strong candidate for use in two-dimensional (2D) magnetic devices due to its strong perpendicular magnetic anisotropy, sizeable Curie temperature (TC~154 K), and versatile magnetic character that is retained in the low-dimensional limit. While the TCremains far too low for practical applications, there has been a successful push toward improving it via external driving forces such as pressure, irradiation, and doping. Here we present experimental evidence of a room temperature (RT) ferromagnetic phase induced by the electrochemical intercalation of common tetrabutylammonium cations (TBA+) into quasi-2D FGT. We obtained Curie temperatures as high as 350 K with chemical and physical stability of the intercalated compound. The temperature-dependent Raman measurements, in combination with vdW-corrected ab initio calculations, suggest that charge transfer (electron doping) upon intercalation could lead to the observation of RT ferromagnetism. This work demonstrates that molecular intercalation is a viable route in realizing high-temperature vdW magnets in an inexpensive and reliable manner, and has the potential to be extended to bilayer and few-layer vdW magnets. 
    more » « less
  3. ; ; ; ; ; ; ; ; (, Advanced Science)
    Abstract The van der Waals magnets CrX3(X = I, Br, and Cl) exhibit highly tunable magnetic properties and are promising candidates for developing novel two‐dimensional (2D) spintronic devices such as magnetic tunnel junctions and spin tunneling transistors. Previous studies of the antiferromagnetic CrCl3have mainly focused on mechanically exfoliated samples. Controlled synthesis of high quality atomically thin flakes is critical for their technological implementation but has not been achieved to date. This work reports the growth of large CrCl3flakes down to monolayer thickness via the physical vapor transport technique. Both isolated flakes with well‐defined facets and long stripe samples with the trilayer portion exceeding 60 µm have been obtained. High‐resolution transmission electron microscopy studies show that the CrCl3flakes are single crystalline in the monoclinic structure, consistent with the Raman results. The room temperature stability of the CrCl3flakes decreases with decreasing thickness. The tunneling magnetoresistance of graphite/CrCl3/graphite tunnel junctions confirms that few‐layer CrCl3possesses in‐plane magnetic anisotropy and Néel temperature of 17 K. This study paves the path for developing CrCl3‐based scalable 2D spintronic applications. 
    more » « less
  4. ; ; ; ; ; ; ; ; (, Advanced Functional Materials)
    Abstract Van der Waals (vdW) materials are an indispensable part of functional device technology due to their versatile physical properties and ease of exfoliating to the low‐dimensional limit. Among all the compounds investigated so far, the search for magnetic vdW materials has intensified in recent years, fueled by the realization of magnetism in 2D. However, metallic magnetic vdW systems are still uncommon. In addition, they rarely host high‐mobility charge carriers, which is an essential requirement for high‐speed electronic applications. Another shortcoming of 2D magnets is that they are highly air sensitive. Using chemical reasoning, TaCo2Te2is introduced as an air‐stable, high‐mobility, magnetic vdW material. It has a layered structure, which consists of Peierls distorted Co chains and a large vdW gap between the layers. It is found that the bulk crystals can be easily exfoliated and the obtained thin flakes are robust to ambient conditions after 4 months of monitoring using an optical microscope. Signatures of canted antiferromagntic behavior are also observed at low‐temperature. TaCo2Te2shows a metallic character and a large, nonsaturating, anisotropic magnetoresistance. Furthermore, the Hall data and quantum oscillation measurements reveal the presence of both electron‐ and hole‐type carriers and their high mobility. 
    more » « less
  5. ; ; ; ; ; ; ; ; ; ; et al (, Nature Communications)
    Abstract While the discovery of two-dimensional (2D) magnets opens the door for fundamental physics and next-generation spintronics, it is technically challenging to achieve the room-temperature ferromagnetic (FM) order in a way compatible with potential device applications. Here, we report the growth and properties of single- and few-layer CrTe 2 , a van der Waals (vdW) material, on bilayer graphene by molecular beam epitaxy (MBE). Intrinsic ferromagnetism with a Curie temperature ( T C ) up to 300 K, an atomic magnetic moment of ~0.21  $${\mu }_{{\rm{B}}}$$ μ B /Cr and perpendicular magnetic anisotropy (PMA) constant ( K u ) of 4.89 × 10 5  erg/cm 3 at room temperature in these few-monolayer films have been unambiguously evidenced by superconducting quantum interference device and X-ray magnetic circular dichroism. This intrinsic ferromagnetism has also been identified by the splitting of majority and minority band dispersions with ~0.2 eV at Г point using angle-resolved photoemission spectroscopy. The FM order is preserved with the film thickness down to a monolayer ( T C  ~ 200 K), benefiting from the strong PMA and weak interlayer coupling. The successful MBE growth of 2D FM CrTe 2 films with room-temperature ferromagnetism opens a new avenue for developing large-scale 2D magnet-based spintronics devices. 
    more » « less
  • Citation Formats
  • MLA
  • APA
  • Chicago
  • BibTeX
  • Save / Share this Record
  • Send to Email