Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii–Moriya Interaction

There is considerable interest in van der Waals (vdW) materials as potential hosts for chiral skyrmionic spin textures. Of particular interest is the ferromagnetic, metallic compound Fe3GeTe2 (FGT), which has a comparatively high Curie temperature (150–220 K). Several recent studies have reported the observation of chiral Néel skyrmions in this compound, which is inconsistent with its presumed centrosymmetric structure.*

In the article “Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii–Moriya Interaction” Anirban Chakraborty, Abhay K. Srivastava, Ankit K. Sharma, Ajesh K. Gopi, Katayoon Mohseni, Arthur Ernst, Hakan Deniz, Binoy Krishna Hazra, Souvik Das, Paolo Sessi, Ilya Kostanovskiy, Tianping Ma, Holger L. Meyerheim and Stuart S. P. Parkin report  the observation of Néel type skyrmions in single crystals of FGT via Lorentz transmission electron microscopy (LTEM).*

Since LTEM requires transmission of electrons through the sample thickness, the authors investigated the thicker lamella L2 using only magnetic force microscopy (MFM). *
For MFM measurements, the lamella was transferred on a prepatterned silicon substrate to be easily accessible by MFM tip. The measurements were performed in a vacuum and NANOSENSORS™ SuperSharpSilicon™ AFM probes for magnetic force microscopy (SSS-MFMR) were used for all measurements. *

In the article it is shown from detailed X-ray diffraction structure analysis that FGT lacks an inversion symmetry as a result of an asymmetric distribution of Fe vacancies. This vacancy-induced breaking of the inversion symmetry of this compound is a surprising and novel observation and is a prerequisite for a Dzyaloshinskii–Moriya vector exchange interaction which accounts for the chiral Néel skyrmion phase. This phenomenon is likely to be common to many 2D vdW materials and suggests a path to the preparation of many such acentric compounds. *

Furthermore, it is found that the skyrmion size in FGT is strongly dependent on its thickness: the skyrmion size increases from ≈100 to ≈750 nm as the thickness of the lamella is increased from ≈90 nm to ≈2 µm. This extreme size tunability is a feature common to many low symmetry ferro- and ferri-magnetic compounds. *

Figure 4 from “Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii–Moriya Interaction” by Anirban Chakraborty et al. Thickness dependence of skyrmion size in lamella L2 as imaged by MFM. a) SEM image of the wedge-shaped lamella. The thickness of the lamella varies from ≈100 nm to ≈2 µm. b) MFM image of skyrmions in the lamella at 100 K and 0.032 T. c–f) Evolution of skyrmions as the field is increased from 0.1 to 0.2 T and finally reaches the field polarized state at ≈0.3 T. The blue and red contrast in the MFM images represent up- and down-magnetized domains. All MFM images are at the same scale: a scale bar is shown in (b). g) Skyrmion diameter as a function of lamella thickness including both MFM and LTEM data. NANOSENSORS SSS-MFMR AFM probes for magnetic force microscopy were used for all MFM measurements.
Figure 4 from “Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii–Moriya Interaction” by Anirban Chakraborty et al.
Thickness dependence of skyrmion size in lamella L2 as imaged by MFM. a) SEM image of the wedge-shaped lamella. The thickness of the lamella varies from ≈100 nm to ≈2 µm. b) MFM image of skyrmions in the lamella at 100 K and 0.032 T. c–f) Evolution of skyrmions as the field is increased from 0.1 to 0.2 T and finally reaches the field polarized state at ≈0.3 T. The blue and red contrast in the MFM images represent up- and down-magnetized domains. All MFM images are at the same scale: a scale bar is shown in (b). g) Skyrmion diameter as a function of lamella thickness including both MFM and LTEM data.

*Anirban Chakraborty, Abhay K. Srivastava, Ankit K. Sharma, Ajesh K. Gopi, Katayoon Mohseni, Arthur Ernst, Hakan Deniz, Binoy Krishna Hazra, Souvik Das, Paolo Sessi, Ilya Kostanovskiy, Tianping Ma, Holger L. Meyerheim and Stuart S. P. Parkin
Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii–Moriya Interaction
Advanced Materials, Volume 34, Issue 11, March 17, 2022, 2108637
DOI: https://doi.org/10.1002/adma.202108637

Open Access: The article “Magnetic Skyrmions in a Thickness Tunable 2D Ferromagnet from a Defect Driven Dzyaloshinskii–Moriya Interaction” by Anirban Chakraborty, Abhay K. Srivastava, Ankit K. Sharma, Ajesh K. Gopi, Katayoon Mohseni, Arthur Ernst, Hakan Deniz, Binoy Krishna Hazra, Souvik Das, Paolo Sessi, Ilya Kostanovskiy, Tianping Ma, Holger L. Meyerheim and Stuart S. P. Parkin is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit https://creativecommons.org/licenses/by/4.0/.

Monitoring SARS-CoV-2 Surrogate TGEV Individual Virions Structure Survival under Harsh Physicochemical Environments

Successful airborne transmission of coronaviruses through fluid microdroplets requires a virion structure that must withstand harsh natural conditions. *

Because of the strict biosafety requirements for the study of human respiratory viruses, it is important to develop surrogate models to facilitate their investigation. *

In the article “Monitoring SARS-CoV-2 Surrogate TGEV Individual Virions Structure Survival under Harsh Physicochemical Environments” Miguel Cantero, Diego Carlero, Francisco Javier Chichón, Jaime Martín-Benito and Pedro José De Pablo explore the mechanical properties and nanostructure of transmissible gastroenteritis virus (TGEV) virions in liquid milieu and their response to different chemical agents commonly used as biocides in their quest for a SARS-CoV2 surrogate for dynamic nanoscale structure studies that can alleviate the use of BSL3 labs that are highly demanded for biomedical and biotechnological research. *

In past few years, atomic force microscopy (AFM) has been used to thoroughly characterize the physical properties, structure and stability of many viruses. *

It is possible to scan individual viruses, obtaining their topography and a variety of physical properties such as mechanics or electrostatics in controlled liquid milieu. Atomic Force Microscopy has provided biophysical information on all kinds of viruses, including bacteriophages and eukaryotic viruses. *

For the research described in their article the authors used AFM to explore in real time the stability of individual TGEV particles as a surrogate model for SARS-CoV-2 in order to elucidate its structural stability under a range of physicochemical assaults, including mechanical stress, desiccation-rehydration cycles and treatment with chemical agents commonly used as biocides, such as detergents and ethanol. *

They also aimed to show that some structural research can be performed with non-hazardous CoV strains. *

All the described AFM experiments were carried out with NANOSENSORS™ uniqprobe qp-BioAC AFM probes. *

The data collected by Miguel Cantero  et al. for the article provide two-fold results on virus stability:

First, while particles with larger size and lower packing fraction kept their morphology intact after successive mechanical aggressions, smaller viruses with higher packing fraction showed conspicuous evidence of structural damage and content release.

Second, monitoring the structure of single TGEV particles in the presence of detergent and alcohol in real time revealed the stages of gradual degradation of the virus structure in situ. *

These data suggest that detergent is three orders of magnitude more efficient than alcohol in destabilizing TGEV virus particles, paving the way for optimizing hygienic protocols for viruses with similar structure, such as SARS-CoV-2. *

Figure 3 from “Monitoring SARS-CoV-2 Surrogate TGEV Individual Virions Structure Survival under Harsh Physicochemical Environments” by Miguel Cantero et al.: Treatment of TGEV with IGEPAL 0.2% (A). Topographical images before (left) and after (right) IGEPAL treatment (B). Profiles traced over the particles before (black) and after (blue) the treatment. The time interval between images was ~30 s (C). Height distribution of TGEV particles before (black) and after (blue) treatment (n = 103). Counts taken from the distribution curve were normalized for comparison. The peak shifts from the value of the intact particle height to the height of the cores. NANOSENSORS uniqprobe qp-BioAC AFM probes were used for the atomic force microscopy measurements.
Figure 3 from “Monitoring SARS-CoV-2 Surrogate TGEV Individual Virions Structure Survival under Harsh Physicochemical Environments” by Miguel Cantero et al.:
Treatment of TGEV with IGEPAL 0.2% (A). Topographical images before (left) and after (right) IGEPAL treatment (B). Profiles traced over the particles before (black) and after (blue) the treatment. The time interval between images was ~30 s (C). Height distribution of TGEV particles before (black) and after (blue) treatment (n = 103). Counts taken from the distribution curve were normalized for comparison. The peak shifts from the value of the intact particle height to the height of the cores.

*Miguel Cantero, Diego Carlero, Francisco Javier Chichón, Jaime Martín-Benito and Pedro José De Pablo
Monitoring SARS-CoV-2 Surrogate TGEV Individual Virions Structure Survival under Harsh Physicochemical Environments
Cells 2022, 11(11), 1759
DOI: https://doi.org/10.3390/cells11111759

Open Access: The article “Monitoring SARS-CoV-2 Surrogate TGEV Individual Virions Structure Survival under Harsh Physicochemical Environments” by Miguel Cantero, Diego Carlero, Francisco Javier Chichón, Jaime Martín-Benito and Pedro José De Pablo is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The images or other third party material in this article are included in the article’s Creative Commons licence, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons licence and your intended use is not permitted by statutory regulation or exceeds the permitted use, you will need to obtain permission directly from the copyright holder. To view a copy of this licence, visit http://creativecommons.org/licenses/by/4.0/.