The family of two-dimensional (2D) van der Waals (vdW) materials provides a playground for tuning structural and magnetic interactions to create a wide variety of spin textures. *
Of particular interest is the ferromagnetic compound Fe5GeTe2 that Ajesh K. Gopi et al. show displays a range of complex spin textures as well as complex crystal structures. *
In the article “Thickness-Tunable Zoology of Magnetic Spin Textures Observed in Fe5GeTe2”, using a high-brilliance laboratory X-ray source, Ajesh K. Gopi, Abhay K. Srivastava, Ankit K. Sharma, Anirban Chakraborty, Souvik Das, Hakan Deniz, Arthur Ernst, Binoy K. Hazra, Holger L. Meyerheim and Stuart S.P. Parkin show that the majority (1 × 1) Fe5GeTe2 (FGT5) phase exhibits a structure that was previously considered as being centrosymmetric but rather lacks inversion symmetry. *
In addition, FGT5 exhibits a minority phase that exhibits a long-range ordered (√3 × √3)-R30° superstructure. This superstructure is highly interesting in that it is innately 2D without any lattice periodicity perpendicular to the vdW layers, and furthermore, the superstructure is a result of ordered Te vacancies in one of the topmost layers of the FGT5 sheets rather than being a result of vertical Fe ordering as earlier suggested. *
Ajesh K. Gopi et al. show, from direct real-space magnetic imaging, evidence for three distinct magnetic ground states in lamellae of FGT5 that are stabilized with increasing lamella thickness, namely, a multidomain state, a stripe phase, and an unusual fractal state.
In the stripe phase the authors also observe unconventional type-I and type-II bubbles where the spin texture in the central region of the bubbles is nonuniform, unlike conventional bubbles.
In addition, they find a bobber or a cocoon-like spin texture in thick (∼170 μm) FGT5 that emerges from the fractal state in the presence of a magnetic field.
Among all the 2D vdW magnets Ajesh K. Gopi et al. have thus demonstrated that FGT5 hosts perhaps the richest variety of magnetic phases that, thereby, make it a highly interesting platform for the subtle tuning of magnetic interactions.
Magnetic force microscopy (MFM) measurements were performed in a commercially available variable-temperature magnetic force microscope equipped with a vector superconducting magnet.
NANOSENSORSTM SSS-MFMR, a magnetic AFM probe with an AFM tip radius of curvature < 15 nm was used for all MFM measurements.
MFM images were recorded in constant height mode. First, the topography of the sample was acquired in tapping mode after correcting the tilt and misalignment of the sample. Then, the MFM tip was lifted by 30–50 nm from above the sample during a second scan to measure the magnetic signal in noncontact mode. The phase shift of the AFM cantilever, caused by the magnetic interactions, was detected by using the phase modulation method.*
Figure 4. from Ajesh K. Gopi et al. 2024:
(a–e) MFM images of a bulk crystal with thickness ∼170 μm recorded at 100 K in the presence of an external field. Numbers in the upper right corner of each image show the corresponding field strength. (f) Magnified images of two selected regions (2 μm × 2 μm) in (e) showing two distinct magnetic contrasts. (g) Schematic representation showing the sample hosting different magnetic textures that result in different magnetic contrasts in MFM measurements.
*Ajesh K. Gopi, Abhay K. Srivastava, Ankit K. Sharma, Anirban Chakraborty, Souvik Das, Hakan Deniz, Arthur Ernst, Binoy K. Hazra, Holger L. Meyerheim and Stuart S.P. Parkin
Thickness-Tunable Zoology of Magnetic Spin Textures Observed in Fe5GeTe2
ACS Nano 2024, 18, 7, 5335–5343
DOI: https://doi.org/10.1021/acsnano.3c09602
The article “Thickness-Tunable Zoology of Magnetic Spin Textures Observed in Fe5GeTe2” by Ajesh K. Gopi, Abhay K. Srivastava, Ankit K. Sharma, Anirban Chakraborty, Souvik Das, Hakan Deniz, Arthur Ernst, Binoy K. Hazra, 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 license, unless indicated otherwise in a credit line to the material. If material is not included in the article’s Creative Commons license 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 license, visit https://creativecommons.org/licenses/by/4.0/.