磁性力调制显微镜

Spin Seebeck effects (SSE) arise from spin current (magnon) generation from within ferri-, ferro-, or anti-ferromagnetic materials driven by an applied temperature gradient. *

Longitudinal spin Seebeck effect (LSSE) investigations, where the spin current and temperature gradient evolve along a common z axis, while the magnetic field is applied in the y axis and the voltage contacts are spaced along the x axis, have become the most popular spin Seebeck device architecture. *

In article “Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect”, Yaoyang Hu, Michael P. Weir, H. Jessica Pereira, Oliver J. Amin, Jem Pitcairn, Matthew J. Cliffe, Andrew W. Rushforth, Gunta Kunakova, Kiryl Niherysh, Vladimir Korolkov, James Kertfoot, Oleg Makarovsky and Simon Woodward present a method to enhance the longitudinal spin Seebeck effect at platinum/yttrium iron garnet (Pt/YIG) interfaces. *

The introduction of a partial interlayer of bismuth selenide (Bi2Se3, 2.5% surface coverage) interfaces significantly increases (by ∼380%–690%) the spin Seebeck coefficient over equivalent Pt/YIG control devices. *

Optimal devices are prepared by transferring Bi2Se3 nanoribbons, prepared under anaerobic conditions, onto the YIG (111) chips followed by rapid over-coating with Pt. The deposited Pt/Bi2Se3 nanoribbon/YIG assembly is characterized by scanning electron microscope. The expected elemental compositions of Bi2Se3 and YIG are confirmed by energy dispersive x-ray analysis. *

A spin Seebeck coefficient of 0.34–0.62 μV/K for Pt/Bi2Se3/YIG is attained for the authors’ devices, compared to just 0.09 μV/K for Pt/YIG controls at a 12 K thermal gradient and a magnetic field swept from −50 to +50 mT. *

Superconducting quantum interference device magnetometer studies indicate that the magnetic moment of Pt/Bi2Se3/YIG treated chips is increased by ∼4% vs control Pt/YIG chips (i.e., a significant increase vs the ±0.06% chip mass reproducibility). *

Increased surface magnetization is also detected in magnetic force microscope studies of Pt/Bi2Se3/YIG, suggesting that the enhancement of spin injection is associated with the presence of Bi2Se3 nanoribbons. *

To understand the surface magnetization effects in sample BSYIG1-a further, magnetic force microscope (MFM) measurements were undertaken using a commercial atomic force microscope and magnetic NanoWorld Pointprobe® MFMR AFM probes. *

MFM differs from traditional atomic force microscopy in that the AFM probe, in addition to providing a surface height profile, is also able to detect the magnetic field gradient above the sample. *

MFM surface profiling of BSYIG1-a revealed that a typical ribbon is comprised of multilayers of Bi2Se3, providing thicker sections ca. 250 nm thick [e.g., the profile along vector 1 in Figs. 3(a) and 3(b) cited below] and additional thinner sections ca. 100 nm thick [e.g., the profile along vector 2 in Figs. 3(a) and 3(b)]. Re-running ribbon profiles 1 and 2 with the magnetic probe at a height of 100 nm above the topological surface provided data on the magnetic field gradient variation along the same line profiles. The MFM amplitude [Figs. 3(c) and 3(d) cited below] increases over the Bi2Se3 flake, and furthermore, the magnetic enhancement correlates with the thickness of the Bi2Se3, being larger for the thicker part of the sample. *

This amplitude enhancement suggests that the observed effect is magnetic rather than due to long-range electrostatics, supporting the inference that the surface magnetization is improved by the presence of Bi2Se3 flakes at the interlayer of a Pt/YIG device. However, it was not possible to extract quantitative information about surface magnetization from this study, but Yaoyang Hu et al. are hopeful that future experimental and theoretical work can provide further explanation. *

Figure 3 from Yaoyang Hu et al. “Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect”:
Scanning probe microscopy images of BSYIG1-a: (a) Atomic force microscopy image of a representative Bi2Se3 nanoribbon on a YIG/GGG substrate. (b) Bi2Se3 ribbon profile scans along vectors 1 (pink) and 2 (blue) showing the two differential height responses. (c) Magnetic force microscopy image of the same Bi2Se3 nanoribbon. The measurement was performed at 100 nm above the topological heights determined in the AFM study. (d) MFM profile scans along vectors 1 (pink) and 2 (blue) showing the magnetic response.

*Yaoyang Hu, Michael P. Weir, H. Jessica Pereira, Oliver J. Amin, Jem Pitcairn, Matthew J. Cliffe, Andrew W. Rushforth, Gunta Kunakova, Kiryl Niherysh, Vladimir Korolkov, James Kertfoot, Oleg Makarovsky and Simon Woodward
Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect
Applied Physics Letters 123, 223902 (2023)
DOI: https://doi.org/10.1063/5.0157778

The article “Bi2Se3 interlayer treatments affecting the Y3Fe5O12 (YIG) platinum spin Seebeck effect” by Yaoyang Hu, Michael P. Weir, H. Jessica Pereira, Oliver J. Amin, Jem Pitcairn, Matthew J. Cliffe, Andrew W. Rushforth, Gunta Kunakova, Kiryl Niherysh, Vladimir Korolkov, James Kertfoot, Oleg Makarovsky and Simon Woodward 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/.

Magnetic nano-objects, namely antiskyrmions and Bloch skyrmions, have been found to coexist in single-crystalline lamellae formed from bulk crystals of inverse tetragonal Heusler compounds with D2d symmetry. *

Skyrmions can be observed in real-space by various direct imaging techniques. *

In the article “Nanoscale Noncollinear Spin Textures in Thin Films of a D2d Heusler Compound” Ankit K. Sharma, Jagannath Jena, Kumari Gaurav Rana, Anastasios Markou, Holger L. Meyerheim, Katayoon Mohseni, Abhay K. Srivastava, Ilya Kostanoskiy, Claudia Felser and Stuart S. P. Parkin describe the use of magnetic force microscopy (MFM) imaging to investigate magnetic textures in epitaxial thin films of [001]-oriented Mn2RhSn formed by magnetron sputtering.*

They find evidence for magnetic nano-objects which exhibit a wide range of sizes with stability with respect to magnetic field and temperature that is similar to single-crystalline lamellae. *

However, the nano-objects do not form well-defined arrays, nor is any evidence found for helical spin textures. This is speculated to likely be a consequence of the poorer homogeneity of chemical ordering in the thin films. *

Evidence is found for elliptically distorted nano-objects along perpendicular crystallographic directions within the epitaxial films, which is consistent with elliptical Bloch skyrmions observed in single-crystalline lamellae. Thus, these measurements provide strong evidence for the formation of noncollinear spin textures in thin films of Mn2RhSn. *

Using these films, it is shown that individual nano-objects can be deleted using a local magnetic field from a magnetic AFM tip and collections of nano-objects can be similarly written. *

For writing and deleting the nano-objects, magnetic AFM probes from NanoWorld of the Pointprobe® MFMR type were used. *

These observations described in the article suggest a path toward the use of these nano-objects in thin films with D2d symmetry as magnetic memory elements paving the way to the realization of skyrmionic devices based on Heusler thin films. *

Figure 5 from Ankit K. Sharma et al. Nanoscale Noncollinear Spin Textures in Thin Films of a D2d Heusler Compound : Controlled creation and annihilation of nano-objects in a 35 nm-thick Mn2RhSn thin film. a) Schematic illustration of magnetization orientations of MFM tip and sample for writing. The distance between tip and the sample is the scan height z. b–e) MFM images in zero field and z = 80, 40, 30, and 20 nm, respectively at 200 K. f) Contact-mode image in zero field and 200 K. The blue and red colors represent up and down magnetization, respectively. Images in (b)–(f) are at the same scale: a scale bar is given in (f). g–i) MFM images taken at z = 70, 50, and 30 nm at 100 K under Hz = 180 mT. Images in (g)–(i) are at the same scale: a scale bar is given in (i). For writing and deleting the nano-objects, magnetic AFM probes from NanoWorld of the Pointprobe® MFMR type were used. — Figure 5 from Ankit K. Sharma et al. Nanoscale Noncollinear Spin Textures in Thin Films of a D2d Heusler Compound :
Controlled creation and annihilation of nano-objects in a 35 nm-thick Mn2RhSn thin film. a) Schematic illustration of magnetization orientations of MFM tip and sample for writing. The distance between tip and the sample is the scan height z. b–e) MFM images in zero field and z = 80, 40, 30, and 20 nm, respectively at 200 K. f) Contact-mode image in zero field and 200 K. The blue and red colors represent up and down magnetization, respectively. Images in (b)–(f) are at the same scale: a scale bar is given in (f). g–i) MFM images taken at z = 70, 50, and 30 nm at 100 K under Hz = 180 mT. Images in (g)–(i) are at the same scale: a scale bar is given in (i).

*Ankit K. Sharma, Jagannath Jena, Kumari Gaurav Rana, Anastasios Markou, Holger L. Meyerheim, Katayoon Mohseni, Abhay K. Srivastava, Ilya Kostanoskiy, Claudia Felser, Stuart S. P. Parkin
Nanoscale Noncollinear Spin Textures in Thin Films of a D2d Heusler Compound
Advanced Materials, Volume 33, Issue 32, August 12, 2021, 2101323
DOI: https://doi.org/10.1002/adma.202101323

Open Access The article “Nanoscale Noncollinear Spin Textures in Thin Films of a D2d Heusler Compound” Ankit K. Sharma, Jagannath Jena, Kumari Gaurav Rana, Anastasios Markou, Holger L. Meyerheim, Katayoon Mohseni, Abhay K. Srivastava, Ilya Kostanoskiy, Claudia Felser 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 http://creativecommons.org/licenses/by/4.0/.