April 2024

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/.

In the last decades enormous advances have been made in characterizing the atomic and molecular structure of respiratory chain supercomplexes. *

However, it still remains a challenge to stitch this refined spatial atomistic description with functional information provided by biochemical studies of isolated protein material. Development of functional assays that detect respiratory chain complexes in their native membrane environment contribute to address the open questions related to the role played by their association and interactions. *

In the article “Electrochemical detection of quinone reduced by Complex I Complex II and Complex III in full mitochondrial membranes” Daniel G. Cava, Julia Alvarez-Malmagro, Paolo Natale, Sandra López-Calcerrada, Iván López-Montero, Cristina Ugalde, Jose Maria Abad, Marcos Pita, Antonio L. De Lacey and Marisela Vélez present a characterization assay in which a functionalized gold electrode is modified with mitochondrial membrane fragments that allows monitoring electrochemically the activity of different respiratory chain complexes immersed in the mitochondrial membrane. *

Daniel G. Cava et al. measure the intensity of the reducing current of the electron mediator CoQ1 at the electrode surface and its variation upon addition of the corresponding enzymatic substrates. The activities of Complex I, Complex II and Complex III were monitored by the way in which they reduce the current, reflecting the amount of quinone reduced by the complexes in the presence of their substrates. *

The authors detect that CoQ1H2 produced by Complex I remains partially trapped within the membrane and is more easily oxidized by Complex III or the electrode than the quinone reduced by Complex II. *

Atomic Force Microscopy (AFM) was used to image the topography of the membrane modified electrode. NanoWorld Pyrex-Nitride Silicon-Nitride AFM probes (PNP-DB, diving board shaped cantilevers, the short AFM cantilever with a typical force constant of 0.48 N/m and 67 kHz resonance frequency) were used. *

The surfaces analysed were the electrodes. The two surfaces imaged are the same previously polished electrodes used for electrochemical measurements. The microscope sample holder was adapted in-home to support the electrodes. Two surfaces were analysed: the polished gold functionalized with 4-aminothiophenol and the electrode after incubation with mitochondria subparticles prepared similarly to the electrodes used for the electrochemical measurements.*

Fig. 2 from Daniel G. Cava et al 2024 “Electrochemical detection of quinone reduced by Complex I Complex II and Complex III in full mitochondrial membranes”
QCM and AFM characterization of modified gold. Panel A shows the frequency (left, black) and dissipation (right red) changes detected on a gold covered quartz crystal previously modified with a 4-ATP after injection in the chamber of the mitochondrial fragments at the time point indicated by the thick arrow. Panel B show AFM images of the surface topography of a modified gold electrode before (left) and after (right)incubation with the mitochondrial membrane. The inset below shows the height profile of the lines indicated in the images.

*Daniel G. Cava, Julia Alvarez-Malmagro, Paolo Natale, Sandra López-Calcerrada, Iván López-Montero, Cristina Ugalde, Jose Maria Abad, Marcos Pita, Antonio L. De Lacey and Marisela Vélez
Electrochemical detection of quinone reduced by Complex I Complex II and Complex III in full mitochondrial membranes
Electrochimica Acta, Volume 484, 20 April 2024, 144042
DOI: https://doi.org/10.1016/j.electacta.2024.144042

The article “Electrochemical detection of quinone reduced by Complex I Complex II and Complex III in full mitochondrial membranes” by Daniel G. Cava, Julia Alvarez-Malmagro, Paolo Natale, Sandra López-Calcerrada, Iván López-Montero, Cristina Ugalde, Jose Maria Abad, Marcos Pita, Antonio L. De Lacey and Marisela Vélez 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/.