Tag Archives: magnetic properties and materials

Observing single magnetite nanoparticles with a diameter of 10nm by using NANOSENSORS SSS-MFMR AFM probes

In their publication “Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single supermagnetic nanoparticle resolution” Alexander Krivcov, Tanja Junkers and Hildegard Möbius describe methods to suppress capacitive coupling effects in MFM hiding the magnetic signal of magnetic nanoparticles.

During MFM measurements performed in an interleave mode moving the tip at a certain distance to the sample surface the tip is exposed not only to magnetic forces but to electrostatic forces between tip and substrates. In case of analyzing nanoparticles laying on a flat substrate, the electrostatic forces changes noticeably with increasing tip to substrate distance whenever the tip is retracted over a nanoparticle. This capacitive signal may overwhelm the magnetic signal that should be detected instead.

The authors propose several approaches to reduce these capacitive signals. The change in electrostatic forces could be minimized by avoiding retraction of tip over the nanoparticle. Therefore, it is proposed to use interleave linear mode following a linear approximation of the sample surface instead of the interleave lift mode following the sample surface as measured. By that, changes in distance between sample substrate and tip at the nanoparticles are avoided. Moreover, they propose using a substrate with a work function comparable to that of the tip in order to reduce electrostatic forces, in general. By applying an appropriate tip bias remaining electrostatic forces could compensated and further suppressed. Finally, the authors suggest using a tip that is as sharp as possible for decreasing the area of the capacitor and NANOSENSORS SSS-MFMR probes are the best choice for this.

The impact of the above mentioned optimizations have been validated experimentally by the authors. Finally, it turned out that if using super sharp magnetic tips further methods suppressing capacitive effects were not necessary. The authors were able to detect superparamagnetic nanoparticles at the single particle level on copper substrate with a NANOSENSORS SSS-MFMR probe without using additional parameters as e. g. tip bias or external magnetic field.Figure 12 from: A. Krivcov et. al, Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single supermagnetic nanoparticle resolution: Figure 12. (a) topography of copper substrate with single magnetite nanoparticle; (b) phase image in 11 nm lift height with an attraction at the place of the nanoparticle; (c) Cross section of a single magnetite nanoparticle (dotted line in (a)) with 10 nm diameter taken on copper substrate with NANOSENSORS SSS-MFMR AFM probe

Figure 12  from: A. Krivcov et. al, Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single supermagnetic nanoparticle resolution: Figure 12. (a) topography of copper substrate with single magnetite nanoparticle; (b) phase image in 11 nm lift height with an attraction at the place of the nanoparticle; (c) Cross section of a single magnetite nanoparticle (dotted line in (a)) with 10 nm diameter taken on copper substrate with SSS-MFMR tip

A. Krivcov, T. Junkers, and H. Möbius
Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single superparamagnetic nanoparticle resolution
J. Phys. Commun., vol. 2, no. 7, p. 075019, 2018
DOI: https://doi.org/10.1088/2399-6528/aad3a4

The article “Understanding electrostatic and magnetic forces in magnetic force microscopy: towards single superparamagnetic nanoparticle resolution” by A. Krivcov, T. Junkers, and H. Möbius is licensed under the Creative Commons Attribution 3.0 License. To view a copy of this license, visit http://creativecommons.org/licenses/by/3.0.

Resonant torsion magnetometry in anisotropic quantum materials

Who said that AFM probes can only be used for Atomic Force Microscopy?

In the article “Resonant torsion magnetometry in anisotropic quantum materials” which just appeared in Nature Communications, K. A. Modic, Maja D. Bachmann, B. J. Ramshaw, F. Arnold, K. R. Shirer, Amelia Estry, J. B. Betts, Nirmal J. Ghimire, E. D. Bauer, Marcus Schmidt, Michael Baenitz, E. Svanidze, Ross D. McDonald, Arkady Shekhter and Philip J. W. Moll use the NANOSENSORS™ Akiyama-probe for resonant torsion magnetometry.

Figure 1 from "Resonant torsion magnetometry in anisotropic quantum materials": Schematic overview of resonant torsion magnetometry. a First and second derivatives of the free energy with respect to the magnetic field B and the field orientation θ. b The quartz tuning fork of the Akiyama A-probe (http://www.akiyamaprobe.com) is electrically excited at the lowest-resonance mode of the silicon cantilever, producing a large out-of-plane motion at the tip of the cantilever. c Schematic representing the principle of measuring the magnetotropic coefficient k. In a magnetic field, the magnetic torque brings the lever to a new equilibrium position. The magnetic energy of the samples changes the effective stiffness of the lever, leading to a shift in the resonant frequency. d The silicon cantilever glued to each leg of the quartz tuning fork with a single crystal of RuCl3 mounted at the tip with Bayer silicone grease
Figure 1 from “Resonant torsion magnetometry in anisotropic quantum materials”: Schematic overview of resonant torsion magnetometry a First and second derivatives of the free energy with respect to the magnetic field B and the field orientation θ. b The quartz tuning fork of the Akiyama A-probe (http://www.akiyamaprobe.com) is electrically excited at the lowest-resonance mode of the silicon cantilever, producing a large out-of-plane motion at the tip of the cantilever. c Schematic representing the principle of measuring the magnetotropic coefficient k. In a magnetic field, the magnetic torque brings the lever to a new equilibrium position. The magnetic energy of the samples changes the effective stiffness of the lever, leading to a shift in the resonant frequency. d The silicon cantilever glued to each leg of the quartz tuning fork with a single crystal of RuCl3 mounted at the tip with Bayer silicone grease

There are three advantages why it makes sense to divert the NANOSENSORS™ Akiyama-probe from it’s orginal intended use and use it for resonant torque magnetometry instead:

1. the relatively large spring constant of the silicon cantilever allows the authors to extend ultrasensitive and dynamic cantilever magnetometry to macroscopic sample sizes

  1. “the placement of the sample on the silicon cantilever (rather than one leg of a quartz tuning fork) eliminates complications that arise from the center of mass motion of the tuning fork coupling to the resonance mode

3. the electrical read-out of the A-probe eliminates the need for optical detection of the resonant frequency, thus making setup relatively straightforward and more robust compared to previous approaches.”*

*K. A. Modic, Maja D. Bachmann, B. J. Ramshaw, F. Arnold, K. R. Shirer, Amelia Estry, J. B. Betts, Nirmal J. Ghimire, E. D. Bauer, Marcus Schmidt, Michael Baenitz, E. Svanidze, Ross D. McDonald, Arkady Shekhter; Philip J. W. Moll
Resonant torsion magnetometry in anisotropic quantum materials
Nature Communications, volume 9, Article number: 3975 (2018)
DOI: https://doi.org/10.1038/s41467-018-06412-w

For the full article please follow this external link: https://rdcu.be/7Z0A

Open Access The article “Resonant torsion magnetometry in anisotropic quantum materials” by K.A. Modic et. al 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/.