Quantitative Imaging of the Magnetic Configuration of Modulated Nanostructures by Electron Holography

• Published in: Small (Weinheim an der Bergstrasse, Germany) Germany), 2014-12, Vol.10 (24), p.5161-5169
• Main Authors: Körner, Michael, Röder, Falk, Lenz, Kilian, Fritzsche, Monika, Lindner, Jürgen, Lichte, Hannes, Fassbender, Jürgen
• Format: Article
• Language: English
• Subjects: electron holography; ferromagnetism; Ferrous alloys; Holography; Magnetization; Morphology; Nanostructure; nanostructures; Nanotechnology; Nickel base alloys; Permalloy; Ripples; Simulation; stray fields; Thin films
• ISSN: 1613-6810; 1613-6829
• DOI: 10.1002/smll.201400377

By means of off‐axis electron holography the local distribution of the magnetic induction within and around a poly‐crystalline Permalloy (Ni81Fe19) thin film is studied. In addition the stray field above the sample is measured by magnetic force microscopy on a larger area. The film is deposited on a periodically nanostructured (rippled) Si substrate, which was formed by Xe+ ion beam erosion. This introduces the periodical ripple shape to the Permalloy film. The created ripple morphology is expected to modify the magnetization distribution within the Permalloy and to induce dipolar stray fields. These stray fields play an important role in spinwave dynamics of periodic nanostructures like magnonic crystals. Micromagnetic simulations estimate those stray fields in the order of only 10 mT. Consequently, their experimental determination at nanometer spatial resolution is highly demanding and requires advanced acquisition and reconstruction techniques such as electron holography. The reconstructed magnetic phase images show the magnetized thin film, in which the magnetization direction follows mainly the given morphology. Furthermore, a closer look to the Permalloy/carbon interface reveals stray fields at the detection limit of the method in the order of 10 mT, which is in qualitative agreement with the micromagnetic simulations. The magnetic configuration and stray fields of a rippled (nanomodulated), ferromagnetic Permalloy thin film is quantitatively analyzed using off‐axis transmission electron holography. Stray fields of 10–20 mT are observable, emerging from the short ripple flank. The results are corroborated by micro‐magnetic simulations.