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

Abstract

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.

Direct Depth- and Lateral- Imaging of Nanoscale Magnets Generated by Ion Impact

“…We apply Off-Axis Electron Holography 25 26 27 , in TEM to measure the formation of the magnetic fields within and around the magnetic nanostructures. This technique was successfully applied to measure magnetic fields with nanometer spatial resolution in the past 28 29 30 . By means of the Möllenstedt biprism 31 , an electron wave passing through the object is coherently superimposed with a reference wave passing through field-free space forming an interference fringe pattern -the hologram- at the detector plane ( Fig.…”

Role of internal demagnetizing field for the dynamics of a surface-modulated magnonic crystal

“…Off-axis electron holography 42 was employed as a unique technique to quantitatively map the projected magnetic induction 43 at a spatial resolution of about 2 nm and a magnetic phase signal resolution of about 2π/100 rad. The imaging of the lamella was carried out in remanence using a HITACHI HF3300 (I2TEM) transmission electron microscope with a 300 kV cold field emission gun and two goniometer stages (a field-free Lorentz stage and a standard high resolution stage).…”

Mapping the magnetic and crystal structure in cobalt nanowires

“…[22][23][24][25][26][27] In this matter, TEM offers the possibility to combine specialized techniques to investigate structure-property relationships at scales ranging from a few microns to a few nanometers. [28][29][30][31][32][33] For instance, off-axis electron holography affords the study of the magnetization distribution inside nanostructures in a detailed manner, while the coupling of nano-probe scanning and precession electron diffraction is a powerful technique developed to automatically obtain crystallographic orientation/phase maps of nanosized polycrystalline structures. 34 Precession electron diffraction (PED) is a technique that collects electron diffraction patterns under a conical oscillation of the electron beam leading in a significant reduction of the dynamical effects due to the thickness of the sample.…”